Jennifer C. Peddle B.Sc.H. A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF

Jennifer C. Peddle B.Sc.H. A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF
Biodiversity and community ecology of the parasites of the three-spine
stickleback, Gasterosteus aculeatus, in the southern Gulf of St. Lawrence
by
Jennifer C. Peddle
B.Sc.H.
A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF
THE REQUIREMENTS FOR THE DEGREE OF
Masters of Science
In the Graduate Academic Unit of Biology
Supervisor:
Kelly Munkittrick, PhD Dept of Biology, UNBSJ
Examining Board:
(name, degree, department/field), Chair
(name, degree, department/field)
This thesis is accepted
_________________________
Dean of Graduate Studies
THE UNIVERSITY OF NEW BRUNSWICK
August, 2004
© Jennifer Peddle, 2004
ABSTRACT
The three-spine stickleback, Gasterosteus aculeatus, is one of the most
studied fishes found in the southern Gulf of St. Lawrence (sGSL), but little is
known about their parasites. This project was designed to create a biodiversity
inventory of the macro- ectoparasites and endoparasites of three-spine
sticklebacks, and to examine these parasites in terms of community ecology.
Ectoparasite numbers were much lower than expected, and consisted primarily
of Gyrodactylus sp.(prevalence 34.4%, 39 of 110 fish), Ergasilus sp. (17.2%, 19
of 110 fish), Thersitina gasterostei (0.08%, 9 of 110 fish) and cysts embedded in
the gill. The endoparasites, consisted primarily of 12 species of Digenea; only 3
have previously been recorded from three-spine stickleback. Brachyphallus
crenatus occurred in 82% of fish (74/90), Podocotyle angulata occurred in 38% of
fish (19/50), and digenean ‘F’ a member of the Family Lecithasteridae (potentially
Lecithaster gibbosus) occurred in only three estuaries with a maximum intensity
of two. The nine digenea remaining are new host records and potential new area
records for digenea found in three-spines. Other species were not widely
distributed. Distributions of endoparasites could not be correlated with
endoparasite numbers, and neither group correlated with environmental
parameters or geographic distributions. The number of digeneans did correlate
with human population size and the number of primary resource workers,
suggesting that eutrophication and potentially fish plants contributed to higher
levels of infection.
ii
ACKNOWLEDGMENTS
iii
TABLE OF CONTENTS
ABSTRACT ......................................................................................................... ii
ACKNOWLEDGMENTS ..................................................................................... iii
LIST OF TABLES .............................................................................................. vii
LIST OF FIGURES ........................................................................................... viii
CHAPTER 1
1
GENERAL INTRODUCTION .............................................................................. 1
1.1.
Parasites as bioindicators in ecological assessment .......................... 1
1.2 Background to the present study ................................................................ 2
1.3 Study Area .................................................................................................. 3
1.3.1 Previous studies in this area .................................................................... 4
1.4 Statement of Problem ................................................................................. 6
1.5 Objectives and organization of thesis.......................................................... 6
1.5.1 Objectives ................................................................................................ 6
1.5.2 Hypotheses .............................................................................................. 7
1.5.3 Organization of the Thesis ....................................................................... 7
Chapter 2............................................................................................................ 8
Overview of the geographic distribution and biology of the host and parasites . 8
2.1 Geographic distribution of the three-spine stickleback ................................ 8
2.2 Biology of the three-spine stickleback ......................................................... 9
2.3 Major parasites being considered in this study ......................................... 10
2.3.1 Ectoparasites ......................................................................................... 13
iv
2.3.2 Endoparasites ........................................................................................ 16
2.3.3 Relevant Literature................................................................................. 21
Chapter 3...........................................................................................................24
Materials and Methods ......................................................................................24
3.1 Study sites ................................................................................................ 24
3.2 Sample Collection ..................................................................................... 27
3.3 Dissections and preservation .................................................................... 28
3.4 Staining and Mounting .............................................................................. 30
3.5 Parasite identification ................................................................................ 34
3.6 Statistical analyses ................................................................................... 34
Chapter 4
36
Results ..............................................................................................................36
4.1 Biodiversity................................................................................................ 36
4.1.2
Ectoparasites ................................................................................ 36
4.1.2
Endoparasites ............................................................................... 44
4.2 Community Ecology .................................................................................. 70
4.2.1 Ectoparasites ......................................................................................... 70
4.2.2 Endoparasites ........................................................................................ 81
Chapter 5
90
Discussion .........................................................................................................90
5.1 Parasite fauna of the three-spine stickleback............................................ 91
5.1.1 Ectoparasites ......................................................................................... 91
5.1.2 Endoparasites ........................................................................................ 94
v
5.2 Community Ecology .................................................................................. 98
5.2.1 Ectoparasites ......................................................................................... 98
5.2.2 Endoparasites ........................................................................................ 99
5.2.3 Relationship to environmental factors ...................................... 102
Chapter 6
107
Conclusion.......................................................................................................107
6.1 Biodiversity.............................................................................................. 107
6.1.1 Overall .............................................................................................. 107
6.1.2 DIVERSITAS data set.............................................................. 108
6.2 Community Ecology ................................................................................ 109
6.3 Environmental Status .......................................................................... 110
REFERENCES ................................................................................................112
vi
LIST OF TABLES
Table 1 General life history characteristics of the different parasites discussed in
this paper (Roberts and Janovy 1996, Hoffman 1999) * (See Figure 2)
.........................................................................................................11
Table 2: Ectoparasite records found from the literature (Beverley-Burton 1984,
Kabata 1988, Rafi 1988, Bousfield & Kabata 1988). 1 denotes that
the parasite was found and 0 denotes no report. Abbreviations:
AT=Atlantic Ocean, NL=Newfoundland and Labrador, NS=Nova
Scotia, NB=New Brunswick, PEI=Prince Edward Island, QC=Quebec,
ON=Ontairo, MN=Manitoba, BC=British Columbia, NT=North West
Territories, YK=Yukon Territory, PC=Pacific Ocean, Mg=Monogenea,
B=Branchiura, Cp=Copepoda..........................................................22
Table 3: Parasites from the literature of Gasterosteus aculeatus in Canada. 1
denotes that the parasite was found, 0 denotes no record. Provincial
abbreviations as in Table 2, parasite abbreviations: D=Digenea,
T=Cestoidea, A=Acanthocephala. ...................................................23
Table 4: Estuaries sampled, date of collection, GPS coordinates of each estuary,
and average water temperature and salinity at the time of sampling.26
Table 5: Keys used for identification of parasites. ............................................34
Table 6: Taxonomic designations of ectoparasite types collected in the sGSL. 37
Table 7: Abundance of each parasite species in each estuary with the total
number of each parasite species collected from the sGSL, the total
number of parasites collected per estuary, the number of different
parasites found at each site and the number of fish sampled per site.
.........................................................................................................40
Table 8: Taxonomic designations of endoparasite types collected in the sGSL.
Abbreviations the first D represents the Class Digenea, the second
letter represents an arbitrary designation assigned during sorting to
differentiate between different species of digenea...........................45
Table 9: Abundance of each parasite species from 10 fish in each estuary. .....46
Table 10 Similarity matrix of the ectoparasite metacommunity presence/absence
data..................................................................................................74
Table 11:Table explaining the assignment of fish groupings in the ectoparasite
infracommunity dendogram (Figure 31). ..........................................79
Figure 38 The relationship between the number of endoparasites encountered
and the number of resource-based jobs near the estuary. ............106
vii
LIST OF FIGURES
Figure 1: Diagram representing the difference between Autogenic and Allogenic
parasite life cycles. ..........................................................................12
Figure 2: Diagrammatical representation of direct and indirect parasitic lifecycles:
(a) Direct lifecycle represented by Ergaslius sp. (Kabata 1988), (b)
Indirect lifecycle represented by simplified Lepocreadium setiferoides
lifecycle (Martin 1938)......................................................................13
Figure 3: Map of the southern Gulf of St. Lawrence (sGSL) with the estuaries
sampled marked with stars. .............................................................25
Table 4: Estuaries sampled, date of collection, GPS coordinates of each estuary,
and average water temperature and salinity at the time of sampling.26
Figure 4: Diagram illustrating bag beach seine sampling technique. Seine was
pulled into water following the basic pattern outlined above using the
following technique: (1) seine pulled into water from shore until the
bag first enters the water, (2) seine then pulled parallel to shore until
end of seine is reached, (3) seine is pulled back into shore to
complete the box-like pattern, and (4) both sides of the seine are
pulled onto the shore simultaneously (at a steady pace) trapping the
fish in the bag of the seine. ..............................................................27
Figure 5: Gill dissection (a) gill arch removal, (b) gill filament removal. .............29
Figure 6: Diagram of fish gut dissection. ...........................................................30
Figure 7: Monogenean specimen mounted in polyvinyl lactophenol, illustrating
the clearing properties of the medium..............................................32
Figure 8: Digenean specimens stained and mounted using (a) Borax-Carmine
alone, and (b) Borax-Carmine counterstained with Malachite
green.Both digeneans and cestoides were identified with the key by
Hoffman (1999). Three additional keys were also used for the
identification of digeneans; Schell (1985), Gibson (1996), and Schell
(1970). Tapeworms were identified using Schmidt (1970). .............33
Figure 9: Composite image of the different types of Gyrodactylus collected from
Cardigan River, PEI (a) Cg1-010731-006-Ga-L-Mg1-26, (b) Cg1010731-008-Ga-L-Mg1-27, (c) Cg1-010731-015-Ga-L-Mg1-29 and (d)
Cg1-010731-015-Ga-L-Mg1-31. ......................................................38
Figure 10: Plate illustrating features of Gyrodactylus sp. (a) Cg1-010731-006-GaL-Mg1-26 (circle outlines uterus containing larvae), (b) anterior of
worm with the two cephalic lobes, and (c) opisthaptor at the posterior
of the worm with marginal hooks and both hamuli visible. ...............39
Figure 11: Composite image of the copepod Ergasilus sp. (a) anterior region (9x),
(b) posterior region (9x), (c) first antennae and second antennae
modified for attachment, and (d) close up of modified second
antennae (45x).................................................................................42
Figure 12: Composite image of the copepod Thersitina gasterostei. (a) whole
mount, (b) antennae modified for attachment, and (c) modified legs.43
viii
Figure 13: Composite image of Brachyphallus crenatus (stained in Boraxcarmine) sampled from a G. aculeatus in PEI National Park estuary
(NP1-010814-001-Ga-G-DgA2). (a) whole mount of specimen (9x),
(b) close up of transverse annular plications (45x), (c) anterior
focused on oral and ventral suckers and presomatic pit (15x), (d) midbody with testes, ovaries and eggs (15x), (e) posterior with withdrawn
escoma (15x). ..................................................................................48
Figure 14: Digenean ‘B’ (a) whole mount of specimen NP1-010814-012-Ga-G-DB
(9x), (b) oral sucker (15x), (c) ventral sucker (15x), and (d) testes and
ovary (15x).......................................................................................50
Figure 15: Composite image of digenean ‘C’ (DC) (a) Whole mount (9x), (b)
margin of worm showing transverse annular plications (15x), (c)
Anterior third of body focused on oral sucker and anterior half of
ventral sucker (15x), (d) genital pore of uterus (15x). The specimen
was tentatively identified as a member of the family Lissochiidae. ..52
Figure 16: Composite images of digenean ‘D’ (Tentative identification as Family
Opecoelidae) focusing on important features (a) whole mount of
specimen NP3-010814-003-Ga-G-DgD (9x), (b) oral sucker (15x), (c)
ventral sucker and uterus containing eggs (15x), (d) testes and
ovaries (15x), and (e) excretory vesicle (15x). .................................54
Figure 17: Composite picture of Lepocreadium setiferoides sp. (DE) (a) whole
mount of specimen Co7-010718-013-Ga-G-DgE5, (b) spines on
margin of worm, (c) small ventral sucker posterior to oral sucker, (d)
eggs, ovary, testes and vitelline glands. ..........................................56
Figure 18: Major features of digenean ‘F’ (possible Subfamily Lecithasterinae) (a)
whole mount Co7-010718-023-Ga-G-DgF1, (b) oral and ventral
suckers, (c) testes, ovary and vitellarium, and (d) eggs. ..................58
Figure 19: Composite plate of digenean ‘G’ (Co7-010714-029-Ga-G-DgG1) (a)
whole mount (9x), (b) close up of ventral and oral suckers (15x), and
(c) close up of sac containing undetermined organs located near
ventral sucker (45x). ........................................................................59
Figure 20: Composite plate of digenean ‘J’ (C3-010726-009-Ga-G-DgJ1) (a)
whole mount specimen (9x), (b) close up of anterior region showing
large ventral sucker (15x), and (c) close up of muscular oral sucker
(45x).................................................................................................61
Figure 21: Composite picture of the various forms of digenean ‘K’, (a) Cg1010731-015-Ga-G-DgK1 (9x), (b) Cg1-010731-015-Ga-G-DgK2 (9x)
and (c) Cg1-010731-015-Ga-G-DgK3 (9x).......................................62
Figure 22: Picture of Hemiurus levinseni (DP) (a) whole mount of specimen RP2010912-002-Ga-G-DgP3 (9x), (b) annular plications (45x), (c) oral
sucker and ventral sucker (15x), (d) testes, ovary, vitellaria, uterus
and eggs (15x), (e) gonadopore and sinus sac (15x). .....................64
Figure 23: Composite picture of Podocotyle angulata (syn. P. staffordi) (DQ) (a)
whole mount of M4-010830-002-Ga-G-DgQ showing orientation of
testes and ovary (4x), (b) close up of tegument (10x), (c) close up of
ventral sucker (10x), and (d) position of gonadopore (in box) (10x).66
ix
Figure 24: Digenean ‘R' (a, b) illustrating the variety in body plan shapes, and (c)
vitelline gland (outlined in grey). ......................................................68
Figure 25: Composite picture plate of digenean ‘R' (DR) (Mg3-010821-002-Ga-GDgR2-2) (a) whole mount of specimen, (b) possibly the gonadopore
(in box) and (c) odd shaped unknown feature found in all specimens
(in oval). ...........................................................................................69
Figure 26: Cluster analysis dendogram illustrating the groupings of estuaries
based on the ectoparasite metacommunity total abundance similarity
matrix with the criteria for each divergence plotted on the dendogram.
Long dash (30%), Dot-long dash (60%), and squares (80%) lines
indicate levels of similarity. Abbreviations: Arg = Argulus sp., Tg =
Thersitina gasterostei, Erg = Ergasilus sp., Gyro = Gyrodactylus sp.
and ectos = ectoparasites. The estuary abbreviations are the same as
those appearing in Table 10. ...........................................................71
Figure 27: Non-metric Multidimensional Scaling (nMDS) plot of the groupings of
estuaries based on the ectoparasite metacommunity total abundance
similarity matrix. K=Kouchibouguac National Park, R=Richibucto,
Co=Cocagne, BV=Baie Verte, RP=River Phillip, T=Tatamagouche,
C=Caribou, Mg=Merrigomish, NP=PEI National Park, Cg=Cardigan,
and M=Murray Harbour....................................................................73
Figure 28: Cluster analysis dendogram illustrating the groupings of estuaries
based on the presence/absence similarity matrix with criteria for each
divergence plotted on the dendogram. Long dash (50%), Dot-Long
dash (70%), and squares (90%) lines indicate levels of similarity.
Abbreviations Tg – Thersitina gasterostei, Erg – Ergasilus sp., Gyro –
Gyrodactylus sp.. ............................................................................75
Figure 29: Non-metric Multidimensional Scaling (nMDS) plot of the groupings of
estuaries based on the ectoparasite metacommunity
presence/absence similarity matrix. .................................................76
Figure 30: Cluster analysis dendogram illustrating the groupings of individual fish
from the different estuaries based on the ectoparasite infracommunity
similarity matrix. Three levels of similarity are also plotted on the
dendogram95%=small squares, 70%=long dash and dot, 40%=long
dash. G1 through seven outline major groupings of fish based on the
types of parasites present (Table 12). .............................................78
Table 11:Table explaining the assignment of fish groupings in the ectoparasite
infracommunity dendogram (Figure 31). ..........................................79
Figure 31: Non-metric Multidimensional Scaling (nMDS) plot of the ectoparasite
infracommunity analysis with three similarity levels 95%=small
squares, 70%=long dash and dot, 40%=long dash used to delineate
the groupings of the estuaries..........................................................80
x
Figure 32: Cluster analysis dendogram illustrating the groupings of estuaries
based on the endoparasite metacommunity total abundance similarity
matrix with the breakage points plotted on the dendogram.
Abbreviations: DA=Brachyphallus crenatus, DB=digenean ‘B’,
DC=digenean ‘C’, DD=digenean ‘D’, DE=Lepocreadium setiferoides,
DF=digenean ‘F’, DJ=digenean ‘J’, DK=digenean ‘K’, DP=Hemiurus
levinseni, Nm=Nematodes, Nmcy=Nematode cysts, K=Kouchibouguac
National Park, R=Richibucto, Co=Cocagne, BV=Baie Verte, RP=River
Phillip, T=Tatamagouche, C=Caribou, Mg=Merrigomish, NP=PEI
National Park, Cg=Cardigan, and M=Murray Harbour. ....................82
Figure 33: Non-Metric Multidimensional Scaling (nMDS) Plot of the endoparasite
metacommunity total abundance similarity matrix information.
K=Kouchibouguac National Park, R=Richibucto, Co=Cocagne,
BV=Baie Verte, RP=River Phillip, T=Tatamagouche, C=Caribou,
Mg=Merrigomish, NP=PEI National Park, Cg=Cardigan, and
M=Murray Harbour...........................................................................83
Figure 34: Cluster analysis dendogram illustrating the groupings of estuaries
based on the endoparasite metacommunity presence/absence
similarity matrix. Abbreviations: DA=Brachyphallus crenatus,
DB=digenean ‘B’, DC=digenean ‘C’, DD=digenean ‘D’,
DE=Lepocreadium setiferoides, DF=digenean ‘F’, DJ=digenean ‘J’,
DK=digenean ‘K’, DP=Hemiurus levinseni, Nm=Nematodes,
Nmcy=Nematode cysts, K=Kouchibouguac National Park,
R=Richibucto, Co=Cocagne, BV=Baie Verte, RP=River Phillip,
T=Tatamagouche, C=Caribou, Mg=Merrigomish, NP=PEI National
Park, Cg=Cardigan, and M=Murray Harbour. ..................................85
Figure 35: Non-Metric Multidimensional Scaling (nMDS) Plot of the endoparasite
metacommunity presence/absence similarity matrix
information.K=Kouchibouguac National Park, R=Richibucto,
Co=Cocagne, BV=Baie Verte, RP=River Phillip, T=Tatamagouche,
C=Caribou, Mg=Merrigomish, NP=PEI National Park, Cg=Cardigan,
and M=Murray Harbour....................................................................86
Figure 36: Detrended Correspondence Analysis (DCA) plot of endoparasite
infracommunity (e.g. Nm = Nematodes) and fish hosts (e.g. BV7 =
fish #7 from Baie Verte), with and envelope encompassing the
individual fish hosts that contain that specific parasite species. Lines
illustrate the occurrences and overlapping of the different parasite
species (Dot-long dash=DA, Long dash=DD, solid=DE, squares=DP,
and short dash=Nm). Parasite species abbreviations: DA =
Brachyphallus crenatus, DD = digenean ‘D’, DE = Lepocreadium
(setiferoides) sp., DP = Hemiurus levinseni, Nm = Nematodes. ......88
xi
Figure 37: Detrended Correspondence Analysis (DCA) plot of endoparasite
infracommunity (e.g. Nm = Nematodes) and fish hosts (e.g. BV7 =
fish #7 from Baie Verte), with and envelope encompassing the
individual fish hosts that contain that specific parasite species.
Abbreviations DA = Brachyphallus crenatus, DB = digenean ‘B’, DD =
digenean ‘D’, DE = Lepocreadium (setiferoides) sp., DF = digenean
‘F’, DK = digenean ‘K’, DP = Hemiurus levinseni, Nm = Nematodes.
Outlined areas show contents of indicated areas of highly
concentrated points. ........................................................................89
Figure 38 The relationship between the number of endoparasites encountered
and the number of resource-based jobs near the estuary. ............106
xii
CHAPTER 1
GENERAL INTRODUCTION
Understanding the biodiversity of the parasites of the three-spine
stickleback (Gasterosteus aculeatus) in the southern Gulf of St. Lawrence
(sGSL) is an important step in understanding the sGSL ecosystem. Because
the complex lifecycles of parasites are integrated into the intricate food webs
of the ecosystem, parasites can be viewed as a link between the various
trophic levels. Parasites can therefore be utilized as indicators of trophic
ecology, structure of food webs, food preference and the foraging mode of the
host (Brooks & Hoberg 2000). Understanding parasites in the ecologicaltrophic context can help increase knowledge in many areas including: a host’s
trophic position in a food web; the use and potentially the amount of time
spent in different microhabitats, if parasites are being picked up via host
switching, and therefore what hosts may be in direct competition; the impact
of a parasite on a host; a host’s diet changes throughout its lifecycle; and the
potential migratory nature of hosts (Brooks & Hoberg 2000). These
characteristics could enable a greater understanding of the ecosystem as a
whole and therefore enable more effective monitoring and protection of that
environment.
1.1.
Parasites as bioindicators in ecological assessment
Researchers have considered the use of parasites as bioindicators for
assessment of specific ecological systems for the last fifty years. In 1958,
Wisniewski examined the characteristics of the parasitofauna of Druznno
1
Lake, Poland, primarily to see if the parasitofauna of that lake could be used
to determine the eutrophic status of a lake. Eutrophication, pollution, and
habitat fragmentation have been examined to determine their effects on
parasite communities in roach (Rutilus rutilus) and perch (Perca fluviatilis) in
lakes in Finland (Valtonen et al. 1997). However, the results from these
studies were inconclusive due to the high variability in parasite communities.
The potential for parasites to identify different stocks of fish for monitoring
programs has also been examined. Scott (1969) attempted to use trematode
populations of the Atlantic argentine (Argentina silus) as biological indicators,
however he was unable to find a difference in parasite loads of from different
areas. Pálsson (1986) performed quantitative studies on the helminth fauna of
capelin (Mallotus villosus) and determined that some parasites could be used
to discriminate among capelin stocks. He suggested that the use of parasites
as ecological assessment monitors and for stock discrimination needs more
study.
1.2 Background to the present study
This project developed as a component of the Biodiversity of Stickleback
Parasites DIVERSITAS-International Biodiversity Observation Year (IBOY)
project (Loreau & Olivieri, 1999). The biodiversity projects seek to develop
effective surveys and inventories that will link biological communities to
significant environmental and socioeconomic issues (Brooks & Hoberg, 2000).
Surveys are being conducted on a wide variety of taxonomic groups, and
range from reorganizing museum collections (Allison, 2003) to coral reef
surveys (Mikkelsen & Cracraft, 2001).
2
The biodiversity study of the parasites of sticklebacks is examining
parasitic fauna of a variety of stickleback species, and is led by Dr. David J.
Marcogliese (St. Lawrence Centre, Environment Canada, Montreal, Quebec).
The core species in this study is the three-spine stickleback; they are one of
the most widely studied species of fish, primarily due to their circumpolar
distribution, hardiness and ease of capture (Wootton 1976). In Canada,
three-spine stickleback are being studied in Newfoundland (NL), New
Brunswick (NB), Quebec (QC), Ontario (ON), Manitoba (MN), Alberta and
British Columbia (BC). Understanding the parasites of the three-spine
sticklebacks could facilitate a greater understanding of the sGSL ecosystem
as a whole and therefore enable a more valuable monitoring and protection
protocol of the area.
1.3 Study Area
The present study focused on estuarine environments in the sGSL
(southern Gulf of St. Lawrence). These estuaries differ significantly from the
neighbouring estuaries within the Bay of Fundy between southern New
Brunswick and southeastern Nova Scotia. The sGSL is dominated by
estuaries and protected embayments, and is typical of Atlantic coastal
systems found south of Cape Cod, Massachusetts (MA). The sGSL supports
a warm water relict fauna that is similar to those of areas farther south, but
have adapted to the freeze-over conditions in the winter (Bousfield and
Laubitz 1972, Burtness 1999). Eleven estuaries were sampled, throughout
the summer, from New Brunswick (NB), Nova Scotia (NS) and Prince Edward
3
Island (PEI) to compare the parasite fauna of sticklebacks from a diverse
range of locations and estuarine habitats.
1.3.1 Previous studies in this area
There have been no equivalent studies on the parasites of three-spine
sticklebacks in the southern Gulf of St. Lawrence. A preliminary phase of this
project was initiated in the Kouchibouguac River Estuary in Kouchibouguac
National Park, NB in 2000-2001. This study examined the use of parasites in
detecting the post-glaciation migratory path of the three-spine stickleback in
the sGSL (Peddle 2001). Three sites, spanning the estuary’s salinity gradient
were sampled within each estuary once per month from May through August.
Six types of parasites were collected from gut samples: three digenean
species (Podocotyle atomon (tentative identification), Creptotrema funduli,
and Brachyphallus crenatus), two Cestode species (Proteocephalus filicollis
and Bothriocephalus scorpii), and one unidentified Nematode. These results
were used to examine possible local, seasonal, migratory paths, as well as
attempt to identify the post glaciation migratory path of G. aculeatus.
Although there has been little research on the parasites of G. aculeatus in
the sGSL, on parasites of other fish species in the area have been
documented. These studies have focused on economically important fish.
Hogans (1984) examined the parasites of striped bass (Morone saxatilis) in
Kouchibouguac River Estuary (Kouchibouguac National Park). Frimeth
(1987a) formed a survey of the parasites of anadramous and nonanadromous brook char (Salvelinus frontinalis) in the Tabusintac River, New
Brunswick, which is located to the north of Kouchibouguac National Park. In
4
1975, Scott examined the incidence of digenean parasites and its potential
relationship with fish length and food eaten by the American plaice
(Hippoglossoides platessoides) populations from the Scotian Shelf and
southern Gulf of St. Lawrence. Scott (1982) also looked at the digenean
communities in other flatfish species of the Scotian Shelf and the sGSL. He
took an ecological approach to parasitology, focusing on parasitocoenosis.
Parasitocenosis is the concept that different species of parasites in a host
comprise a community, and that the parasites are representative of both the
macroenvironment in which the host lives and the microenvironment (host)
where the parasite lives (Scott 1982). The activity and physiological changes
in the host and the availability of intermediate host(s) influence the
macroenvironment. When the behaviour and physiology of the host changes,
the microenvironment within the host changes, and affects the development
and survival of parasites (Scott 1982).
McGladdery and Burt (1985) worked in the Gulf of St. Lawrence and
examined the parasites of the North Western Atlantic herring (Clupea
harengus). They were looking for potential bioindicators of the herring’s
migration, feeding and spawning patterns. They found that, of the eighteen
parasites identified from the North Western Atlantic herring, there was no
single parasite that could clearly identify one population from another.
However, when they examined differential prevalences and intensities of
seven different parasite species (Anisakis simplex, Hysterothylacium
aduncum, Derogenes varicus, Lecithaster gibbosus, Cryptocotyle lingua,
Scole pleuronectis, and Eimeria sardinae) they found that these distributions
provided valuable information on the North Western Atlantic herring’s
5
migration. Arthur and Albert (1994) performed a similar survey of the
zooeogeography of the parasites in the Greenland halibut (Reinhardtius
hippoglossoides) caught off the Atlantic coast.
1.4 Statement of Problem
This project was designed to identify the types of parasites that are found
on and in G. aculeatus in the sGSL, and to determine whether or not G.
aculeatus populations in adjacent estuaries share ecto- or endoparasites. An
additional objective was to investigate whether or not parasite communities
within populations of G. aculeatus could be used as indicators of
environmental status.
1.5 Objectives and organization of thesis
1.5.1 Objectives
The main objectives of the thesis were to:
a) describe the parasites of G. aculeatus in the southern Gulf of St.
Lawrence (sGSL),
b) compare parasite communities of G. aculeatus on two different levels
i.
at the metacommunity level, to compare parasite communities
among adjacent geographic areas, and
ii.
at the infracommunity level, compare how individual fish parasite
communities within a single estuary, and
6
c) evaluate use of parasite communities within populations of G.
aculeatus be used as indicators of environmental status.
1.5.2 Hypotheses
The initial part of the thesis work was aimed at documentation of the
parasite communities found within the three-spine sticklebacks populations
studied. After this preliminary study was completed, the primary null
hypothesis was formulated that the infracommunities within a single estuary
are the same. At the metacommunity level, comparing parasite communities
between estuaries, the null hypothesis that there is no difference between the
estuaries.
1.5.3 Organization of the Thesis
Following a traditional thesis format, the General Introduction is followed
by a secondary introductory chapter (Chapter 2), which describes
Gasterosteus aculeatus and the primary parasites of interest. Chapter 3
outlines the materials and methods of this project, including how the
estuaries, the fish and the parasites were sampled, as well as identification
and analysis techniques. Chapter 4 provides the results of the thesis,
including description of the parasites found in each estuary and their
abundance. The results include the Detrended correspondence analysis
(DCA), Cluster and non-metric multidimensional scaling (nMDS) results from
the community ecology analyses. The discussion (Chapter 5) weighs both the
biodiversity and community ecology results.
7
Chapter 2
Overview of the geographic distribution and biology of the host and
parasites
This chapter provides a general introduction to the fish species under
study, and to the life cycles and characteristics of its major parasite groups of
interest.
2.1 Geographic distribution of the three-spine stickleback
The three-spine stickleback (Gasterosteus aculeatus) is a member of the
Family Gasterosteidea (Wootton 1976). Three-spine stickleback were first
described by Linneaus in Europe in1758 (Lee et al. 1980). The Family
Gasterosteidea has a distribution that is restricted to temperate and sub-polar
zones of the northern hemisphere. In North America, the family includes four
other stickleback species: (i) G. wheatlandi, the black-spotted stickleback; (ii)
Apeltes quadracus, the four-spine stickleback; (iii) Pungitius pungitius, the
nine-spine stickleback; and (iv) Culea inconstans, the brook stickleback
(Wootton 1976). Three-spine stickleback is the only member of
Gasterosteidea that can tolerate marine, brackish and freshwater conditions,
and are therefore considered to be euryhaline (Wootton 1976).
Three-spine stickleback have a nearly circumpolar distribution and are
widely distributed throughout both marine and freshwater environments of the
northern hemisphere (Lee et al. 1980). It is found between 35oN and 70oN in
Europe, North America and parts of Asia, however it is absent from Africa
(Wootton 1976). On the Atlantic coast of North America, three-spine
8
stickleback are distributed from Chesapeake Bay to Hudson Bay and Baffin
Island. Freshwater populations are found relatively far inland, especially in
Maine and New Brunswick. They are found throughout Lake Ontario as well
as the in Ottawa and St. Lawrence Rivers (Lee et al. 1980).
2.2 Biology of the three-spine stickleback
Three-spine stickleback generally grow to be no larger than 30-75mm in
length (Lee et al. 1980). They lack scales and instead have rows of bony
lateral plates (scutes). It is thought that there are at least three different forms
of three-spine stickleback, and that one distinguishing feature is the number of
lateral plates. The anadramous form trachurus contains a full set of
approximately thirty to thirty-five lateral plates that are arranged from just in
front of the pectoral fin to the tail. They also possess a keel on their caudal
peduncle (Wootton 1976). Trachurus stickleback normally have silverycoloured bodies, however during the breeding season the, males develop
bright blue-coloured eyes and a red-coloured belly (Wootton 1976).
Because of their anadromous nature, three-spine stickleback migrate into
fresh and brackish waters to breed. A male builds and protects a nest from
eelgrass and lure females to the nest to lay their eggs in it (Wootton 1976).
The male then protects the eggs from predators, like other sticklebacks, until
they hatch. In the autumn, the young-of-the-year and any remaining adults
migrate back into marine areas where they overwinter (Wootton 1976).
Three-spine stickleback are most commonly found in slow-flowing back
waters and tributaries of rivers, as well as in ditches, dykes and in sheltered
bays or harbours. They are also common in lakes or ponds where they can
9
be found among areas of emergent or submerged rooted vegetation. They are
not found in steep, fast-flowing streams, and are therefore rare or absent in
mountainous regions (Wootton 1976, Lee et al. 1980).
2.3 Major parasites being considered in this study
Parasites can be classified by the ecosystem in which they live, the
location on their host and their life cycle (Table 1). Parasitic ways of life
involve either single (autogenic) or multiple (allogenic) ecosystems (Figure 1).
This study focused on the autogenic ecosystem where the parasites complete
their entire lifecycle within a single ecosystem, in this case an aquatic
ecosystem. Allogenic parasites are those parasites that utilize two or more
ecosystems to complete their lifecycle (Esch and Fernández 1993).
10
Table 1 General life history characteristics of the different parasites discussed in this paper (Roberts and Janovy 1996, Hoffman
1999) * (See Figure 2)
Group
Life Cycle*
Intermediate Host
Monogenea
Direct
None
Copepoda
Direct
None
Digenea
Indirect
Cestoidea
Indirect
Acanthocephala
Indirect
1 or more generally copepod,
mollusc, or some
other type of
arthropod
1 or more generally copepod,
mollusc, or some
other type of
arthropod
1 or more generally copepod,
mollusc, or some
other type of
arthropod
Dispersion
Requirements
variable - range
from none (freeswimming larvae) to
fish-fish contact
variable - generally
free-swimming larval
stage finds new host
variable generally consumption
of intermediate host
Intermediate Life Stage
Mobility
variable E.g. High - larvae
(oncomiracidium) swims to
find new host
variable generally consumption
of intermediate host
variable - generally low
variable generally consumption
of intermediate host
variable - generally low
variable - generally high
variable - generally low
(occasionally high with freeswimming larvae that burrows
into definitive host)
11
Autogenic
=
aquatic
ecosystem
Allogenic
= aquatic +
terrestrial
ecosystems
Figure 1: Diagram representing the difference between Autogenic and Allogenic
parasite life cycles.
Parasites can also be classified as external (ectoparasites) or internal
(endoparasites). Ectoparasites generally have a direct lifecycle (Figure 2) where the
parasite requires only a single host, known as the definitive or final host, to complete
its lifecycle. The parasite reaches sexual maturity on the definitive host, and the rest
of the lifecycle stages are spent as free-living larvae (Esch and Fernández 1993).
Endoparasites typically have an indirect lifecycle (Figure 2), requiring two or more
hosts to complete the parasite’s lifecycle. Intermediate hosts are usually molluscs or
copepods but this is parasite-dependent; there may be more than one intermediate
host in the lifecycle (Esch and Fernández 1993). The parasite reproduces asexually
and develops in the intermediate host but not to sexual maturity.
12
On
Gills &
Body
Definitive Host
Definitive Host
EGG
2 nd Intermediate Host
(a)
1st Intermediate Host
(b)
Free swimming
stage to mate
Free swimming stage
Figure 2: Diagrammatical representation of direct and indirect parasitic lifecycles: (a)
Direct lifecycle represented by Ergaslius sp. (Kabata 1988), (b) Indirect lifecycle
represented by simplified Lepocreadium setiferoides lifecycle (Martin 1938).
2.3.1 Ectoparasites
The two major ectoparasitic groups encountered in the Gulf of St. Lawrence are
monogenic trematodes and copepods. Common endoparasites encountered include
digenic trematodes, cestodes and acanthocephalans.
2.2.1.1 Phylum Platyhelminthes, Class Mongenea (Monogenic Trematodes)
The group Monogenea includes hermaphroditic flatworms that occur primarily on
the gills and external surfaces of fish. They are rarely regarded as a threat to fish
health under natural conditions; however, they can have a serious effect on fish
health in hatchery settings where fish are reared in highly crowded conditions
(Roberts & Janovy 1996).
Monogeneans are generally bilaterally-symmetric. Their body is usually
colourless or grey and can be roughly divided into three regions: the cephalic region
13
anterior to the pharynx, the body or trunk, and the posterior attachment organ or
opisthaptor (Roberts & Janovy 1996). Eggs, internal organs or food that has been
ingested may provide some monogeneans with colour. Monogeneans vary in size
from 1.03 to 10.0 mm in length, with marine forms usually being larger than
freshwater forms.
The life cycle for monogeneans is not well-known, except for those of a few
species; notable species of the genus Gyrodactylus. However, it is known that
monogeneans generally, have a direct lifecycle, (i.e. no intermediate hosts are
involved) including stages as egg, oncomiracidium larva and adult. When the
oncomiracidium hatches from the egg, it has cilia that enable it to swim until a host is
found. Once it comes into contact with a host and attaches to it, the oncomiracidia
loses its ciliated cells and develops into an adult (Roberts & Janovy 1996). Although
this is the case for most monogeneans, there are some exceptions. For example,
the Gyrodactylidae are viviparous: the young remain in the uterus until they develop
into functional sub-adults. Another unique characteristic of Gyrodactylidae
development is what can be termed as sequential polyembryony. A juvenile
develops inside the adult, with a subsequent juvenile developing within it, and there
can even be a third juvenile with a fourth juvenile developing inside it. Therefore,
usually four individuals can be created from one zygote (Roberts & Janovy 1996).
Once the young worm is born, it begins to feed on its host and then gives birth to the
juvenile remaining inside. It is then that an egg from its own ovary can be fertilized
to repeat the process. Generally the time period from birth to maturation is one day
(Roberts & Janovy 1996).
14
2.2.1.2 Phylum Arthropoda, Class Crustacea, Order Copepoda
The Order Copepoda consists of both free-living and parasitic forms. The
parasitic forms are known to infect freshwater, brackish and marine fishes.
The parasitic members of this subclass range from highly- to barely-modified
(Hoffman 1999). There are some general adaptive trends in parasitic copepods,
including a modification of appendages, e.g. reduction in the size of those used in
locomotion, modification of appendages for attachment to the host, reduction of the
sense organs, and development of new structures. There is also a change in body
proportion and segmentation, with parasitic copepods generally having larger genital
and reproductive regions, as well as less external evidence of segmentation. Finally,
there is a reduction in the number of free-living instars, by developing past more
stages before hatching and having parasitic larval instars (Hoffman 1999).
In general, the parasitic copepod lifecycle progresses through indirect
development. A distinguishable nauplius larval stage hatches from the egg,
generally with three pairs of appendages it progresses through several ecdyses in
order to add somites and appendages with each molt. Of these different instars, the
later ones may be called metanauplii (Hoffman 1999). The metamorphosis of nauplii
may be gradual, and occur over several instars, or be abrupt from one instar to the
next. Through these various instars, the nauplius develops into an adult. With direct
development, a juvenile hatches from the egg, not a nauplius larva. Juvenile are
distinguished from the larva because they hatch complete with segmentation and
appendages, however the juvenile are sexually immature and must develop into the
adult form before becoming reproductive (Hoffman 1999).
15
2.3.2 Endoparasites
2.2.2.1 Phylum Platyhelminthes, Class Digenea (Digenetic Trematodes)
The digenetic trematodes belong to the class Digenea, and are generally
hermaphroditic. Digeneans parasitize all classes of vertebrates, especially fishes,
and can be found in almost every organ of the vertebrate body (Roberts & Janovy
1996). Digeneans appear to cause little to no harm to the host (Hoffman 1999).
The general digenetic trematode’s body is dorsoventrally flattened and oval in
shape. It usually has a powerful oral sucker that surrounds the mouth as well as a
ventral sucker or acetabelum that is usually located midventrally. However, not all
digeneans follow this basic body plan; there can be a great variety in the size, shape,
presence or absence of various organs, making these organs an important
identification tool. Digeneans can range in size from 0.16 mm to about 5.7 cm in
length. The presence and location of the suckers is one of the identifying
characteristics of digenetic trematodes. A monostome digenean has only an oral
sucker; an amphistome digenean has an oral sucker and an acetubelum at the
posterior end of the body. The distome digenean has an oral sucker and the
acetabelum elsewhere on the ventral surface (Roberts & Janovy 1996). Other major
identifying characteristics are the shape and orientation of the caeca, excretory
vesicle, ovaries, testes & vitelline glands (Schell 1970). The orientation of the
gonadopore and the cirrus sac, if present, are also very important in the identification
of digeneans (Schell 1970)
16
The digenean lifecycle consists of at least two different hosts; an intermediate
host and a definitive host (Roberts & Janovy 1996). In general, the life cycle of a
digenean trematode progresses from a ciliated miracidium, which is a free-swimming
larva that hatches from its shell and penetrates the first intermediate host, usually a
snail. Generally, at this point, the larva sheds its ciliated epithelium and
metamorphoses into a sporocyst, a simple, sac-like form in which a number of
embryos develop asexually to become rediae (Roberts & Janovy 1996). Rediae
larvae have a slightly greater differentiation than the sporocyst stage, possessing
both a pharynx and gut. Within the rediae, additional embryos develop called
cercariae. The cercarial stage emerges from the intermediate host, often with a tail
to aid in swimming (Roberts & Janovy 1996). Although cercariae are considered
juveniles, many species still require a metacercarial stage before they are infective to
the definitive host. The metacercarial stage usually encysted. The definitive host
becomes infected when it ingests an intermediate host carrying metacercariae
(Roberts & Janovy 1996).
2.2.2.2 Phylum Platyhelminthes, Class Cestoidea
Tapeworms are members of Class Cestoidea and Phylum Platyhelminthes.
Mature tapeworms can be found in all classes of vertebrates generally in the
intestine or its digestive diverticulae (Schmidt 1970). They are commonly found in
natural fish populations and occasionally found in cultured fish stocks (Roberts and
Janovy 1996).
The tapeworm body plan consists of three distinct regions: the scolex, the neck
and the strobila. The scolex is the head or holdfast organ of the tapeworm and is
17
found at the anterior end of their body. Its function is to maintain the position of the
tapeworm in the gut of the host (Roberts and Janovy 1996). Therefore the scolex
may have suckers, grooves, hooks, spines, glands, tentacles, or a combination of
these most tapeworms posses a scolex. There are, however, some cestodes that
lose their scoleces early in life. In these species the anterior end of the body
becomes a pseudoscolex to perform the function of the lost scolex (Roberts and
Janovy 1996).
There are three main sucker-like organs that can be found on the scoleces of
tapeworms: acetabula, bothridia and bothria. Acetabula are usually present as four
suckers evenly distributed around the scolex. These suckers are essentially cupshaped or approximately circular and outlined with a heavy muscular wall (Roberts
and Janovy 1996). Bothridia are usually present in groups of four as well. They are
muscular projections extending from the scolex and can have highly mobile leaf-like
margins. Finally, when present, there are usually two bothria on the scolex however
there can be as many as six. They appear as shallow pits or long grooves that are
arranged in dorsoventral or lateral pairs (Roberts and Janovy 1996). In addition to
the main sucker types, accessory suckers can also be present. Proteinaceous
hooks also aid in anchoring the worm. When present in acetabulate worms, the
hooks are generally arranged on the rostellum, a protrusible, dome-shaped area at
the apex of the scolex. The presence or absence, shape and arrangement of the
hooks are important taxonomic tools (Roberts and Janovy 1996).
18
The scolex also contains the chief neural ganglia. This is an area on the anterior
surface with numerous sensory endings. It is thought to enable the tapeworm to find
an optimal placement for the scolex (Roberts and Janovy 1996).
The neck is the commonly found between the scolex and the strobila. It is a
relatively undifferentiated area and can be either long or short. The neck contains
stem cells, which are apparently responsible for giving rise to new proglottids. If
there is no neck present, similar cells can be found in the anterior end of the scolex
(Roberts and Janovy 1996).
The strobila is a linear series of reproductive organs, for both sexes, contained
within proglottids (Roberts and Janovy 1996); a proglottid is a segment that contains
the gonads (Hoffman 1999). Strobilation, the production of new proglottids, occurs
near the anterior end of the worm. As new proglottids are produced the older
proglottids move towards the end of the worm and become sexually mature. The
proglottids closest to the posterior have already copulated, with itself, others in the
strobila or other worms, and produced eggs (Roberts and Janovy 1996). Proglottids
that contain fully developed eggs or shelled embryos are considered gravid.
Although species-dependant, a gravid proglottid detaches when it reaches the end of
the strobila, and is either passed with the feces, or degenerates and releases the
eggs (Roberts and Janovy 1996).
Cestodes generally have an indirect life cycle that includes both intermediate and
definitive hosts. Mature tapeworms can live for a few days or up to ten years, and
during that time can produce a few to millions of eggs. The tapeworm develops
through different larval stages, but does not reach sexual maturity in an intermediate
19
host (Schmidt 1970). Intermediate hosts can be both invertebrate and vertebrate;
the intermediate host is part of the diet of the definitive host. Crustaceans, annelids
and molluscs are some of the more common intermediate host types (Schmidt
1970).
2.2.2.3 Phylum Acanthocephala
Members of Phylum Acanthocephala mainly infect fish, birds and mammals.
They can occur in both aquatic and terrestrial host. Adult worms are found in the
digestive tract of the definitive host (Arai 1989).
Acanthocephalans are bilaterally symmetrical slender, cylindrical (or slightly
flattened) and hollow worms. Their main diagnostic feature is the invaginable
proboscis found on the anterior end (Arai 1989). The proboscis is armed with rows
of recurved hooks and is used for attachment. The number, shape and arrangement
of hooks is very important for the proper identification of members of this Phylum
(Arai 1989). The armed proboscis, which the worm uses for attachment to the hosts
intestinal wall, can inflict serious harm to the host. As the worm changes location in
the intestine it retracts and reinserts the proboscis in a new location, when many
acanthocephala infect an individual host this can cause serious intestinal lesions in
that host.
Acanthocephalans are usually dioecious, and at least two worms of opposite
sexes are required per host to have a reproductively viable community.
Acanthocephalans can be sexually dimorphic, with the female being the larger of the
two (Arai 1989). The female produces eggs with embryos that are partially
20
developed (acanthors), which are relaeased into the host intestinal lumen. They
complete embryo development within the egg as they are shed from the host. An
invertebrate host, usually a copepod, ostracod, amphipod or isopod, is required for
hatching and development of the larvae. The first intermediate host is always an
arthropod, but fish can act as a second intermediate host for those
acanthocephalans with definitive hosts that are aquatic mammals or birds (Arai
1989).
2.3.3 Relevant Literature
Over the past 100 years, scientific literature reports 13 ectoparasites on G.
aculeatus in Canada: seven Monogenea, one Branchiurian and six Copepoda have
been documented (Table 2).
Further, literature from the same time period reported 19 endoparasites in G.
aculeatus throughout Canada (Table 3). Fifteen of these were members of Class
Digenea, and seven each were members of Class Cestoidea and Phylum
Acanthocephala.
21
Table 2: Ectoparasite records found from the literature (Beverley-Burton 1984, Kabata 1988, Rafi 1988, Bousfield & Kabata
1988). 1 denotes that the parasite was found and 0 denotes no report. Abbreviations: AT=Atlantic Ocean,
NL=Newfoundland and Labrador, NS=Nova Scotia, NB=New Brunswick, PEI=Prince Edward Island, QC=Quebec,
ON=Ontairo, MN=Manitoba, BC=British Columbia, NT=North West Territories, YK=Yukon Territory, PC=Pacific Ocean,
Mg=Monogenea, B=Branchiura, Cp=Copepoda.
PARASITES
Mg Dactylogyrus sp
Mg Gyrodactylus alexandria
Mg Gyrodactylus avalonia
AT
0
0
1
NL
0
0
1
NS
0
0
1
NB
0
0
1
PEI
0
0
0
QC
0
0
1
ON
0
0
1
MN
0
0
0
BC
1
1
0
NT YK PC
0
0
0
0
0
1
0
0
0
Mg
Gyrodactylus canadensis
1
1
0
0
0
1
0
0
0
0
0
0
Mg
Gyrodactylus lairdi
0
1
0
0
0
0
0
0
0
0
0
0
Mg
Gyrodactylus momorialis
0
1
0
0
0
0
0
0
0
0
0
0
Gyrodactylus terranovae
Gyrodactylus sp
Argulus stizostethi
Bomolochus cuneatus
Caligus clemensi
Ergasilus auritus
Ergasilus turgidus
Lepophtherius sp.
Cp Thersitinia gasterostei
0
0
0
0
0
0
0
0
1
1
0
1
0
0
1
0
0
1
0
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
1
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
0
0
1
1
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
0
Mg
Mg
B
Cp
Cp
Cp
Cp
Cp
22
Table 3: Parasites from the literature of Gasterosteus aculeatus in Canada. 1 denotes that the parasite was found, 0 denotes
no record. Provincial abbreviations as in Table 2, parasite abbreviations: D=Digenea, T=Cestoidea, A=Acanthocephala.
D
D
D
D
D
D
D
D
D
D
D
D
D
T
T
A
A
A
A
PARASITES
Allobunodera mediovitellaria
Branchyphalus crenatus
Bunodera luciopercae
Bunoderina eucaliae
Crepidostomum cooperi
Crepidostomum faarionis
Derogenes varicus
Lecithaster gibbosus
Parahemiurus merus
Podocotlye angulata
Podocotlye atamon
Podocotlye sinusacca
Podocotlye reflexa
Proteocephalus fillicollis
Proteocephalus pungetensis
Echinorhynchus lateralis
Echinorhynchus salmonis
Neoechinorhynchus rutili
Pomphorhynchus bulbocolli
NL NS NB PEI QC ON MN BC NT YK
1
0
0
0
1
1
0
1
0 0
1
1
1
1
1
0
0
1
1 1
1
0
0
0
1
1
0
1
0 0
0
0
0
0
1
1
0
1
0 0
1
1
1
1
1
1
1
0
0 0
1
1
1
1
1
1
1
1
1 1
1
1
1
0
1
0
0
1
1 0
1
1
1
0
0
0
0
1
1 0
0
0
0
0
0
0
0
1
0 0
1
0
1
0
0
0
0
0
0 0
1
0
0
0
1
0
0
0
0 0
0
0
0
0
0
0
0
1
0 0
1
0
0
0
0
0
0
0
0 0
1
0
0
0
0
0
1
0
0 0
0
0
0
0
0
0
0
1
0 0
1
0
1
0
1
1
0
0
0 0
0
0
0
0
1
1
1
0
1 0
1
0
1
0
0
1
0
1
1 1
0
0
0
0
1
1
1
1
0 0
23
Chapter 3
Materials and Methods
3.1 Study sites
Estuaries along the Gulf of St. Lawrence contain prime breeding grounds for
three-spine stickleback due to the presence of eelgrass (Zostera spp.). Three-spine
stickleback collected along the Gulf of St. Lawrence coastline appear to be of the
trachurus form and are a euryhaline and anadramous species (Wootton 1976).
The sites sampled all had similar basic characteristics; being selected based on
the presence of eelgrass, relatively shallow water (<1.6 m) and the presence of a
stable substrate. Four estuaries were sampled in New Brunswick (NB):
Kouchibouguac National Park (KNP), Richibucto (R), Cocagne (Co), and Baie Verte
(BV). Four estuaries were also sampled in Nova Scotia: River Phillip (RP),
Tatamagouche (T), Caribou (C), and Merrigomish (Mg). Three estuaries were
sampled in Prince Edward Island (PEI): PEI National Park (NP), Cardigan (Cg), and
Murray Harbour (M) (Figure 3, Table 1).
24
K.N.P.
Richibucto
P.E.I.N.P.
P.E.I.
Cardigan
Cocagne
Murray
Harbour
New
Brunswick
Baie Verte
River Philip
Tatamagouche
Caribou
Merrigomish
Nova Scotia
Figure 3: Map of the southern Gulf of St. Lawrence (sGSL) with the estuaries sampled marked with stars.
25
Table 4: Estuaries sampled, date of collection, GPS coordinates of each estuary, and average water temperature and
salinity at the time of sampling.
Province
Estuary
Abbreviation
Date
GPS
(N)
New
Brunswick
Nova
Scotia
P.E.I.
Kouchibouguac
National Park
Richibucto
K
5-Jul-01
R
8-Jul-01
Cocagne
Co
11-Jul-01
Baie Verte
BV
19-Jul-01
River Philip
RP
12-Sep-01
Caribou
C
26-Jul-01
Tatamagouche
T
24-Jul-01
Merrigomish
Mg
21-Aug-01
P.E.I. National Park
NP
14-Aug-01
Cardigan
Cg
1-Aug-01
Murray Harbour
M
30-Aug-01
46
50.206
46
41.835
46
20.31
46
3.12
45
51.16
45
44.00
45
44.13
45
36.81
45
39.4
45
19.23
46
22.94
GPS
(W)
Salinity
‰
64
55.953
64
45.423
64
34.412
64
4.92
63
44.05
62
40.24
36
15.13
62
30.93
61
50.31
66
1.18
62 6.6
30.9
Water
Temperature
°C
17.6
32.1
17.3
34.1
21.8
31.6
23.7
24.8
21.3
29.4
21
37.4
23.5
29.9
24.3
26.5
24.9
32
24.5
27.4
21.8
26
3.2 Sample Collection
Fish were collected using a 9.144-m bag beach seine with 8 mm mesh. The
seine was utilized in a box-like pattern (Figure 4). Thirty (30) fish were sampled from
three (3) sites within twenty-four estuaries in New Brunswick, Nova Scotia, and
Prince Edward Island in the southern Gulf of St. Laurence (sGSL).
WATER
BEACH
Figure 4: Diagram illustrating bag beach seine sampling technique. Seine was
pulled into water following the basic pattern outlined above using the following
technique: (1) seine pulled into water from shore until the bag first enters the water,
(2) seine then pulled parallel to shore until end of seine is reached, (3) seine is pulled
back into shore to complete the box-like pattern, and (4) both sides of the seine are
pulled onto the shore simultaneously (at a steady pace) trapping the fish in the bag
of the seine.
27
Fish from the seine were emptied into a container with water, sorted and
enumerated. The first thirty G. aculeatus were placed in individual 20mL vials with
10% formalin. Individual vials were used to prevent cross contamination of
ectoparasites between fish.
Each vial was labelled with the site, date and fish
number. The trachurus or marine form of G. aculeatus were identified based on
three main external features (Wootton, 1976): (a) a set of three relatively large
spines (compared to other stickleback species) that are found in a strait dorsal row;
(b) a full complement of scutes (bony plates) along the sides of the fish from the gill
area to the caudal peduncle, and (c) the presence of a keel on the caudal peduncle.
3.3 Dissections and preservation
In the laboratory each fish was transferred from 10% formalin to 70% ethanol
(EtOH) for at least 24 h. The gills, stomach and intestines of the fish were
thenremoved and preserved in individual labelled 7mL vials with 70% EtOH.
The gills were further dissected in a petri dish filled with 70% EtOH. Each gill
arch was removed (Figure 5a), and the filaments were dissected from each arch
(Figure 5b). The suspension of gill filaments was then examined under high power
(32x) for ectoparasites belonging to the Phylum Monognena and the Class
Copepoda using a Wild Makroskop tri-ocular dissecting microscope. Parasites were
separated based on Phylum or Class and morphology, enumerated, and removed to
individual 4mL vials with 70% EtOH or mounted on a microscope slide.
All 30 fish from Kouchibouguac, Cocagne, Tatamagouche, Caribou, and PEI
National Park were initially processed. However, the target sample size of 30 was
28
not reached for all estuaries, and 10 fish were randomly selected from these
estuaries to be used in the data analysis. There was no difference between the
average parasites intensities of the subsample and the entire sample. For all other
sites, only 10 fish were dissected.
Gill Arch
CUT
CUT
(a)
Gill Arch
(b)
Gill Filaments
Figure 5: Gill dissection (a) gill arch removal, (b) gill filament removal.
The guts were removed from the 7mL vial and placed in a petri dish with 70%
EtOH. All organs attached to the gut area were removed and replaced in the 7mL
gut vial; the exterior of the gut was then examined for the presence of endoparasites
from the Phylum Nematoda. Parasites were recorded and the nematodes were
removed from the exterior of the gut and placed in a 7mL or 4mL vial filled with a
50:50 mixture of 70% EtOH and glycerol. The internal portions of the gut were
examined for any members of the Phylum Cestoidea after a shallow cut was made
along the length of the gut (Figure 6) using a pair of Lee Valley Tools Ltd. (Ottawa)
conjunctiva scissors. Cestodes were carefully removed with a probe or the section
of the gut they were attached to was dissected and placed in a vial with 70% EtOH
and a label. Only a single cestoide was found, and it was stained and mounted on a
microscope slide.
29
Stomach
Esophagus
Intestine
CUT
Gut
Figure 6: Diagram of fish gut dissection.
Finally the remainder of the gut contents was pushed into the petri dish using a
blunt probe and examined under medium (16-20x) and then high power (32x) using
the same dissecting microscope that was used for the gill dissections. The gut
contents were searched for any additional cestoides, as well as members of the
Phyla Digenea and Acanthocephala. Parasites were separated based on phylum
and morphology, enumerated and placed in individual vials with 70% EtOH and a
label. Food items were also identified and counted when possible.
3.4 Staining and Mounting
The method of staining and mounting depended on whether the parasite was an
ecto- or endoparasite as well as on its Phylum or Class. However, all specimens
were identified and photographed using the same microscope set-up, which
consisted of an Olympus CH Phase Contrast compound microscope with a tri-ocular
30
MTV-3 mount with 5x LD magnification. Attached to the tri-ocular mount was a
Pixera PVC100C Digital Microscope (Pixera Corporation, Los Gatos) camera.
Ectoparasites were not stained due to their extremely small size (Monogenea)
and the impermeability of the exoskeleton (Copepoda). They were mounted directly
from the sorting dish in a temporary mounting medium (Polyvinyl lactophenol; BDH
Gurr Microscopy Materials). This method, because of its clearing properties, causes
the eventual breakdown of the specimen due to the clearing properties of polyvinyl
lactophenol, each specimen was photographed to provide permanent evidence
(Figure 7). The monogeneans were identified using Beverley-Burton (1984), while
copepods were identified using Kabata (1988)
The endoparasites from Class Digenea and Cestoidea (Figure 8) were stained in
Borax-Carmine. Parasites are placed from 70% EtOH into a 4 mL vial containing
approximately 1 mL of stain for 5-30 min; the length of time spent in various stages
was dependant on the specimen’s size. Borax-Carmine is an over-stain; upon
removal from the stain, specimens were rinsed in 70% EtOH and then placed in a 4
mL vial with approximately 2 mL of acid alcohol for 24 h. Occasionally digenea were
counterstained with Malachite Green for 5-30 min. This counterstain was used to try
and differentiate the organs used to identify different species. Then specimens were
moved up the dehydration scale from 70-100% EtOH in 10% increments. Once the
specimen reached 100% EtOH, for at least 30 min, it was transferred to a glass 7 mL
vial with approximately 5 mL of Xylene (Fisher Scientific, Halifax, NS) for 5-30 min in
order to clear the specimen. Once cleared the specimen was permanently mounted
in Canada Balsam.
31
Figure 7: Monogenean specimen mounted in polyvinyl lactophenol, illustrating the clearing properties of the medium.
32
(a)
(b)
Figure 8: Digenean specimens stained and mounted using (a) Borax-Carmine alone, and (b) Borax-Carmine counterstained
with Malachite green.Both digeneans and cestoides were identified with the key by Hoffman (1999). Three additional keys
were also used for the identification of digeneans; Schell (1985), Gibson (1996), and Schell (1970). Tapeworms were
identified using Schmidt (1970).
33
3.5 Parasite identification
The following keys were utilized in the identification of the various types of
parasites discovered through the progression of this project (Table 5).
Table 5: Keys used for identification of parasites.
Group
All Phyla
Monogenea
Copepoda
Acanthocephala
Digenea
Digenea and
Monogenea
Digenea and
Monogenea
Cestoidea
Key
Hoffman (1999)
Beverly-Burton
(1984)
Kabata (1988)
Arai (1989)
Gibson (1996)
Schell (1985)
Schell (1970)
Schmidt (1970)
3.6 Statistical analyses
The data matricies of infracommunity endoparasites were examined using
detrended Correspondence Analysis (DCA) (PC-ORD v4.0; McCune and Mefford
1999) to determine the relationship among estuaries as well as among parasites.
Parasite infra- and metacommunity ectoparasite data and metacommunity
endoparasite data were explored using of PRIMER 5 (Clarke & Warwick 2001). The
data set was not transformed and the similarities were calculated using the BrayCurtis coefficient between every pair of samples (individual fish or estuaries). The
34
similarity matrix was then used to plot a cluster dendogram, with the cluster mode
being group average. The similarity matrix was also used to create a non-Metric
Multidimensional Scaling (nMDS) plot, which was created using at least thirty
restarts.
The cluster dendogram was compared to the raw data to determine how the
break points of the plot aligned with the original data. Lines of similarity were drawn
on the plot at three different levels of similarity, to delineate zones of similarity on the
nMDS plot. Salinity, water temperature and date of sample collection were also
plotted on the nMDS plots to see if the pattern present was correlated to these
factors.
35
Chapter 4
Results
4.1 Biodiversity
The results for ectoparasites and endoparasites are presented and analyzed
separately.
4.1.2
Ectoparasites
4.1.2.1 Descriptive results
Four types of ectoparasites were collected from the southern Gulf of St. Lawrence
(sGSL); three species were arthropods and one was a platyhelminth (Table 6).
4.1.2.2 Gyrodactylus spp.
Gyrodactylus sp. is a member of the order Gyrodactylida Family Gyrodactylidae
(Figure 9 & 10a) those that were collected were small and cylindrical. They have two
cephalic lobes and no eye-spots (Figure 10b). Marginal hooks are evenly distributed
on the opisthaptor with two hamuli present (Figure 10c). Larvae were visible in the
uteri of all specimens collected (Figure 9). Gyrodactylus sp. are parasites of
freshwater, brackish and marine teleosts. They have a direct life cycle and are
viviparous (Beverley-Burton 1984).
Gyrodactylus spp. were collected from every estuary (Table 7), with an overall
prevalence of 35.4% (39 of the 110 fish collected). The highest prevalence of
36
Table 6: Taxonomic designations of ectoparasite types collected in the sGSL.
Phylum
Platyhelminthes
Arthropoda
Arthropoda
Arthropoda
Unknown
Class
Monogenea
Crustacea
Crustacea
Crustacea
Subclass
Monopisthocotylea
Entomostraca
Entomostraca
Branchiura
Order
Gyrodactylida
Copepoda
Copepoda
none
Family
Gyrodactylidae
Ergasilidae
Ergasilidae
none
Genus
Gyrodactylus
Thersitina
Ergasilus
Argulus
Cysts
37
(a)
(b)
(c)
(d)
Figure 9: Composite image of the different types of Gyrodactylus collected from Cardigan River, PEI (a) Cg1-010731-006Ga-L-Mg1-26, (b) Cg1-010731-008-Ga-L-Mg1-27, (c) Cg1-010731-015-Ga-L-Mg1-29 and (d) Cg1-010731-015-Ga-L-Mg131.
38
cephalic
lobes
larvae
(b)
(a)
marginal
hooks
hamuli
(c)
Figure 10: Plate illustrating features of Gyrodactylus sp. (a) Cg1-010731-006-Ga-L-Mg1-26 (circle outlines uterus containing
larvae), (b) anterior of worm with the two cephalic lobes, and (c) opisthaptor at the posterior of the worm with marginal hooks
and both hamuli visible.
39
Table 7: Abundance of each parasite species in each estuary with the total number of each parasite species collected from
the sGSL, the total number of parasites collected per estuary, the number of different parasites found at each site and the
number of fish sampled per site.
Parasite Type
K
R
Co
BV
RP
T
C
Mg
NP
Cg
M
Average
Gyrodactylus sp.
20
4
8
4
5
26
40
1
16
42
7
15.73
Thersitina
0
40
0
5
0
0
0
0
0
0
0
4.09
Ergasilus
42
0
2
0
0
0
0
29
24
0
0
8.82
Cysts - unknown
1
0
0
0
1
0
0
6
3
7
1
1.73
Argulus sp.
0
1
0
0
0
0
0
0
0
0
0
0.09
total # parasites
63
45
10
9
6
26
40
36
43
49
8
30.45
total # fish sampled
10
10
10
10
10
10
10
10
10
10
10
total # parasite sp per fish
3
3
2
2
2
1
1
3
3
2
2
0.73
40
Gyrodactylus was at Cardigan, PEI (42 animals on 5 fish, maximum intensity 23
individuals per fish, minimum 3 per fish) and Caribou, NS (40 specimens from 8 fish,
maximum 15 per fish, minimum 2). Relatively high infections were found at
Kouchibouguac ( maximum of 10 per fish), Tatamagouche (maximum 16 specimens
per fish) and PEI National Park (maximum 15 per fish). Six estuaries had a total of
<10 Gyrodactylus, and they were found on a single fish at Cocagne, (8 specimens),
River Philip (5) and Merrigomish (1) and low intensities a the other estuaries
(Richibucto,2 ; Baie Verte, 2; Murray Harbour, 3).
4.1.2.3 Copepoda
Ergasilus sp. (Figure 11a) is a member of the Family Ergasilidae. The longest
axis of the body is from the anterior to the posterior. The cephalothorax is slightly
flattened dorsoventrally (Figure 11a) and the second antennae are highly modified
for attachment to the host (Figure 11b). Ergasilus sp. are parasites of freshwater
and marine fishes only (Kabata 1988).
Ergasilus sp. were found on 19 of the 110 fish (17.2%), but were only located in
Kouchibouguac (42 specimens from 9 fish, maximum intensity 16 specimens per
fish), Merrigomish (29 specimens from 5 fish, maximum 15), PEI National Park (24
specimens from 5 fish, maximum 8) and Cocagne (2 specimens from 2 fish) (Table
7).
Thersitina gasterostei (Figure 12) is also a member of the Family Ergasilidae.
The cephalothorax is largely inflated with the longest axis being the dorsal-
41
modified
legs
egg sacs
(a)
(b)
modified
second
antennae
primary
antennae
(c)
(d)
Figure 11: Composite image of the copepod Ergasilus sp. (a) anterior region (9x), (b) posterior region (9x), (c) first antennae
and second antennae modified for attachment, and (d) close up of modified second antennae (45x).
42
dorsal bump in
cephalothorax
egg sac
(a) gill filament
modified
antennae
(b)
modified
legs
(c)
Figure 12: Composite image of the copepod Thersitina gasterostei. (a) whole mount, (b) antennae modified for attachment,
and (c) modified legs.
43
ventral one. There is a large bump on the dorsal surface, along with the modified
antennae. The second antennae were modified for attachment to the host. T.
gasterostei parasitize fresh water and brackish water populations of Gasterosteus
aculeatus, and Pungitius pungitius (Kabata 1988).
Theristina gasterostei was collected from 9 of the 110 fish (0.08%) (Table 7), but
were only located in Richibucto (40 specimens from 7 fish, maximum 9) and Baie
Verte (5 specimens from 3 fish, maximum 2).
As members of the Family Ergasilidae Ergasilus sp. and T. gasterostei have
similar direct lifecycles. Only the female is parasitic. Males of both genera are freeliving throughout their entire life cycle. Females mate during their free-living stage
before finding and settling on a host (Kabata 1988).
A single Argulus was also found on a specimen from Richibucto.
4.1.2 Endoparasites
Seventeen taxa of endoparasites (Table 8) were collected from the sites sampled
in the sGSL. Estuaries differed in the type of parasites and abundance of each
(Table 9). Digenea were the most abundant class of parasite, with 12 species
recovered. Only one cestode (Bothriocephalus sp.) and two acanthocephalans were
collected from all the fish sampled. Nematodes were also found but due to their
allogenic parasitic life-cycles, were not discussed further in this thesis.
44
Table 8: Taxonomic designations of endoparasite types collected in the sGSL. Abbreviations the first D represents
the Class Digenea, the second letter represents an arbitrary designation assigned during sorting to differentiate
between different species of digenea.
Phylum
Platyhelminthes
Platyhelminthes
Platyhelminthes
Platyhelminthes
Platyhelminthes
Platyhelminthes
Platyhelminthes
Platyhelminthes
Platyhelminthes
Platyhelminthes
Platyhelminthes
Platyhelminthes
Platyhelminthes
Acanthocephala
Nematoda
Class
Digenea
Digenea
Digenea
Digenea
Digenea
Digenea
Digenea
Digenea
Digenea
Digenea
Digenea
Digenea
Cestoidea
unknown
unknown
Family
Hemiurinae
Hemiurinae
Opecoelidae
Opecoelidae
Opecoelidae
Lissorchiidae
Lepocreadiidae
Lecithasteridae
unknown
unknown
unknown
unknown
Bothriocephalidae
Subfamily
Lecithochiriinae
Hemiurinae
none
unknown
unknown
unknown
none
Lecithasterinae
None
Genus
Brachyphallus
Hemiurus
Podocotyle
Species
crenatus
levenseni
angulata
Lepocreadium
sp
Bothriocephalus
Code
DA
DP
DQ
DB
DD
DC
DE
DF
DG
DJ
DK
DR
sp.
45
Table 9: Abundance of each parasite species from 10 fish in each estuary.
Parasite
DA
DB
DC
DD
DE
DF
DG
DJ
DK
DP
DQ
DR
Nematoda
Nematoda
cyst
total #
parasites
species per
site
Species
Brachyphalus
crenatus
Lepocreadium
sp.
Hemiuris
levinseni
Podocotyle
angulata
K
823
R
270
Co
176
BV
113
RP
0
T
704
C
1495
Mg
0
NP
223
Cg
227
M
134
Total
4165
12
0
0
0
19
0
0
0
6
0
0
27
0
14
0
0
0
0
15
0
0
0
2
0
0
0
0
0
0
0
8
0
11
0
0
0
2
0
0
0
0
0
26
0
50
14
51
27
0
0
0
0
0
3
0
0
0
0
0
0
0
0
0
0
0
0
0
137
0
0
0
0
294
1
0
0
0
0
0
0
20
0
0
0
0
0
0
155
2
0
0
0
0
0
0
0
8
0
0
0
0
0
12
6
0
20
8
598
0
0
0
0
0
0
0
1
0
0
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
1
0
81
1
0
0
1
0
0
3
3
0
0
2
81
7
5
835
292
209
264
310
707
1516
246
237
243
174
5033
2
3
3
3
3
3
3
5
4
5
4
46
Although there were 12 species of digeneans identified, the maximum number of
species per estuary was 4 (Merrigomish) and the minimum was 2 (Kouchibouguac).
They were found in every estuary, with a maximum at Caribou (1515 specimens)
and the fewest were found at Merrigomish (174) and Cocagne (Table 9). Of the 12
species found, only 4 could be identified. The remaining species were new records
or new species. In some cases the families could be identified (Digeneans DB-DF),
but for several species, there were no known matches. Each species is represented
individually.
4.1.2.1 Brachyphallus crenatus
The body of Brachyphallus crenatus has a cylindrical body and elongate
(length≈0.75mm, width≈0.214mm) (Figure 13a). The anterior three-quarters of the
ventral surface of the B. crenatus is covered in distinct transverse annular plications.
Near the anterior of the worm these plications occur closer together and appear to
be slightly crenulated (Figure 13b). The transverse annular plications of the dorsal
body surface are only visible in the anterior region from the oral sucker to posterior of
the ventral sucker. The size of B. crenatus varies depending on the position of the
escoma (Figure 13e), a protrudable area found at the posterior of the worm (Gibson
& Bray 1979). A main identifying characteristic of B. crenatus is the presence of a
presomatic pit (Figure 13c), located between the oral and ventral suckers. The oral
sucker (Figure 13c) is ventrally subterminal, i.e. located slightly below the anterior tip
of the worm. B. crenatus has no prepharynx, however there is a muscular pharynx
is present. The ventral sucker (Figure 13c) is located in the anterior third of the body
of B. crenatus and is slightly larger than the oral sucker.
47
(a)
(b)
transvers annular plications
escoma
oral
ventral
sucker sucker
(c)
presomatic pit
vitelline glands
testis
(e)
(d)
ovary
Figure 13: Composite image of Brachyphallus crenatus (stained in Borax-carmine) sampled from a G. aculeatus in PEI
National Park estuary (NP1-010814-001-Ga-G-DgA2). (a) whole mount of specimen (9x), (b) close up of transverse annular
plications (45x), (c) anterior focused on oral and ventral suckers and presomatic pit (15x), (d) mid-body with testes, ovaries
and eggs (15x), (e) posterior with withdrawn escoma (15x).
48
Brachyphallus crenatus has a single pair of testes (Figure 13c) that are located
just posterior of the ventral sucker, and are arranged obliquely to each other. The
ovary (Figure 13d) is located in the middle third of the body (including the escoma)
ventro-medially, but is slightly displaced by the uterus. The ovary is found
immediately anterior (or anterior-dorsal) to the vitelline masses. The vitellaria
(Figure 13d) occurred as two large lobed masses, the lobes are short and broad and
the masses are slightly larger in breadth than in length. There are usually four lobes
in one mass and three lobes in the other. The vitelline masses occur symmetrically
in the ventral fields immediately posterior to the ovary.
Brachyphallus was found in all estuaries except River Philip and Merrigomish, NS
(Table 9) and was present on a total of 82% of fish captured at other estuaries
(74/90). Prevalence was highest at Caribou (1495 specimens from 9 fish, with a
maximum intensity of 408 and a minimum of 3) and Kouchibouguac (823 specimens
from all 10 fish, maximum 253 and minimum 1). All other sites showed high rates of
infection, with all sites having more than 60% of fish infected, with maximum
infection rates ranging from 35 to 360 specimens per fish.
4.1.2.2 Digenean B
Digenean B (Figure 14a), Family Opecoelidae, has an oval to round shaped
body, with a length (≈**) approximately 1.5 times the size of the width (≈**) at the
largest point. The body shows no ornamentation. The oral sucker (Figure 14b) is
well developed, as is the pharynx and ventral sucker (Figure 14c), the latter is
located pre-equatorially.
49
vitellaria
(a)
(c)
ventral sucker
(b)
uterus
testis
oral
sucker
genital pore pharynx
ovary
(d)
Figure 14: Digenean ‘B’ (a) whole mount of specimen NP1-010814-012-Ga-G-DB (9x), (b) oral sucker (15x), (c) ventral
sucker (15x), and (d) testes and ovary (15x).
50
The testes (Figure 14d) are oblique and located near the midbody and the ovary
is irregularly shaped and is located submedially anterior to the testes. The vitelline
glands are follicular (Figure 14a) and located marginally. They extend from the
posterior end of the worm toward the anterior end but they do not extend past the
ventral sucker. The uterus (Figure 14a) winds around the midbody anterior to the
testes near the ovary, dorsally near the ventral sucker and ends sub-medianally near
the pharynx where the genital pore is located.
Digenean B was found in 5 estuaries (K, R, Co, NP, Cg), on a total of 38% of fish
(19/50) at those sites. The maximum intensity was 16 specimens per fish
(Richibucto), and 13/19 fish had 1 or 2 specimens.
4.1.2.3 Digenea C: Family Lissochiidae
Digenea C (Figure 15a) has an oval body, which at its greatest width (≈0.42mm)
is approximately half its length (≈0.9mm). The body surface, with the exception of
the posterior end, is covered in crenulated transverse annular plications (Figure
15b). The oral sucker (Figure 15c) is relatively small and is located at the anterior
(almost terminal) end of the worm. The ventral sucker is approximately 2 to 2.5
times as large as the oral sucker and is situated in the anterior third of the body.
The testes are round, located just posterior to the ventral sucker, opposite one
another and are partially surrounded by the uterus and eggs (Figure 15d). The ovary
is oval and located posterior to the testis but just anterior of the vitellarium gland.
The ovary’s position is marginal (Figure 15a & b) and this may in part be due to
displacement by the uterus. The vitellaria are compact, oval, un-lobed (Figure 15a
51
ovary
transverse
annular
plications
testis
vitelline
gland
(a)
(c)
uterus
ventral
sucker
(b)
oral
sucker
(d)
genital pore
Figure 15: Composite image of digenean ‘C’ (DC) (a) Whole mount (9x), (b) margin of worm showing transverse annular
plications (15x), (c) Anterior third of body focused on oral sucker and anterior half of ventral sucker (15x), (d) genital pore of
uterus (15x). The specimen was tentatively identified as a member of the family Lissochiidae.
52
& Figure 15 b), and located marginally in the anterior half of the body just posterior to
the ovary. The uterus is located in the mid-body, but does not extend into the
posterior or past the ventral sucker (Figure 15a). The genital pore of the uterus
appears to be located near the lip of the ventral sucker (Figure 15d). The eggs are
relatively large and do not appear to be embryonate or operculated.
This species was only found at Baie Verte, with a total of 14 specimens coming
from 5 fish, with a maximum intensity of 5 specimens per fish.
4.1.2.4 Digenean D: Family Opecolidae
Digenean D (DD), Family Opecoelidae, has an oval body (Figure 16a) with and
approximate length of 0.9mm and width of 0.42mm. Its tegument is unarmed but
slightly crenulated. The oral sucker (Figure 16b) is muscular and located at the
anterior end of the worm. The ventral sucker (Figure 16c) is muscular, larger than
the oral sucker and embedded.
Digenean D has two testes (Figure 16d) lying in tandem or slightly oblique to
each other subequatorially near the posterior of the body. The ovary (Figure 17d) is
round and located in the median or submedian area of the body, anterior to the
testes.
The vitellaria (Figure 16a) are follicular and extend from the posterior of
digenean D slightly into the forebody. The uterus (Figure 16 a & c) extends between
the gonads and ventral sucker and, in the specimen examined for this study,
contains numerous large operculated eggs. The excretory pore is I-shaped (Figure
16e) and located at the posterior end of digenean D.
53
oral sucker
ovary
vitillaria
ventral
sucker
(a)
egg
uterus
(b)
(e)
excretory
pore
crenulate tegument
testis
(c)
(d)
Figure 16: Composite images of digenean ‘D’ (Tentative identification as Family Opecoelidae) focusing on important features
(a) whole mount of specimen NP3-010814-003-Ga-G-DgD (9x), (b) oral sucker (15x), (c) ventral sucker and uterus
containing eggs (15x), (d) testes and ovaries (15x), and (e) excretory vesicle (15x).
54
This species was found in four estuaries (RP. T, Mg and M), but was relatively
rare. It was found on 32% (13/40) of fish in those estuaries, with a maximum of 24
specimens on one fish at Murray Harbour. There were two or less specimens in
10/13 infected individuals.
4.1.2.5 Digenean E: Lepocreadium setiferoides
Lepocreadium setiferoides (Figure 17a) has a round, slightly oval, dorsoventrally
flattened body with a small indent at the posterior end (length≈0.643mm,
width≈0.562mm). The tegument of L. setiferoides is covered in small spines (Figure
17b). The oral sucker is large and muscular and located at the anterior end. The
ventral sucker (Figure 17c) is simple and smaller than the oral sucker. It is located
near the median of the worm, anterior to the egg masses.
There are two testes (Figure 17d) oriented opposite to each other, and located
sub-equatorially near the posterior end. The ovary is round and located anterior to
the testes but posterior to the egg mass. The vitellaria are follicular and extend from
the hindbody into the forebody, but not past the oral sucker. The uterus (Figure 17d)
is pretesticular and, in the specimens examined for this study, contained a few large
eggs along the equatorial line of the worm.
This species was seen only in four fish at Cocagne, with the maximum being 11
specimens.
55
oral
sucker
spine
(b)
(a)
(c)
oral
sucker
vitellaria
eggs in
uterus
ovary
testis
(d)
Figure 17: Composite picture of Lepocreadium setiferoides sp. (DE) (a) whole mount of specimen Co7-010718-013-Ga-GDgE5, (b) spines on margin of worm, (c) small ventral sucker posterior to oral sucker, (d) eggs, ovary, testes and vitelline
glands.
56
4.1.2.6 Digenean F
The body of Digenea F, possibly a member of Subfamily Lecithasterinae, is round
to oval or almost pear-shaped with a non-spinous tegument (length≈**, width≈**)
(Figure 18). The oral sucker is small and muscular, and there is a muscular
esophagus and a pharynx is present. The ventral sucker is muscular and large,
approximately three times the size of the oral sucker. It occupies about1/3rd of the
worm body as seen in Figure 18a the testes, ovary and vitellaria are obscured by the
uterus, eggs and ventral sucker, which prevented conclusive species identification.
Digenean F was only seen in three estuaries (R, T and NP) in a total of 4 fish and
maximum intensity of 2 specimens in one fish.
4.1.2.7 Digenean G
Digenean G is a rather unusual shape for a digenean, being oval to egg-shaped
with a sac containing organs bulging near the ventral sucker (Figure 19). Upon close
examination, both the oral and ventral sucker are visible, however, other than the
unknown organ in the sac there are no other organs visible. This leads to two
possible conclusions about this species: (1) this is a new unnamed species with a
very unusual body plan where in all the reproductive organs are grouped in the saclike organ located near the ventral sucker, or (2) this is a larval specimen that has
not completed development and is therefore unidentifiable.
Only one specimen of Digenean G was seen, in a single fish from Cocagne. The
fish was not selected in the random sampling for the inter-estuary comparison.
57
obscured area containing:
testis, ovary, vitellaria
eggs in the uterus
ventral
sucker
oral
sucker
Figure 18: Major features of digenean ‘F’ (possible Subfamily Lecithasterinae) (a)
whole mount Co7-010718-023-Ga-G-DgF1, (b) oral and ventral suckers, (c) testes,
ovary and vitellarium, and (d) eggs.
58
oral sucker
organ
sac
ventral
sucker
(a)
(b)
(c)
Figure 19: Composite plate of digenean ‘G’ (Co7-010714-029-Ga-G-DgG1) (a) whole mount (9x), (b) close up of ventral and
oral suckers (15x), and (c) close up of sac containing undetermined organs located near ventral sucker (45x).
59
4.1.2.8 Digenean J:
Digenean J (Figure 20a & b) has an oval, dorsoventrally flattened body, with was
non-spinous tegument. The oral sucker is muscular and well developed (Figure
20c), and approximately ¼ the size of the ventral sucker. The ventral sucker is
large, oval-shaped, spans the width of the body and located in the anterior region of
the body (Figure 20b).
Although there was an organ mass present it was impossible to discern the
individual organs, thus rendering identification of digenean J impossible.
This species was also only seen at Caribou, and was seen in two fish, with 16
specimens being the highest.
4.1.2.9 Digenean K:
Digenean K (Figure 21) is an oval to egg-shaped digenean with a non-spinous
tegument that is non-spinous. Both the oral and ventral suckers are visible and
muscular. The ventral sucker is located in the midbody.
Organs were visible in the hindbody, however it was impossible to distinguish
them well enough to permit a possible identification.
This species was only found in two fish at Cardigan, with 3 and 5 specimens.
60
ventral sucker
oral sucker
(c)
(a)
organ mass (b)
Figure 20: Composite plate of digenean ‘J’ (C3-010726-009-Ga-G-DgJ1) (a) whole mount specimen (9x), (b) close up of
anterior region showing large ventral sucker (15x), and (c) close up of muscular oral sucker (45x).
61
oral sucker
ventral
sucker
organ
mass
(b)
(a)
(c)
Figure 21: Composite picture of the various forms of digenean ‘K’, (a) Cg1-010731-015-Ga-G-DgK1 (9x), (b) Cg1-010731015-Ga-G-DgK2 (9x) and (c) Cg1-010731-015-Ga-G-DgK3 (9x).
62
4.1.2.10 Hemiurus levinseni
Hemiurus levinseni (Figure 22a) has an elongate and cylindrical body and like B.
crenatus it has an escoma, but no presomatic pit. Its escoma is short and extends to
about ¼ the body length. Dorsally and laterally the tegument is covered with annular
plications (Figure 22b), which smooth out towards the posterior end of the main
body. There are no plications on the escoma. Ventrally, the annular plications
extend from the anterior to the testes and then fade posteriorly.
The oral sucker (Figure 22c) is ventrally subterminal and surmounted by small
pre-oral lobes. There is no pre-pharynx but an oval muscular pharynx is present.
The ventral sucker (Figure 22c) is approximately the same size as the oral sucker
and is located in the anterior half of the worm.
There are two relatively large oval testes (Figure 22d) positioned obliquely to
each other. They are located posterior to the ventral sucker in the middle of the
body and are partially obscured by the uterus in Figure 22d. The ovary is globular
and located near the middle of the hindbody (not including the escoma). The
vitellaria are not lobed (unlike those of B. crenatus), orientated slightly obliquely to
each other and are located immediately posterior to the ovary. The uterus (Figure
22d) rarely extends posterior of the ovary, instead it loops around the midbody
partially obscuring the testes and ovary. The uterus joins the base of the sinus sac
near the margin of the ventral sucker. The eggs are small, numerous and
operculated. The sinus sac is tubular and passes ventrally into the anterior end of
the worm where it emerges near the pharynx (Figure 22e).
63
annular
plications
(a)
oral sucker
ventral
sucker
gonadopore
sinus
sac
uterus
(b)
(e)
vitellaria
(c)
(d)
testis
ovary
Figure 22: Picture of Hemiurus levinseni (DP) (a) whole mount of specimen RP2-010912-002-Ga-G-DgP3 (9x), (b) annular
plications (45x), (c) oral sucker and ventral sucker (15x), (d) testes, ovary, vitellaria, uterus and eggs (15x), (e) gonadopore
and sinus sac (15x).
64
This species was found in four estuaries (BV, RP, Mg and M), in 62.5% (25/40) of
the fish sampled. The maximum ranged between sites from 6 to 207 specimens per
fish, with 14/25 infected fish having six or less digeneans per fish.
4.1.2.11 Podocotyle angulata (syn. P. staffordi)
Podocotyle angulata (DQ) has an oval body (Figure 23a), slightly cylindrical,
elongate and non-spiny tegument (Figure 23b). The well-developed oral sucker is
located near the terminal anterior end of the worm and is small in comparison with
the ventral sucker. The pharynx is also well developed. The ventral sucker (Figure
23c) is large and muscular and located in the anterior half of the body.
The testes (Figure 23a) are tandem and located near the posterior end of the
body. While the ovary (Figure 23a), which is irregular in shape and located anterior
to the testes. The vitelline glands are follicular and found along the margins of the
body extending from the ventral sucker to the hind body. The uterus winds in front of
the ovary towards the anterior of the worm and the gonadopore (Figure 23d), and
located left of the median near the esophagus, just below the pharynx.
This parasite was only found as a single specimen in one fish at Merrigonish.
65
uterus
vitellaria
oral
sucker
egg
(a)
testis ovary
pharynx
(b)
ventral
sucker
(c)
gonadopore
(d)
Figure 23: Composite picture of Podocotyle angulata (syn. P. staffordi) (DQ) (a)
whole mount of M4-010830-002-Ga-G-DgQ showing orientation of testes and ovary
(4x), (b) close up of tegument (10x), (c) close up of ventral sucker (10x), and (d)
position of gonadopore (in box) (10x).
66
4.1.2.12 Digenean R:
Digenean R did not match any features in the taxonomic keys used for this study.
The body (Figures 24 & 25) is oval near the anterior, where the suckers are located,
and cylindrical in the posterior half where the organs were located. The body has a
smooth non-spinous tegument. The oral sucker is located terminally and was
approximately ¾ the size of the ventral sucker. The ventral sucker is located in the
anterior half of the body; it is large and approximately spanned the width of the
anterior of the body.
The testes and ovary of these specimens are indistinguishable. The vitellaria
(Figure 24c) are glandular, oval and located marginally in the posterior region of the
body. The uterus wound around the mid-body between the ventral sucker and the
organ mass at the posterior.
The eggs are relatively large and few (Figure 25a).
The gonadopore is located ventrally, slightly anterior to the ventral sucker (Figure
25b). A unique feature of this parasite is the presence of an unusual gland-like
structure near the left margin of all the worms (Figure 25c).
This parasite was also only found at Merrigomish, in two fish, with intensities of
45 and 25 per fish.
67
ventral
sucker
(b)
(a)
oral
sucker
vitellaria
(c)
Figure 24: Digenean ‘R' (a, b) illustrating the variety in body plan shapes, and (c) vitelline gland (outlined in grey).
68
oral sucker
ventral
sucker
(a)
eggs
unknown
feature
gonadopore
(b)
(c)
Figure 25: Composite picture plate of digenean ‘R' (DR) (Mg3-010821-002-Ga-G-DgR2-2) (a) whole mount of specimen, (b)
possibly the gonadopore (in box) and (c) odd shaped unknown feature found in all specimens (in oval).
69
4.2 Community Ecology
4.2.1 Ectoparasites
Although there were probably multiple species of Gyrodactylus present, they were
treated as a single group. They are present at all sites, and with respect to analysis
of the data the main breakage points in the similarity matrices in the following
sections can be attributed to the total numbers of parasites rather than the species of
Gyrodactylus.
4.2.1.1 Metacommunity analysis
Similarly, the ectoparasite metacommunity was analyzed by creating a similarity
matrix for the estuaries and used to create a Cluster dendogram (Figures 26)
illustrating the groupings of estuaries. Based on the ectoparasite metacommunity
total abundance similarity matrix, the estuaries Caribou and Cardigan are the most
similar of all the estuaries (89.888%). This is because they both have more than 40
Monogenea recorded in them. The difference between these estuaries is that cysts
were collected from Cardigan but not from Caribou. River Phillip and Murray
Harbour (85.714%) are the second most similar estuaries. Cysts were collected
from both of these estuaries however they are different due to the number of
Monogenea collected, 5 Monogenea were collected from River Phillip while 7
Monogenea were collected from Murray Harbour. Kouchibouguac National Park and
PEI National Park were 77.358% similar based on their ectoparasites. Both
estuaries contained Ergasilus sp. (Cp2).
70
0
>40
Tg
Erg
< 20
Erg
> 20
Arg
60
Estuaries
ONLY
1
Gyro
NP
Gyro
< 40
K
M
RP
Co
BV
100
R
Erg
present
Gyro
≥ 40
Mg
80
15-20 Gyro
Cg
Cysts
present
C
Tg
present
T
% Similarity
40
Total ectos > 25
Total ectos ≤ 10
20
Figure 26: Cluster analysis dendogram illustrating the groupings of estuaries based on the ectoparasite metacommunity total
abundance similarity matrix with the criteria for each divergence plotted on the dendogram. Long dash (30%), Dot-long dash
(60%), and squares (80%) lines indicate levels of similarity. Abbreviations: Arg = Argulus sp., Tg = Thersitina gasterostei,
Erg = Ergasilus sp., Gyro = Gyrodactylus sp. and ectos = ectoparasites. The estuary abbreviations are the same as those
appearing in Table 10.
71
Through the analysis of the Cluster dendogram and the nMDS (Figure 27), two
major groupings of the estuaries were apparent: Tatamagouche, Caribou, Cardigan,
PEI National Park, Kouchibouguac National Park, and Merrigomish in one group and
Baie Verte, Murray Harbour, River Phillip, and Cocagne in another group with
Richibucto as an outlier. This division occurs based on the numbers of Monogenea
collected from each estuary. The Tatamagouche group having greater than 10
Monogenea collected per estuary, and the Baie Verte group having less than 10
Monogenea collected per estuary. The nMDS plot had a stress of 0.08 indicating
that there was very little chance of an error in the arrangement of the estuaries on
the plot.
The similarity matrix (Table 11) for the ectoparasite metacommunity
presence/absence data was used to create the cluster dendogram of the eleven
estuaries sampled. A cluster dendogram (Figure 28) was created using the similarity
matrix, it was then compared back to the original data to determine to potential
reason for the various breaking points. There were three groupings of estuaries
where the estuaries involved were 100% similar, that is the parasites present in each
estuary involved in the grouping were the same. The first group was Tatamagouche
and Caribou based on the presence of only one type of parasite, Gyrodactylus sp..
The second group that was 100% similar was Murray Harbour, River Phillip and
Cardigan based on the presence of only Gyrodactylus sp. and cysts. The third
grouping at 100% similarity consisted of Kouchibouguac National Park, PEI National
Park and Merrigomish. The estuaries Richibucto and Baie Verte and the next
72
Stress: 0.08
C
Cg
T
R
K
NP
Co
BV
M
Mg
RP
Figure 27: Non-metric Multidimensional Scaling (nMDS) plot of the groupings of estuaries based on the ectoparasite
metacommunity total abundance similarity matrix. K=Kouchibouguac National Park, R=Richibucto, Co=Cocagne, BV=Baie
Verte, RP=River Phillip, T=Tatamagouche, C=Caribou, Mg=Merrigomish, NP=PEI National Park, Cg=Cardigan, and
M=Murray Harbour.
73
Table 10 Similarity matrix of the ectoparasite metacommunity presence/absence data.
K
K
R
Co
BV
RP
T
C
Mg
NP
Cg
M
33.333
80.000
40.000
80.000
50.000
50.000
100.000
100.000
80.000
80.000
R
40.000
80.000
40.000
50.000
50.000
33.333
33.333
40.000
40.000
Co
50.000
50.000
66.667
66.667
80.000
80.000
50.000
50.000
BV
50.000
66.667
66.667
40.000
40.000
50.000
50.000
RP
66.667
66.667
80.000
80.000
100.000
100.000
T
100.000
50.000
50.000
66.667
66.667
C
50.000
50.000
66.667
66.667
Mg
100.000
80.000
80.000
NP
80.000
80.000
Cg
M
100.000
74
40
Tg
NO Tg
NO
Cysts
Mg
K
Cysts
NP
Cg
M
C
T
BV
R
100
ONLY
Gyros
RP
Gyros
&
Cysts
80
NO
Cysts Cysts
Gyros & Erg
Co
% Similarity
60
Estuaries
Figure 28: Cluster analysis dendogram illustrating the groupings of estuaries based on the presence/absence similarity
matrix with criteria for each divergence plotted on the dendogram. Long dash (50%), Dot-Long dash (70%), and squares
(90%) lines indicate levels of similarity. Abbreviations Tg – Thersitina gasterostei, Erg – Ergasilus sp., Gyro – Gyrodactylus
sp..
75
Stress: 0
Co
T
C
BV
K
Mg
NP
M
RP
Cg
R
Figure 29: Non-metric Multidimensional Scaling (nMDS) plot of the groupings of estuaries based on the ectoparasite
metacommunity presence/absence similarity matrix.
76
closely related estuaries with a similarity of 80%. The presence/absence cluster and
nMDS (Figure 29) indicated a major breakage in the similarity of the different
estuaries based on the presence, and subsequent absence, of Thersitina
gasterostei. The nMDS of the presence/absence data’s similarity matrix was 0
indicating that the orientation of the estuaries in the plot was “perfect”, and therefore
the best possible fit of the data in the plot
4.2.1.2 Infracommunity
The similarity matrix of ectoparasite infracommunity data was used to create a
Cluster Dendogram (Figure 30) illustrating the groupings of individual fish from the
different estuaries. Seven distinct major groupings can be distinguished from the
Cluster dendogram (Figure 30, Table 12).
The nMDS (Figure 31) had a stress=0.04 indicating high confidence in the plot.
The lines of similarity from the cluster dendogram were drawn onto the nMDS. At
the 40% similarity level individual fish from the same estuary are generally grouped
together, with a few exceptions though. Group one contained PEI National Park
(NP), River Phillip (RP) and Kouchibouguac National Park (K) fish. Group two
contained Richibucto (R) and Baie Verte (BV) fish, while group three contained
Merrigomish (Mg), PEI National Park (NP), Kouchibouguac National Park (K) and
two Cocagne (Co) fish. Group four mostly contains Cocagne (Co), Tatamagouche
(T), Murray Harbour (M), Caribou (C), as well as a few, Baie Verte (BV), PEI National
Park (NP), Cardigan (Cg), Kouchibouguac National Park (K) and River Phillip (RP)
fish.
77
0
% Similarity
20
40
60
100
K4
NP6
NP7
NP9
RP10
R4
BV6
BV2
BV5
R3
R7
R8
R2
R6
R9
Mg8
Co10
Mg1
K10
Mg2
NP2
K9
Mg7
Mg6
Co4
NP4
K3
Mg9
K1
NP3
K2
NP1
K5
K7
NP10
C9
Cg5
Co2
Cg10
Cg7
C7
C2
T6
M3
T1
T2
T3
BV8
BV10
M2
Co6
C5
C8
R1
M1
Co7
Co8
Co9
C6
Cg9
T10
Cg1
RP6
Co3
C1
T4
K6
Co1
80
G1
G2
G3
G4
G5
G6
G7
Figure 30: Cluster analysis dendogram illustrating the groupings of individual fish from the different estuaries based on the
ectoparasite infracommunity similarity matrix. Three levels of similarity are also plotted on the dendogram95%=small
squares, 70%=long dash and dot, 40%=long dash. G1 through seven outline major groupings of fish based on the types of
parasites present (Table 12).
78
Table 11:Table explaining the assignment of fish groupings in the ectoparasite infracommunity dendogram (Figure 31).
Fish
Main grouping criteria
groupings
G1 Group 1
Only Cysts present
Theristina gasterostei present,
G2 Group 2
either Tg = 9 or Tg < 4
#
Minor grouping criteria
Argulus sp. present in R4
Gyrodactylus spp. BV6 =
1, R2 = 2
G3 Group 3
Only Ergasilus sp. < 5 individuals Specific # of Ergasilus sp.
G4 Group 4
Gyrodactylus and Ergasilus sp.
1 Gyrodactylus spp. and
G5 Group 5
Ergasilus sp. >5 individuals
G6 Group 6
Gyrodactylus spp.>6 individuals
G7 Group 7
only Gyrodactylus spp.
Ergasilus sp. >15 and
Ergasilus sp. 4-6
Ergasilus sp. 2-3 with
Gyrodactylus spp. <16 or
only Gyrodactylus spp.
specific # of Gyrodactylus
spp.
79
Stress: 0.04
NP9
NP7
NP6
RP10
K4
M3
BV8
T3
T2
T1
R1
BV10
M2
C5
C8
Co6
Mg1
Co10
Mg8
Mg2
K10
NP2
K9
Mg7
K1
NP3
K2
NP1
Co4
NP4
Mg6
K5
K7
NP10
T10
Cg9
M1
C6
Co9
Co8
Co7
T4
K6
Co1
Co3
C1
Cg1
RP6
Cg5
C9
Co2
Cg10
C7
C2
T6
Cg7
BV6
BV5
BV2
R3
R8 R7
R2
R6
R9
R4
Mg9
K3
Figure 31: Non-metric Multidimensional Scaling (nMDS) plot of the ectoparasite infracommunity analysis with three similarity
levels 95%=small squares, 70%=long dash and dot, 40%=long dash used to delineate the groupings of the estuaries.
80
4.2.2 Endoparasites
4.2.2.1 Metacommunity Community
The endoparasite metacommunity total abundance data set was used to create a
similarity matrix of the estuaries from a cluster dendogram (Figure 32) and nMDS
plot (Figure 33) are created to illustrate the groupings of the different estuaries. The
cluster dendogram shows that the estuaries containing sticklebacks with the most
similar parasite metacommunitites are PEI National Park and Cardigan (94.167%).
Both estuaries had approximately 230 Brachyphallus crenatus (DA) (Average
abundance of B. crenatus =22 in PEI National Park, and Average abundance of B.
crenatus =22.7 in Cardigan), but differed with respect to PEI National Park having
DF and Cardigan having DK and nematode cysts. The next most closely related
sites are Kouchibouguac National Park and Tatamagouche (91.310%) which both
have 300-999 B. crenatus. Sticklebacks from Kouchibouguac National Park differed
from those collected from Tatamagouche by hosting DB, while fish from
Tatamagouche contained Lepocreadium setiferoides (DE), DF and nematodes.
The cluster analysis (Figure 32) and nMDS plot (Figure 33) both illustrate the
same division of the estuaries between one group containing Caribou,
Kouchibouguac National Park, Tatamagouche, Murray Harbour, Cocagne,
Richibucto, PEI National Park and Cardigan, and another group containing River
Phillip, Merrigomish and Baie Verte. This division occurs due to the presence of
Hemiurus levinseni (DP) in River Phillip, Merrigomish and Baie Verte, but its
absence in the rest of the estuaries.
81
0
>100 DP
<15 DP
<120DA
>120DA
>700 DA
N
No Nm
DB
Cg
DF DK, Nmcy
NP
C
Mg
100
RP
DE/F
>1000
DA
DJ
BV
DB
Co
DQ
DR
80
~230 DA &
Nm
<1000 DA
M
DA
&
DC
T
60
DP, >20DD, No
DB, Nmcy
No DA
R
40
K
% SIMILARITY
20
Figure 32: Cluster analysis dendogram illustrating the groupings of estuaries based on the endoparasite metacommunity
total abundance similarity matrix with the breakage points plotted on the dendogram. Abbreviations: DA=Brachyphallus
crenatus, DB=digenean ‘B’, DC=digenean ‘C’, DD=digenean ‘D’, DE=Lepocreadium setiferoides, DF=digenean ‘F’,
DJ=digenean ‘J’, DK=digenean ‘K’, DP=Hemiurus levinseni, Nm=Nematodes, Nmcy=Nematode cysts, K=Kouchibouguac
National Park, R=Richibucto, Co=Cocagne, BV=Baie Verte, RP=River Phillip, T=Tatamagouche, C=Caribou,
Mg=Merrigomish, NP=PEI National Park, Cg=Cardigan, and M=Murray Harbour.
82
Stress: 0.01
C
TK
RP
Mg
BV
R
Cg
NP
Co
M
Figure 33: Non-Metric Multidimensional Scaling (nMDS) Plot of the endoparasite metacommunity total abundance similarity
matrix information. K=Kouchibouguac National Park, R=Richibucto, Co=Cocagne, BV=Baie Verte, RP=River Phillip,
T=Tatamagouche, C=Caribou, Mg=Merrigomish, NP=PEI National Park, Cg=Cardigan, and M=Murray Harbour
83
The endoparasite metacommunity presence/absence data set was used to create
a similarity matrix. The cluster dendogram plot (Figure 34) and nMDS plot (Figure
35) generated illustrate the groupings of the different estuaries. The two estuaries
that were most similar were Richibucto and PEI National Park (85.714%) based on
the presence of DF, DA and DB, but not DK. They differed in sticklebacks from PEI
National Park had nematodes where those from Richibucto did not. The next closest
grouping was the endoparasite communities of fish from Kouchibouguac National
Park and Cocagne (80%), because they both contained DA and DB but not DK or
DF.
Overall, the estuaries were divided into two groups based on the presence or
absence of DP. Group one, which contained DP, consisted of Merrigomish, River
Phillip, Murray Harbour, Baie Verte and Tatamagouche (Tatamagouche being the
only estuary with no DP), while group two consisted of PEI National Park,
Richibucto, Kouchibouguac National Park, Cocagne, Cardigan and Caribou.
4.2.2.2 Infracommunity
The raw endoparasite infracommunity data were analysed by Detrended
Correspondence Analysis (DCA) using PC-ORD 4.0 (McCune & Mefford 1999). The
total inertia in the species data was 2.2626. The eigenvalue of the longest axis, Axis
1 was 0.907, while the second axis was 0.249 and the third was 0.134.
84
20
DP
40
DA, NO DP
% SIMILARITY
DA
DB
NO
DK
DP
60
NO
DA
DK
DF
DJ
Nm
NO
DB
NO
DF
DE
C
NO
DE
Cg
Nm
Co
BV
NO
Nm
K
M
DD
DF
NP
DC
R
DD
T
DD
RP
100
DQ
DR
Mg
80
Figure 34: Cluster analysis dendogram illustrating the groupings of estuaries based on the endoparasite metacommunity
presence/absence similarity matrix. Abbreviations: DA=Brachyphallus crenatus, DB=digenean ‘B’, DC=digenean ‘C’,
DD=digenean ‘D’, DE=Lepocreadium setiferoides, DF=digenean ‘F’, DJ=digenean ‘J’, DK=digenean ‘K’, DP=Hemiurus
levinseni, Nm=Nematodes, Nmcy=Nematode cysts, K=Kouchibouguac National Park, R=Richibucto, Co=Cocagne, BV=Baie
Verte, RP=River Phillip, T=Tatamagouche, C=Caribou, Mg=Merrigomish, NP=PEI National Park, Cg=Cardigan, and
M=Murray Harbour.
85
Stress: 0.09
C
Cg
NP
Mg
RP
K
Co
M
R
BV
T
Figure 35: Non-Metric Multidimensional Scaling (nMDS) Plot of the endoparasite metacommunity presence/absence
similarity matrix information.K=Kouchibouguac National Park, R=Richibucto, Co=Cocagne, BV=Baie Verte, RP=River Phillip,
T=Tatamagouche, C=Caribou, Mg=Merrigomish, NP=PEI National Park, Cg=Cardigan, and M=Murray Harbour.
86
The pattern created by the DCA (Figure 36, 37) was tongue shaped. Indicating
that the parasite data does not really fit the assumptions of used by the DCA model
of a continuum of normal distributions. This is probably due to this being an analysis
of the infracommunity level where in each individual fish is the ecosystem and it is
unlikely the comparison between individual host communities will create a
continuum. When the fish (samples) and the parasite (species) are plotted it is
evident that the main axis of variation is related to DE found in Co2 and Co3
One of the main causes for differences between fish was the presence DE
(Lepocreadium setiferoides) and DB. Lepocreadium setiferoides (DE) occurs in only
four hosts, and three of those four times it co-occurs with Brachyphallus crenatus
(DA), however in one instance it occurs with DB (2) in one host and in the absence
of B. crenatus (DA). This causes the plot to pull towards the left-hand-side.
A similar gradient occurs in this area between those fish containing high numbers
of DD (or Nm) in comparison to the number of Hemiurus levinseni (DP) found in the
same fish and those with high numbers of H. levinseni (DP) in relation to the number
of DD (or Nm). It is important to note that DD never co-occurs with Nm when H.
levinseni (DP) is also present. There is also a gradient present between fish in
which B. crenatus (DA), Nm and DD are present. These three parasites only cooccur in a single host M1.
It is worthy of note that DF and DK occurred only in fish where the sole other
parasite was B. crenatus (DA). Of the 94 hosts examined in the DCA 75 (79%) of
them contained B. crenatus (DA).
87
Axis 2
DD
RP3
M 10
Nm
CG2
MG8
M 1NP6
CG4
C
G9
T1
T4
M
4
D ECO 3 CO 2 D
R4BDF
CK
O
P9
K7
10
R1
CG
C
N
NP5
CO
NP8
NP4
CG7
CG10
K4
K3
K9
CG5
K1
K2
K6
K5
N
C8
C7
C5
C4
C3
C2
C1
C
K8
K10
C9
O
P10
O
G
P2
10
P7
39
7
9
1
6
R6
R3
R8
T3
T2
T10
T9
T7
T6
T5
R2
R5
R7
R
M
5148
D
A
DN
BV1
BV4
Axis 1
BV7
BV2
BV10
BV8
RP10
M
MG
G34
MG7
RP7
BV6 M G 5
M
G
1
R
P6
M
G
M
RP1
RP9
RP8
G
9
BV9
2 210
DP
Figure 36: Detrended Correspondence Analysis (DCA) plot of endoparasite infracommunity (e.g. Nm = Nematodes) and fish
hosts (e.g. BV7 = fish #7 from Baie Verte), with and envelope encompassing the individual fish hosts that contain that
specific parasite species. Lines illustrate the occurrences and overlapping of the different parasite species (Dot-long
dash=DA, Long dash=DD, solid=DE, squares=DP, and short dash=Nm). Parasite species abbreviations: DA =
Brachyphallus crenatus, DD = digenean ‘D’, DE = Lepocreadium (setiferoides) sp., DP = Hemiurus levinseni, Nm =
Nematodes.
88
Axis 2
DD
Contains:
RP3
DA;
Contains:
DB, DF, DK;
R4, NP9, Co10, R1
Co1,4,6,7, & 9; C1-5,
& 7-10; NP2, 4-8, &
10; Cg1, & 3-10; K110; M1, 3-5, & 9; T17, 9, & 10; R2-3, 5-8,
& 10; BV1 & 4
M 10
Contains:
Nm
DP;
BV9; M2; RP1, 6,
8, & 9; Mg1, 2, 5, 9
& 10
CG 2
M G8
M 1NP6
CG
G94
C
T1
T4
M
4
D EC O 3 C O 2 R4
D BD F
NP9
O
K7
10
R1
CG
C
NP10
NP5
C
N
NP4
CG
K4
K3
K9
K1
C
NP2
NP7
C8
C7
C5
C4
C3
C2
C1
K2
K6
K5
K8
K10
C9
O
O
P8
O
G
39
10
58
7
9
1
6
R6
R8
R3
R5
R7
R
T3
T2
T10
T9
T7
T6
T5
R2
10
M
5147
D
A
DC
K
BV1
BV4
Axis 1
BV7
BV2
BV10
BV8
RP10
M
MG
G34
M G7
RP7
BV6 M G 5
M
G
12
RP6
M
G
BV9
RP1
G9
G10
M
RP9
RP8
2
D
P
Figure 37: Detrended Correspondence Analysis (DCA) plot of endoparasite infracommunity (e.g. Nm = Nematodes) and fish
hosts (e.g. BV7 = fish #7 from Baie Verte), with and envelope encompassing the individual fish hosts that contain that
specific parasite species. Abbreviations DA = Brachyphallus crenatus, DB = digenean ‘B’, DD = digenean ‘D’, DE =
Lepocreadium (setiferoides) sp., DF = digenean ‘F’, DK = digenean ‘K’, DP = Hemiurus levinseni, Nm = Nematodes.
Outlined areas show contents of indicated areas of highly concentrated points.
89
Chapter 5
Discussion
DIVERSITAS is a program sponsored by the Secretariat of the Convention of
Biological Diversity, through UNEP (United Nations Environment Program;
http://www.biodiv.org/default.aspx). One of the many foci of the group is to
participate in a systematic inventory of world species and to foster the
organization of taxonomic databases (Loreau and Olivieri, 1999). The
stickleback project focuses on studying closely-related stickleback species and
their parasite distribution on a regional scale, and sampling has been conducted
in parts of Western Canada, Western US, Russia, Iceland, Germany, the UK,
Norway and the Faroe Islands (Macogliese, 2002). The project aims to compare
parasite diversity to diversity of other taxa. The distribution and abundance of
individual species will be compared across sites and regions, and patterns of
parasite species abundances and diversity will be evaluated in terms of
environmental parameters and biogeographic theory to evaluate the roles of local
versus regional determinants (Marcogliese, 2002).
This thesis reports on the parasite fauna of three-spine stickleback within the
southern Gulf of St. Lawrence. Samples were collected from 11 estuaries within
the Maritime Provinces. The data will be entered into the broader inventory for
comparison.
90
5.1 Parasite fauna of the three-spine stickleback
There were few ectoparasites encountered. Gyrodactylus spp. were
encountered in all of the estuaries, but only four other species were encountered,
and these were not widely distributed or present in very high intensities. The
number of ectoparasites was surprising. It is unlikely that they were lost during
processing, as fish were sampled into individual vials in the field to preserve the
ectoparasite communities.
The endoparasites were dominated by digeneans, with various species
present in all of the estuaries. Surprisingly, very few other parasites were
encountered.
5.1.1 Ectoparasites
5.1.1.1 Monogenea
Gyrodactylus spp. were collected from every estuary with an overall
prevalence on 35.4% of the stickleback (39 of the 110 fish collected). They have
been commonly reported previously on three-spine stickleback, with reports of
more than six species occurring across Canada (Beverley-Burton, 1984). The
various Gyrodactylus spp. known to occur on G. aculeatus have been recorded
from the Atlantic and Pacific Oceans as well as NF, NS, NB, QC, ON and BC
(Hanek and Threlfall 1969, Beverley-Burton 1984, Cone and Wiles 1985a,
Hoffman 1999). It was not possible to identify them to species level for this
study.
91
These specimens are known to be Gyrodactylus spp. because larvae were
visible in utero of the adult worm, and the anchors (hamuli) of the larva could also
clearly be seen. Gyrodactylus spp. are the only know monogenean genus that
are viviparous and where larvae, including anchors, can been seen in utero
(Hoffman 1999). Gyrodactylus are viviparous, and do not require another host.
They were present in very low numbers in six of the estuaries, and the total
numbers were very low. Previous studies have found that Gyrodactylus spp. are
usually present at much higher prevalence and intensity than were encountered
here (Cone and Wiles, 1985).
There is not expected to be a seasonal cycle in the intensity of reproduction of
these monogeneans, but the reduced infections may be related to the movement
patterns of three-spine stickleback in the sGSL. The three-spine stickleback will
spend May and June in freshwater portions of the estuary, and spend most of the
summer in slat water (Peddle, 2001). In this study, the fish were collected
between July and September, and no correlation was seen between capture date
and parasite frequency, or with temperature or salinity.
5.1.1.2 Copepoda
There are 8 known copepod species known to be parasitic in North America
(Kabata, 1988). The copepods found on G. aculeatus in this study corresponded
to those reported in the literature, where both Thersitina gasterostei and
Ergasilus sp. have been recorded. Thersitina gasterostei has previously been
recorded from the Atlantic Ocean, NF, QC, and BC (Kabata 1988), and this study
92
reports two new locations for this species. The Thersitina collected from fish in
sGSL is considered to be T. gasterostei because there is only one species of this
morphologically distinct group (Kabata 1988). It was recorded in relatively high
numbers in Richibucto and in much lower frequencies in Baie Verte. They also
have a direct life cycle, and have been reported on other species of fish, but not
in the sGSL.
There are two Ergasilus spp. that have previously been recorded on G.
aculeatus from Canada: Ergasilus auritus (NF, BC and Pacific Ocean) and
Ergasilus turgidus (BC and Pacific Ocean). E. auritus is found in euryhaline
areas where as E. turgidus is found in marine and brackish waters (Hoffman
1999, Kabata 1988). Prior to this study no Ergasilus spp. had been recorded
from G. aculeatus in the sGSL. They were found in four estuaries, and were seen
in all three Maritime provinces.
Ergasilus and Theristina were not found in the same estuaries, and Ergasilus
were present at sites with both high and low intensities of Gyrodactylus
infections. They co-occurred on two fish in Kouchibouguac (2 G, 6 E and, 1,3),
once in Cocagne (1 G, 3 E) and twice in PEI National Park (1,4 and 2, 15) , The
two sites with Theristina had low infections of Gyrodactylus, and they cooccurred at both sites in a single fish (9 T, 2 G in R; 1 and 1 in BV). Only a single
Argulus was found in Richibucto, and it co-occurred with one Theristina. The
specimen was found in the gill cavity, whereas Argulus are generally found on
the body wall (Kabata, 1988).
93
5.1.2 Endoparasites
Seventeen taxa of endoparasites were collected from the sites sampled in the
sGSL. Endoparasites were highly biased towards digeneans, and 12 species
were 12 species recovered. Only one cestode (Bothriocephalus sp.) and two
acanthocephalans were collected from all the fish sampled. Small numbers of
nematodes were encountered, and they were not studied. The nematodes are
allogenic, and their definitive host is higher in the food chain.
A study by Zander et al. (1999) showed a similar pattern, where digeneans
were the most commonly found type of parasite. That study also noted that
Gasterosteus aculeatus was the fish species that was host to the greatest
spectrum of parasites. (Zander et al. 1999).
5.1.2.1 Digenea
Although 12 species of digeneans were encountered, no estuary contained
more than four species, and six of the species were unique to a single estuary.
Unique species were found in all three provinces. Brachyphallus crenatus was
widely distributed, and was located in 9 of the 11 estuaries. The two estuaries
that did not contain B. crenatus had high infections with Hemiurus levinseni;
Hemiurus levinseni was co-located with B. crenatus in two estuaries.
5.1.2.1.1 Previous records in Gasterosteus aculeatus
Only three parasites collected from the G. aculeatus sampled in sGSL have
previously been recorded as parasites of this fish species. Those species are
94
Family Hemiurinae Subfamily Lecithochiriinae Genus Brachyphallus crenatus
(DA), Family Lecithasteridae Subfamily Lecithoasterinae (DF), and Family
Opecoelidae Genus Podocotyle angulata (DQ).
B. crenatus, is considered to be a parasite of marine teleosts (Gibson & Bray
1986). It has been recorded from: NF, NS, NB, PEI, Que, BC, NWT and YK in
Canada. The NF record was specifically from G. aculeatus (Hanek & Threlfall
1969), however even though one of the records for NB was not recorded as living
in G. aculeatus it was from the Northumberland Strait area (Frimeth 1987).
P. angulata is a parasite from the Family Opecoelidae, Subfamily
Plagioporinae that is most commonly found in brackish water, estuarine or
migratory fishes (Gibson & Bray 1986). It has been recorded from the Atlantic
Ocean, NB-b (brackish), NB and NF. However only the general Atlantic Ocean
record was a sample actually obtained from a G. aculeatus. The remaining
incidents of infection were recorded from its presence in other species of fish
(Gibson & Bray 1986). The records from NB and NB-b are from the sGSL,
specifically from Tabusintac River, NB that is just north of Kouchibouguac
National Park.
There is much debate in the identification of the specific species in the Genus
Podocotyle that are known to occur in G. aculeatus, especially between P.
angulata (=P. staffordi) and P. atomon. P. atomon is known as a parasite of
littoral and rock pool fishes and all the records of it from G. aculeatus are from
NF (Gibson 1996). P. angulata, on the other hand, has been recorded from G.
95
aculeatus only in the Atlantic Ocean (Gibson 1996); however it has been
recorded from the Northumberland Strait area on fish other than G. aculeatus
(Frimeth 1987). P. angulata is also known as a parasite which occurs in brackish
water, estuarine or migratory fish (Gibson 1996). It is likely that P. angulata
rather than P. atomon is the parasite found in the sGSL because it is an area that
has a primarily sandy/mud bottom.
DF was identified consistently to Family and Subfamily using several different
keys. Further identification, to Genus and subsequently Species was impossible
due to the lack of the visible identifiable features used to distinguish between the
two Genera found in the Subfamily Lecithasterinae: Lecithaster and
Lecithophyllum. However, DF probably belongs to the genus Lecithaster
because Lecithaster gibbosus is a known parasite of G. aculeatus (Gibson 1996).
L. gibbosus is an arctic-boreal species which infects marine teleosts and has
been recorded from G. aculeatus in NF (Hanek & Threlfall 1969, 1970) as well as
NS, NB, BC, and NT (Gibson 1996); the previous NB record is from the
Tabusintac River (Frimeth 1987).
5.1.2.1.1 New G. aculeatus records
The remaining eleven parasites collected are possibly new host records for G.
aculeatus and potentially new area records. From these eleven, only five could
be identified to Family and of those only two were identified to Genus and
species.
96
Hemiurus levinseni (DP) is a new host record as well as a new area record for
G. aculeatus in the sGSL. It is a member of the Family Hemiuridae, Subfamily
Hemiurinae and is a marine teleost parasite. H. levinseni has previously been
recorded from fishes in both the Atlantic and Pacific Oceans, the brackish waters
of BC, the Scotian shelf of NS, and NF (Gibson 1996, Arthur & Albert 1994,
Scott 1975, 1982, Sekhar & Threlfall 1970). Although H. levinseni has never
been recorded from G. aculeatus, it is not an unlikely infection because H.
levinseni is not very host-specific and has been recorded from a wide variety of
different host fish species (Gibson 1996). H. levinseni is known to occur on over
thirty different fish species in Canada including: Alosa sapidissima, Clupea
harengus, Mallotus villosus, Salmo salar, Urophycis chesteri (Gibson 1996). As
well H. levinseni is not the only member of the Family Hemiuridae known to infect
G. aculeatus; B. crenatus is a known parasite of G. aculeatus (Gibson 1996).
Lepocreadium setiferoides (DE) is a member of the Family Lepocreadiidae
Subfamily Lepocreadinae and is a parasite of marine teleosts (Gibson 1996). It
was previously recorded from NB specifically Kouchibouguac River, in
Kouchibouguac National Park, in the host Morone saxitillas (Hogans 1984). L.
setiferoides was also recorded from flounders and sand dabs in the Region of
Woods Hole (Stunkard 1972, Martin 1938). Although L. setiferoides has been
recorded from Kouchibouguac River, it has never been recorded from G.
aculeatus and therefore this is a new host record for the parasite.
97
Both DB and DD are members of the Family Opecoelidae which also contains
P. angulata (DQ). These parasites are known to occur in the intestines of both
freshwater and marine fishes (Hoffman 1999).
DC is a member of the Family Lissorchiidae, which are known to infect
freshwater teleosts (Hoffman 1999). .
The remainder of the parasites collected from G. aculeatus in the sGSL (DG,
DJ, DK) were not -identifiable using current keys. This may be due to DG, DJ,
DK being new species, or species previously not recorded from North America.
However, it may also be due to the parasites having irregular and distorted
shapes on slides and therefore their identifiable characteristics were obscured.
DR was the only parasite that, although distorted on the slide still had many of
its features visible but was still unidentifiable. It was collected from only two fish
at a single site. There was also an unusual food item recorded from those fish
with DR (a bright pink copepod); therefore this parasite may be an accidental
infection via its food source in G. aculeatus.
5.2 Community Ecology
5.2.1 Ectoparasites
The monogenean Gyrodactylus sp., was the only parasite known to co-occur
with the other parasite species, and then only in very low numbers. The similarity
patterns among the fish of the parasite infracommunity Cluster and nMDS closely
mirrored that of the metacommunity total abundance and presence/absence
98
results. All three levels of analysis essentially divided the ectoparasite data
along a similar line, the presence or conversely absence of the copepod
Thersitina gasterostei.
The total abundance data left Richibucto grouped on its own due to the
presence of Argulus sp. Thes rest of the sites divided into two main groups
based on low numbers (<10) and high numbers (>25) of ectoparasites. Baie
Verte was grouped in with Murray Harbour, River Phillip and Cocagne because
of the presence of Gyrodactylus sp. However, the other two levels of analysis,
the metacommunity presence/absence data and the infracommunity level data
both grouped Richibucto and Baie Verte together based on the presence of T.
gasterostei.
Thersitina gasterostei has been shown to have a seasonal distribution in the
Northwest Mecklenburg, Baltic Sea, where the intensity of T. gasterostei is higher
during June and July (Zander et al. 1999). The two sites where T. gasterostei
were found were among the first sites sampled (July 8, 19), and the earlier site
had higher numbers. However, additional sites, (K, Co, Mg, C) were sampled
during the same time period, and were missing this species. This suggests that
there was some other factor not recorded in this study that influenced the
presence or absence of T. gasterostei from different estuaries within the sGSL.
5.2.2 Endoparasites
The main pattern that can be observed in the results from the three different
data sets (Infracommunity, Metacommunity Presence/absence and
Metacommunity Total abundance) is the distribution between those estuaries
99
containing either DA (B. crenatus) or DP (H. levinseni). There were only eight
instances where DA and DP co-occurred (in Baie Verte 7 of 10 fish and in Murray
Harbour 1 fish). There are two potential, and not necessarily exclusive, reasons
for this relatively low of co-occurrence. The first is that these two parasites have
different lifecycles and are therefore abundant at different times of the year.
Another explanation is that competitive exclusion is occurring between these
parasites, i.e. one parasite may be blocking the other from developing. It is
possible that these two theories do not exclude each other and that there may be
some competitive exclusion taking place during the period when these parasites
lifecycles overlap.
There is little known about the life cycles of either of these parasites. DP
(Hemiurus levinseni) is thought to have a life cycle that closely resembles that of
H. communis (Gibson & Bray 1986). This possibility could lend a biological
explanation to the low of DA and DP co-occurrence. H. communis is known to
occur throughout the year in low numbers, but it begins to increase in numbers
throughout the late summer and early fall. This peak in its lifecycle is thought to
occur in the fall (Gibson & Bray 1986). If DP has a similar lifecycle to H.
communis then that might explain why the DP begins to be recorded near the
middle of July and in August, but does not really begin to occur in very large
numbers until September. DA (B. crenatus) is thought to have a similar life
history to Hemiurus spp. (Gibson & Bray 1986), therefore no specific inferences
can be made as to when this parasite is most abundant.
However, the data
collected for this thesis indicates that DA is most abundant during mid-summer
100
and abundance begins to decline in early August. This indicates that it is life
history and difference in times of abundance that caused the difference in
occurrence times of DA and DP.
There is some evidence to support the possibility of interspecific competition
(defined as “active demand by members of two or more species at the same
trophic level for a common resource or requirement that is actually or potentially
limiting” (Miller 1967)) that would interpret the low co-occurrence of DA and DP
as the result of competitive exclusion. Competitive exclusion has been shown to
occur in other parasite communities (Chappell 1969, Cross 1934, Paperna 1984,
Thomas 1964), and when it does there are generally two characteristics of
infections are present when two parasites are involved in interspecific
competition (Chappell 1969). First when single species infections occur both
species would be distributed more widely throughout the gut (Chappell 1969).
Second, when the two parasites co-occur, their areas of infection are spatially
separated, for example one would occupy the anterior end of the intestine while
the other the rectum (Chappell 1969). DA and DP are both from the same family
(Hemiuridae) but that they are from different Subfamilies, Lecithochiriinae (DA)
and Hemiurinae (DP) (Gibson & Bray 1986) therefore providing the potential that
these parasites occur during similar seasons. Another reason is that they both
have the same geographical range and therefore tend to occur in the same areas
providing for the potential that they will occupy similar hosts over the same
spatial and temporal distribution and therefore be in direct competition with one
another. Both DA and DP are artic-boreal species, although DP is also circum-
101
polar with respect to its artic-boreal distribution and DA is not (Gibson & Bray
1986). As well, both DA and DP occupy the same niche within the gut of the fish,
the stomach.
However, in the case of DA and DP, when they occurred concurrently they
were both present in the same area of the gut, the stomach, which is the area
where both these parasites occur. As well, when only one of the parasites was
found it was still only found in the stomach. So the patterns of presence that
these two parasites exhibit when they occur together or at different times do not
indicate that competitive exclusion was a factor in their pattern of presence.
5.2.3 Relationship to environmental factors
There are several reasons for looking for correlations. It would be useful to
know whether adjacent estuaries had similar parasite infections, whether the
parasite community could be used to place fish uniquely within an estuary, and
whether there may be impacts of pollution on parasite communities.
In terms of unique parasite communities, only Richibucto sorted out, and it
was based on a single Argulus specimen that was found in the gill cavity; this
species is usually found on the outside of the body. There were numerous
situations where fish in adjacent estuaries had markedly different communities,
which might be useful in identifying fish as resident of certain estuaries.
However, there were no definitive situations – although digenean species C,E, G,
J, K and Q were restricted to a single estuary, they were not present at any sites
in a significant number of individuals. In most cases, the parasites were found in
102
20% or less of the fish present (G, J,K, Q and R), and the others were found only
in 40% (E) or 50% (C) of the fish captured.
Merrigomish estuary comes the closets to having a unique parasite
community: Podocotyle (DQ) was found in one fish, large numbers of nematodes
were found only at this site, Brachyphallus crenatus was absent (but present in
adjacent estuaries), and Hemiurus levinseni was found in 90% of fish sampled
(but was absent in adjacent estuaries). River Philip had a similar, relatively
unique distribution relative to adjacent estuaries. It was also missing the
digenean Brachyphallus crenatus, and contained large numbers of Hemiurus
levinseni (6/10 fish). This is interesting because the two estuaries located
between River Phillip and Merrigomish are Tatamagouche and Caribou and they
contain high numbers of the digenean Brachyphallus crenatus. Nine out of ten
fish in both Tatamagouche and Caribou contain B. crenatus. This unique
distribution of endoparasites could help narrow down the residency patterns of
fish collected in this area. To further narrow origin of these fish, information on
the ectoparasites found in these estuaries can be used. There were no Ergasilus
sp. collected from River Phillip, Tatamagouche, or Caribou, however, they were
colleted from six of the ten fish sampled from Merrigomish.
There were other situations in which adjacent estuaries were markedly
different in parasite communities. In Richibucto eight out of ten fish were infected
with Thersitinga gasterostei while neither the adjacent estuaries in
Kouchibouguac nor Cocagne were infected with this species. Baie Verte is
another estuary that contains T. gasterostei (3/10 fish) when it was absent from
103
the adjacent estuaries of Cocagne and River Phillip. Therefore T. gasterostei in a
three-spine stickleback could be a potential indicator of which estuary the fish
sample originated, although there are seasonal changes in its abundance that
may affect interpretation.
PEI National Park is unique in comparison to the other sites in PEI. PEI
National Park fish were infected by Ergasilus sp. (5/10 fish), as well as digenean
‘B’ (5/10 fish) in low numbers.
On a broader distribution scale, there was no correlation of ectoparasite
numbers with geographic location, and adjacent estuaries could have
dramatically different numbers of ectoparasites. The numbers of individuals and
species, although low, could not be correlated to salinity, temperature, date of
sampling, or population density. However, endoparasite numbers showed a
correlation with population sizes (r2= 0.14), and a much stronger correlation with
the number of primary jobs (agriculture, fishing, etc; Stats Canada 1996 census
data; r2= 0.6). This correlation may be due to the increase in eutrophication in
the area causing an increase in the number of snails in the area. This increase
in snails constitutes and increase in the number of intermediate hosts available
for colonization by the parasites during their reproductive stages and can
therefore cause and increase in the number of parasites available to infect fish
(Lafferty, 1997). Fish plants and aquaculture and industrial effluents in the area
may also assist in the increase in the number of parasites (Barker et al., 1994;
Billiard and Khan, 2003; Khan, 2004). This can occur because most of the
endoparasites which infect the three-spine stickleback also infect more
104
economically important fish. Therefore the increase in the number of
economically important fish in the area (due to aquaculture) could possibly
increase the number of infected host in the region that are reproducing and
therefore increase the population.
105
Total number endoparasites
10000
R2 = 0.5769
1000
100
10
100
1000
Number of primary resoruce-based jobs
Figure 38 The relationship between the number of endoparasites encountered
and the number of resource-based jobs near the estuary.
106
Chapter 6
Conclusion
The main objectives of the thesis were to:
a) describe the parasites of G. aculeatus in the southern Gulf of St.
Lawrence (sGSL),
b) compare parasite communities of G. aculeatus on two different levels
i.
at the metacommunity level, to compare parasite communities
among adjacent geographic areas, and
ii.
at the infracommunity level, compare how individual fish parasite
communities within a single estuary, and
c) evaluate use of parasite communities within populations of G. aculeatus
be used as indicators of environmental status.
6.1 Biodiversity
6.1.1 Overall
The numbers and diversity of ectoparasites found in the different estuaries
was low with an average total number of ectoparasites collected per estuary
30.45 and the average number of different species of ectoparasite collected per
estuary only 0.73. This may reflect the difficulty in identifying specific species of
Gyrodactylus. Gyrodactylus spp. were encountered in all of the estuaries, but
107
only four other species were encountered, and these were not widely distributed
or present in very high intensities Therefore the ectoparasites of the sGSL should
be studied in greater detail to determine the specific species of parasites as well
if they naturally occur in low numbers.
Digenea were the predominant type of parasite found, and most of these
parasites were new host, and potentially new area, records for the sGSL.
Digeneans accounted for thirteen new area parasite records, ten of these being
new host records. There was also the potential for a new parasite species record
with digenean ‘R’, and also the potential that G. aculeatus was not its normal
host since it was found in only one fish in Merrigomish.
6.1.2 DIVERSITAS data set
The parasite species present demonstrate that the broader community of
parasites within the southern Gulf of St. Lawrence is distinct from other
populations found in other areas of North America and England (Peddle, 2001).
Some of the distributions are affected by the glaciation of the sGSL during the
last Ice Age, and the remoteness of the area from inland refugia. This would
affect the recolonization of the area with parasites, and intermediate host
species. Brachyphallus crenatus is widely distributed throughout the sGSL, but
is absent from most drainage basins in North America, except for the Colorado
River basin (Peddle, 2001). This species is also common in England, suggesting
that its recolonization of the area may have happened from the east.
There are other species that are unique to the sGSL. Unique records found in
this study (and identified) were Lepocreadium setiferoides and Podocotyle
108
angulata. A previous collection captured the digenean Plagioporous, which is
also not found in other studied populations (Peddle, 2001). Many of the 9
unidentified digenena species are also new records, and require expertise to
identify. These species demonstrate the utility of including the sGSL collections
in the DIVERSITAS study on biodiversity.
6.2 Community Ecology
The ectoparasites and endoparasite community’s analyses indicated different
relationships among the estuaries. However, this result was not unexpected
because ectoparasites and endoparasites are dependant on different factors for
the completion of their lifecycles. Because ectoparasites have direct lifecycle
they do not require intermediate hosts (Esch and Fernándex 1993). The chance
of finding one suitable host is therefore relatively high. Conversely endoparasites
have an direct life-cycle and therefore require intermediate hosts (Esch and
Fernándex 1993). Their occurrence may therefore be “filtered” by the sequential
probabilities of the availability of theses other host species. This adds another
dimension to the method by which endoparasite communities are formed and
therefore reducing the likelihood that endo- and ectoparasite communities would
illustrate the same or similar patterns. Another, potential cause of the differences
between the ectoparasite and endoparasite community structure is the potential
affect of exposure to the environment. Ectoparasites are directly influenced by
the changes in salinity and temperature, but endoparasites are somewhat
protected by their hosts and therefore only exposed to the shifts in the external
environment during the completion of their life-cycle.
109
Both the ecto- and endoparasite analysis at the varying levels of analysis
(metacommunity total abundance, metacommunity presence absence, and
infracommunity) showed similar patterns within the specific type of parasites.
The ectoparasites were mainly divided due to high (or low numbers of parasites)
but also due to the presences (or absence) of the parasite Thersitina gasterostei.
The endoparasites were mainly divided due to the presence of either
Brachyphallus crenatus (DA) or Hemiurus levinseni (DP).
The ecto- and endoparasite loads of the fish within individual estuaries were
in many cases unique. Therefore allowing for the potential use of these parasite
loads at identifying fish from specific estuaries.
There was also a direct correlation between the number of endoparasites and
the number of primary resource based jobs in an estuary. This correlation
provides background for a potentially new tool for looking into the impacts of
these jobs on the environment, and specifically the fish populations, in the area.
6.3 Environmental Status
The estuaries that were selected had relatively low human populations, and
relatively low levels of environmental impacts. In spite of this, there was a
relationship between the amount of human inhabitation, specifically the size of
the primary resource-based work force, and the intensity of the digenean
infections. This shows some promise in terms of examining the environmental
status.
110
Beyond that, there was some limited ability to discriminate fish from adjacent
estuaries in some areas, but the parasite communities were not distinct enough
for this to be sued on a wide basis.
111
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