BIOTIC AND ABIOTIC FACTORS RELATING TO DISTRIBUTION
OF UNIONID MUSSEL SPECIES IN L-
ST. CLAIR.
A Thesis
Presented to
The Facdty cf Graduate Studie's
of
The University of Guelph
by
DAVID THOMAS ZANATTA
In partial fulfilhnent of requirements
for the degree of
Master of Science
September, 2000
O David Thomas Zanatta, 2000
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ABSTRACT
BIOTIC AND ABIOTIC FACTORS RELATING TO DISTRIBUTION OF
UNIONID MUSSEL SPECIES IN LAKE ST.CLAIR.
David Thomas Zanatta
University of Guelph, 2000
Advisor:
Professor G. L. Mackie
Relationships between biotic/abiotic factors and the distribution of unionids in
Lake St. CIair were investigated fiorn 1998 to 2000. Native fieshwater musse1 (Bivalvia,
Unionidae) populations in the lower Great Lakes have been nearly eradicated by the
invasive zebra mussel. There are o d y a few known unionid refûgia rernaining in the
Iower Great Lakes. One such rehgium was found during this study in Lake St. Clair near
the St. Clair River delta. Morphological, reproductive, and ecological traits were not
found to have any significant relationships with the change in fiequency before the zebra
musse1 invasion (1986) compared to after the invasion (1999). Using a GIS mode1 of
Lake St, Clair, distance of survey sites fiom deep water currents were found to have
significant positive correlations (P<0.001) with unionid density. These findings lead to
recommendations to help direct ficlture unionid conservation efforts.
Dr. Gerry Mackie has been my advisor for m y Masters; his mentoring has helped
to make me the researcher that 1 have becorne. 1 can only hope to mode1 my career to be
like his. Funding for this project came £kom the Endangered Species Recovery Fund and
its CO-sponsors - World Wildlife Fund Canada, the Canadian Wildlife Service of
Environment Canada, and Canada' s Millenniurn Partnership Program. Also supporting
this study was h d i n g fiom NSERC (Operating grant #801-93). Thanks go to Dr. Bob
Bailey and Dr. Beren Robinson for being on my committee and providing comrnents and
help with putting this study together. A huge thank you goes to Daelyn Woolnough for
creating the GIS database of Lake S t Clair. Without her contribution Chapter 2 would
not have been written; Daelyn will be a CO-authorfor any paper that cornes fiom Chapter
2. Josephine Archbold, Chad Boyko, Kelly McNichols, and Susan Reynolds were my
invaluable field assistants in the summers of 1998, 1999, and 2000. Janice Metcaife-
Smith, Shawn Staton, and Joanne Di Maio of Environment Canada - National Water
Research Institute - Canada Centre for Mand Waters (NWRI-CCIW) have my gratitude
for thek assistance in teaching me and the field assistants to identie Ontario unionid
species. Don MacClendon of Ontario Ministry of Natural Resources (OMNR Wheatley)
and Erling Holm of the Royal Ontario Museum (ROM) contributed data on fish species
in Lake St. Clair. My parents deserve huge credit for always supporting me and keeping
me excited to continue learning. Finally Colleen (even though she thinks clams are
boring! !!) gave me constant support, insight, and affection.
TABLE OF CONTENTS
Acknowledgements
Table of Content
List of Tables
List of Figures
General Introduction
Study Area
Chapter 1: Survival and Recolonization Mechanisms of Unionid Mussel Species in
Ontario
9
10
Introduction
Methods
Lake St. Clair Unionid Surveys (Field Coliections)
Summer 1998
Surnrner 1999
Spring 2000
Data Collected fiom the Literature
Data Anaiysis
Transplantation Experiment
Results
Lake St. Clair Unionid Surveys
Summer 1998
Summer 1999
June 2000
Table of Contents continued
Analysis of Morphological, Reproductive, and Ecological Traits Related
to Unionid Survivai in Zebra Musse1 Irnfested Waters
25
Analysis of Wty in Ontario Unionidae
29
Transplantation Experiment
31
33
Discussion
A Unionid Refigium in Lake St. Clair
33
Morphological, Reproductive, and Ecological Traits Related to Unionid
Survival in Waters Infested with Zebra Mussels
36
Rarity of Ontario Unionid Species in kelation to Morphological,
Reproductive, and Ecological Traits
38
Unionid Transplantation Experiment
39
Recommendations for Unionid Recoveq
41
Tables
Figures
Chapter 2: Relationship of Wind-driven Water Current Patterns with the Distribution of
76
Unionid Musse1 Species Persisting in Lake St. Clair, Based on GIS.
Introduction
77
Methods
79
Creation of the Lake St. Clair GIS Model
79
Querying the GIS database to determine the relationship between wind80
driven currents and unionid densities
Results
82
Discussion
Tables
Figures
iii
Table of Contents continued
Literature Cited
Appendices
Appendix 1: Locations and descriptions of sites surveyed on Lake St. Clair.
111
Appendix 2: Matrix of rnorphological, reproductive, and ecological traits used in
discriminant fùnction analyses.
117
Appendix 3: Matrix of morphological, reproductive, and ecological traits used in
discriminant firnction analyses of unionid conservation rankings.
119
LIST OF TABLES
Chapter 1:
Table 1: Breakdown of discriminant function analyis grouping variables and Lake St.
Clair unionid species group memberships.
44
Table 2: Relationships between change in unionid species fiequencies (fiom 1986 to
1999) and traits.
46
Table 3: Cornparison of the structure coefficients of the discruninant function analyses
grouping unionid species (as increasing, stable, or decreasing) with the 10 morphological,
reproductive, and ecological traits. Discriminant function analysis number (e.g. DFA 1)
corresponding to order which they are presented in the results.
47
Table 4: Structure coefficients of rnorphological, reproductive, and ecological traits of
unionids in Lake St. Clair with h c t i o n s corresponding to Figure 11.
48
Table 5: Structure coefficients of morphological, reproductive, and ecological traits of
49
unionids in Lake St. Clair with functions corresponding to Figure 12.
Table 6: Structure coefficients of morphological, reproductive, and ecological traits of
50
unionids in Lake St. Clair with functions corresponding to Figure 13.
Table 7: Structure coefficients of morphological, reproductive, and ecological traits of
51
unionids in Lake St. Clair with functions corresponding to Figure 14.
Table 8: Structure coefficients of morphological, reproductive, and ecological traits of
52
unionids in Lake St. Clair with functions corresponding to Figure 15.
Table 9: Structure coefficients of morphological, reproductive, and ecological traits of
53
unionids in Lake St. Clair with functions corresponding to Figure 16.
Table 10: Structure coefficients of morphological, reproductive, and ecological traits of
54
unionids in Lake St. Clair with fkctions corresponding to Figure 17.
Table 11: Results of Tukey's Multiple-cornparison post-hoc test indicating significant
differences in mean number of months present between 5 transplanted species in Lake St.
.
Clair.
55
Chapter 2:
Table 1: Correlations behueen % time sites are greater than various distances (arcsine
transformed) and unionid densities (l/x+l tnuisformed). n=89 sample sites.
89
LIST OF FIGURE%
Chapter 1:
Figure la: Map of Lake St. Clair showing major landmarks, 1999 sampling sites, and
bathymetry.
56
Figure Ib: Close-up map of the northeast corner of Lake St. Clair and the St. Clair River
57
delta.
Figure 2: Map of Lake St. Clair showing unionid density b e r person hour) at 1999
sampling sites.
58
Figure 3 : Cornparison of the mean number of unionids found per site at different depths
in Lake St. Clair. Error bars show 1 standard error.
59
Figure 4: Cornparison of the mean and total number of unionid species found at different
depths sarnpled in Lake St. Clair. Error bars show 1 standard error.
60
Figure 5: Mean number of unionids found per person hour in Lake St. Clair during 1999
sarnpling period. Error bars show 1 standard error.
61
Figure 6: Percentage of sites where each unionid species was found during 1999
62
sampling penod.
Figure 7: Mean number of unionids found per person hour in Lake St. Clair during 2000
sampling penod. Error bars show 1 standard error.
63
Figure 8: Percentage of sites where each unionid species was found during 2000
64
sampling period.
Figure 9: Mean number of unionids found per m2 at sites sampled during 2000 sampling
65
period on Lake St. Clair. Error bars show 1 standard error.
Figure 10: Change in relative fiequencies of unionid species in Lake St. Clair fiom 1986
(before zebra mussel invasion) to 1999. Note large shift in some species fiequencies.
66
Figure 11: Discriminant fünction analysis of percent change in relative fiequency of
unionid species in Lake St. Clair fiom 1986 to 1999 and unionid traits. The numbers
67
correspond to species s h o w below.
Figure 12: Discriminant function analysis (DFA) of percent change in relative fiequency
of unionid species fiom 1986 to 1999 and unionid traits @FA run without Fusconaia
flavu case because it had been rnisclassified in previous DFA). The numbers correspond
68
to species shown below.
Figure 13: Discriminant function analysis of percent change in relative fiequency of
unionid species in Lake S t Clair fiom 1986 to 1999 and unionid traits. Groups
membership for DFA was determined by which percentile species change in relative
fiequency belonged. The numbers correspond to species shown below.
69
Figure 14: Discriminant function analysis of change in relative frequency rankings for
unionid species in Lake St. Clair from 1986 to 1999 and unionid traits. Group
membership for the DFA was detennined by wtiich percentile the species change in
relative fiequency ranking belonged. The numbers correspond to species shown below.
70
Figure 15: Discriminant function analysis of change in relative fiequency rankings for
unionid species in Lake S t Clair fiom 1986 to 1999 (groups selected by species
increasing in rank by more than 6 positions, changing less than 6 positions, and
decreasing by more than 6 positions) and unionid traits. The nurnbers correspond to
species shown below.
71
Figure 16: Discriminant function analysis of Ontario conservation ranks for al1 unionid
species found in Ontario and unionid morphological, reproductive, and ecoIogicai traits.
72
Numbers correspond to species below.
Figure 17: Discriminant fùnction analysis @FA) of simplified Ontario conservation
ranks for al1 unionid species found in Ontario and unionid morphological, reproductive,
73
and ecological traits. Numbers correspond to species below.
Figure 18: Cornparison of the mean nurnber of months unionids were recovered for each
replicate corral in Lake St. Clair and McGregor Creek transplant sites. Significant
differences between lake and creek sites (P<0.00l), but no significant differences
74
between replicates (P>0.05). Error bars show 1 standard error.
Figure 19: Cornparison of the rnean number of months that unionid species were present
in Lake St. Clair and McGregor Creek corrals. Significant differences between unionid
species in lake and stream (Pc0.001). See Table 11 for results of post-hoc tests. Error
75
bars show 1 standard error.
Chapter 2:
Figure 1: Map of Lake St. Clair showing major landmarks, 1999 sarnpling sites, and
bathymetry.
90
Figure 2: Map of Lake St. Clair showing selected (over water >2 m) and unselected (over
water R m) North and Northeast wind driven currents (adapted from Ayers 1964).
91
Figure 3: Map of Lake St. Clair showing selected (over water >2 m) and unselected (over
water a m) East and Southeast wind driven currents (adapted from Ayers 1964). 92
vii
Figure 4: Map of Lake St. Clair showing selected (over water >2 m) and unselected (over
water -3 m) South and Southwest wind dnven currents (adapted from Ayers 1964).
93
Figure 5: Map of Lake St. Clair showing selected (over water >2 m) and unselected (over
water -3 m) West and Northwest wind driven currents (adapted fiom Ayers 1964).
94
Figure 6: Mean percent time that wind blew during ice-fiee months on Lake St. Clair.
Enor bars show 1 S.E.
95
Figure 7: Map of Lake St. Clair showing unionid density (per person hour) at 1999
sampiing sites.
96
Figure 8: Map of Lake St. Clair showing percent time 1999 sampling sites are more than
1 km fiom deep-water currents.
97
Figure 9: Map of Lake St. Clair showing percent time 1999 sampling sites are more than
2 km fÏom deep-water currents.
98
Figure 10: Map of Lake St. Clair showing percent time 1999 sampling sites are more than
3 km fiorn deep-water currents.
99
Figure 11: Map of Lake St. Clair showing percent time 1999 sampling sites are more than
3 -5 km fkom deep-water currents.
1O0
Figure 12: Map of Lake St. Clair showing percent time 1999 sampling sites are more than
4 km fiom deep-water currents.
101
Figure 13: Map of Lake St. Clair showing percent time 1999 sampling sites are more than
5 km fiom deep-water currents.
102
Figure 14: Map of Lake St. Clair showing the degree 1999 sampling sites are being
afCected deep-water currents (created by calculating the mean percent time 1999
sampling sites are more than 1,2,3,3.5,4, and 5 km from deep-water currents). "Most
afiFected sites" are 0.0 - 17.2% time unaffected, "least atTected sites" are 68.7- 85.8%
time unaffected by deep-water currents.
103
Figme 15: Map of Lake St. Clair showing the degree historic sampling sites (Pugsley et
al. 1985) are being affected by deep-water currenl (created by calculating the mean
percent time 1999 sarnpling sites are more than 1,2,3,3.5,4, and 5 km fiom deep-water
currents). "Most affected sites" are 0.0 - 17.2% time unaected, "least affected sites" are
104
68.7 - 85.8% tirne unaffected by deep-water currents.
viii
GENIERAL INTRODUCTION
The Unionidae (Phylum: Mollusca, Class: Bivalvia) is a family of fieshwater,
Saunal bivalves found throughout the world.
Unionid mussels have radiateci into
fieshwater lakes and rivers since at least the Triassic period (Bogan 1993). Unionids
have inhabiteci lakes and rivers in Canada since the iatest Pleistocene glaciation, which
g
foot and
ended more than 10 000 years ago (Graf1997). They burrow by a n c h o ~ their
the anterior portion of their shel1 into soft or coarse substrate. The posterior portion of
the shell remains exposed, allowing the incurrent siphon to draw water oves the gills,
which filter plankton in the process (Pannalee and Bogan 1998). Unionidae have a
unique M e history; they have an obligate parasitic lamal stage on fish or amphibians.
Larval unionids or glochidia are brooded in the gill marsupia of the fernales. In order to
develop to the juvenile stage the glochidia must attach to the gills (some species attach to
the skin or fins) of a suitable host species. The glochidia parasitize the host for a short
period, metamorphose, and drop off to begin life as juveniles, provideci they land in a
suitable habitat (Parmalee and Bogan 1998).
North A m e h has the world's greatest diversity of Unionidae. Of the 297
recognized taxa in North America, 213 (72%) are considered endangered, threatened, of
special wncem, or extinct (Williams et al. 1993). As many as forty species are listed as
o c c h g within Ontario (Clarke 198 1). Metcalfe-Smith et al. (1 998% 1998b) found that
23 (57.5%) of the species found in Ontano muid be ranked S2 (very rare) to SH
(historicai; no occurrences verified in last 20 years) using COSSARO (Cornmittee on the
Statu of Species at Risk in Ontario) criteria
Twelve species could be ranked as
extremely rare (S 1) with 5 or fewer occurrences in the province. Only 11 (27.5%) of the
species occurring in Ontario were listed as common (S4) or very common (S5). Most of
the very rare species (S2 or lower) in Ontario are found in the most southem part of
Ontario, known as "Carolinian Canada," in the Lake St. Clair/Lake Erie watersheds
(Carolinian Canada 1999). The Sydenham and Thames Rivers (in the Lake St. Clair
watershed) have the most diverse unionid faunas in Canada.
Lake St. Clair has historically been home to 20 species of unionids (Reighard
1894, cited in Nalepa and Gauvin 1988). However quatitative data for unionid diversity
and abundance in Lake St. Clair are scarce. It was not until 1986 that a thorough survey
of Lake St. Clair was conducted (Nalepa & Gauvin 1988). Nalepa and Gauvin (1988)
found 18 species of unionids inhabithg the lake at a mean total density of 2 m-', with
Lampsilis siliquo iden (fat mucket), Leptodea fiagilis ( h g i l e papershell), and Potamilus
alutus @ink heelsplitter) being the most abundant species.
A variety of interrelated factors have likely contributed to the decline of unionid
populations. Habitat destruction explains most declines in unionid populations over the
last two centuries (Bogan 1993). Freshwater mussel populations are very sensitive to the
dumping of municipal and industrial pollutants (Bogan 1993). Modifications of a river or
Stream channel for navigation, flood control (dâmming), or drainage have strong impacts
on unionid fauna (Bogan 1993; Vaughn & Taylor 1999; Watters 1996). Deforestation
and poor f m i n g practices contribute to increased siltation; the gills of unionids become
clogged with silt and the bivalves suffocate (Bogan 1993, Brim Box and Mossa 1999,
Moms and Corkum 1996). Creating impoundments has the potential to exclude many
fish fiom river systems, thereby making it impossible for some mussels to find
appropnate hosts for their glochidia to complete development (Vaughn and Taylor 1999,
Watters 1996). Some species of unionids have become fiinctionally extinct.
These
species will become extinct when the remaining individuals die, because their fish host is
absent or the fish have become extinct themselves, thus making it impossible for the
unionid species to reproduce (Bogan 1993).
Before the extensive use of plastics, unionids were hmrested cornmercially for
making pearl buttons.
Unionids are still harvested for the lapanese-cultured pearl
ùidustry, where they are cut and ground into beads that form the nucleus of cultured
pearls (Williams et al. 1993). It is not known how harvesting is affecthg ail unionid
species because thick-shelled, extrernely abundant species are most desired by the
cultured pearl industry. The current technique of harvesting unionids for the cuitured
peul industry is by diving (with SCUBA gear or with an air cornpressor at the sudace),
selectively collecting the desired species and not generally disturbing the substrate or
undesired unionids (Bogan 1993, Parmalee and Bogan 1998).
The most recent threat to unionid populations is the continuing expansion of nonindigenous, invading moUuscs, such as the Asian cIam, Corbiculafluminea, and the zebra
mussel, Dreissena polymorpha (Williams et al, 1993).
It has been suggested that
Corbiculafluminea competes with native unionids for resources and has caused a decline
andor local extinctions of native fieshwater mussels (Clarke 1988, Strayer 1999). The
Asian clam is a successful competitor because, unlike unio~ds,the larvae of the Asian
clam do not require a fish host for their intermediate development, and can therefore
reproduce very quickiy (Pannalee and Bogan 1998, Strayer 1999). Corbicula fluminea
has not become a problem in the lower Great Lakes because they are not tolerant of the
cold water temperatures in winter (Matthews and McMahon 1999). More detriinend to
uriionids in the lower Great Lakes is the zebra mussel. Zebra mussels, like the Asian
clam, do not require a fish host for their l a r d development. Their larvae, called
veligers, are free swimming. The veligers settle out of the water to become juveniles,
attaching themselves by a byssus to any hard surfaces (Mackie 1991). It is believed zebra
mussels were introduced Ïnto North America in 1986 through the ballast water discharge
of a transoceanic fieighter (Hebert et al. 1989). With the invasion of the zebra mussel in
1986, the extirpation of unionids appeared rapid and complete in Lake St. Clair with
viaudly no live unionids being found by 1992 (Gillis and Mackie 1994, Nalepa et al.
1996).
Presently, it is believed that most of the pre-existing unionids have been
extirpated fiom Lake St. Clair. Sirnilar observations of unionid population declines have
been made for western Lake Erie (Schloesser and Nalepa 1994), the upper St. Lawrence
River (Ricciardi et al. 1996), the Hudson River (Strayer and Smith 1996), and currently
the Mississippi River systern where the zebra musse1 has spread quickly to the Gulf of
Mexico (Tucker el al. 1993). Zebra mussels in hi& densities can kill unionid mussels:
(i) by stripping the water column of nutrients required by the native mussels, thereby
starving the unionids through cornpetition; (ii) and by settling on the unionids and
mechanically impeding the flow of water into the unionid, either blocking its incurrent
siphon or impoverishing the water entering the siphon (Baker and Hombach 1997, Gillis
and Mackie 1994, Parker et al. 1998). Schloesser et al. (1996) suggested that the
extinctions in Lake St. Clair may be permanent, and that unionids will be unable to
recover even though zebra mussel densities are presently iower than the peak densities in
1991. While there is considerable evidence that the zebra mussels will accelerate the
decline in bivalve diversity throughout North Arnerica (Bogan 1993, Ricciardi et al.
1998), it is unknown whether the elimination of al1 unionid species by exotic zebra
mussels will be permanent.
Chapter 1 of this thesis investigates the biological characteristics of unionids that
contribute to survival and recovery processes.
Part One examines the relationships
between morphological, reproductive, and ecologicai characteristics of unionid species
and the change in relative fiequencies of species between 1986 (Nalepa and Gauvin
1988) and 1999 (collected in the field), using discriminant fünction analysis. Part Two
examines the relationships between morphoIogical, reproductive, and ecologicai
characteristics of unionid species and conservation ranking of species in Ontario using
discriminant function analysis. Part Three was a transplantation study to detemiine if
species transplanted fiom tributaries of Lake St. Clair would survive in water infested
with zebra mussels.
Chapter 2 was conducted to determine if are related to the present distribution of
unionids in Lake St. Clair is related to wind-driven currents and to mode1 where other
unionid refiigia may exist, using a mode1 of wind-driven currents (Ayers 1964),
bathymetric maps of Lake St. Clair (NOAA), and field data collected by the author.
The impact of zebra mussels on species diversity of unionid bivalves is not just a
local and regional problem but rather national and continental ofie. The results of this
study will aid COSEWIC (Cornmittee on the Status of Endangered Wildlife in Canada) in
assessing the current conservation status of unionid mussels by enabling predictions of a
species' chance o f rehabilitation in the face of zebra musse1 infestation. In spite of ten
years of research in North America (Naiepa et al. 1996) and decades of research in
Europe (Stanczykowska and Lewandowski 1993): no one can Say with confidence that
the changes in bivalve diversity observed to date: (i) will be permanent, (iij will occur in
a sequence dictated by certain morphological, reproductive, life history, and ecological
traits, and (iii) will necessitate management and control to protect and conserve the many
bivalve species (especially rare and endangered species) in North America. In their 14
years in North America zebra mussels have spread from Lake St. Clair, throughout the
Great Lakes, east into the Hudson River system, and south into the Mississippi River
system (to the Gulf of Mexico) where ecological impacts have been translated into
econornic impacts for shell industries that export shells worth $40-50 U S . milliodyr
(Parmalee and Bogan 1993). The results fiorn studies here will also greatly benefit the
shell industry in the United States, which wishes to know the long-term impact of zebra
mussels and mechanisms for combating their impacts.
This includes knovlring what
species may have the best strategies for avoiding impacts and for recovering fiom zebra
musse1 infestations. By studying the long-term impacts of zebra mussels on unionids in
Lake St. Clair, we hope to be able to better predict long-term impacts in other water
bodies in North America.
STUDY AREA
Lake St. CIair is the body of water comecting Lake Huron to Lake Erie (Chapter
1, Fig. la). The lake is fed by the St. CIair River and drained by the Detroit River. It is
the srnallest lake in the Laurentian Great Lakes system.
Lake St. Clair has a
characteristic heart-shape with a maximum natural depth of 6.5 m and a surface area of
1,115 kn? (Leach 1991). Because of the lake7s shallowness it has no commercial
harbours. However, in order to accommodate heavy commercial traffic between Lake
Erie and Lake Huron, a navigation channel was dredged to a depth of 8.3 m, bisecting the
lake dong the CanadalLTS. border (Edsall et al. 1988). Leach (1991) reports that the
substrates in Lake St. CIair consist of muddy sand in the central lake and grave1 or sand
closer to shore. Prior to zebra musse1 infestation, unionid bivalves were the only hard
substrate in many areas (Nalepa et al. 1996). Currently dead unionid shells and zebra
mussels provide most of the hard substrate away from shore (Hunter and Bailey 1992,
Ndepa et al. 1996).
Lake St, C k r has three minor tributaries after the St. Clair River, the Clinton
River in Michigan and the Sydenham and Thames Rivers in Ontario (Fig. 1). The
Sydenham and Thames Rivers possess the'richest unionid fauna in Canada.
Clarke
(1992) noted that the Sydenham River System is a natural refûgium for native unionids
and protects them from the devastating impacts of zebra rnussels. As of 2000, neither
river system has shown any evidence of zebra musse1 infestation (Metcalfe-Smith et al.
1998a; persona1 observation, 2000). The Sydenham River basin has an overall length of
about 100 km, with a total drainage area of 2,735 km2 (Mackie and Topping 1988). The
Thames River drains an area of 5,830 km2,flowing through St. Mary's, Stratford,
Woodstock, London and Chatham. Extensive land drainage systems (tile draining, large
ditches or canals, and dykes) are cornmon in both river basins as much of the two basins
consist prirnarily of improved agricdtural land (Lower Thames Valley Conservation
Authority, 2000 unpublished data; St. Clair Region Conservation Authority 2000,
unpublished data; Upper Thames River Conservation Authonty 2000, unpublished data;
Mackie and Topping 1988; Moms 1996).
SURVIVAL AND RECOLONIZATION MECHANISMS
OF UNIONID MUSSEL SPECIES IN ONTARIO.
INTRODUCTION
North America has the world's
greatest diversity of Unionidae.
The
approximately 300 species found in North America have widely varying morphology, life
histones, and ecological charateristics (Williams et al. 1993).
These varying
charactenstics could provide each unionid species with different mechanisms for s w i v a l
when under stress and for recolonization afier a species has been extirpated from an area.
There is considerable variability in the morphoIogical, reproductive, and
ecological characteristics of unionids. The morphological characteristics of unionids that
have been measured include the height to width ratio of unionids (the relative girth of the
unionid), the maximum shell length, the maximum shell width, and the maximum shell
height (Clarke 198 1). Unionids Vary in shell girth fiom very thin or alate mussels, like
Leploden fragilis (Fragile papershell) with a height to width ratio of 2.0, to very obese
mussels, like Pyganodon grandis (Cornrnon floater) with a height to width ratio of 1.33.
There is also a very large range in size for unionids with some unionids reaching very
large sizes, like Lasmigona cornplanata (White heelpslitter), which have been found over
190 mm long, and othen being relatively tiny, like Villosrrfabablis (Rayed bean), which
are rarely found longer than 38 mm.
The reproductive and life history characteristics of unionids studied were the
reproductive habit of the unionid (Clarke 1981, Parmalee and Bogan 1998), the diversity
of dispersa1 agents (Parmalee and Bogan 1998), the abundance of dispersa1 agents (Don
MacClendon, OMNR unpublished data), the glochidial valve depression or elongation
(Hoggarth 1993), and the degree of hermaphroditism in the species (van der Schaiie
1970). Species of unionids fiom the subfarnily Ambleminae are generally tachytictic,
meaning that individuals are found gravid (with glochidia in their gill marsupia) for about
4 months of the year. Species tiom the subfamilies Anodontinae and Lampsilinae are
generally bradytictic, meaning that individuals are found gravid for 8 to 12 rnonths of the
year. Some species of unionids have many known glochidial host species: Pyganodon
grandis has 31 known host fish species.
Other unionids are very host specific:
Simpsonaias ambigua (Mudpuppy mussel) is only known to use the mudpuppy as its
glochidial host. Many rare unionids have few or as yet unknown glochidial host species.
Glochidial valve depression or elongation has to do with the whether a unionid attaches
to the gills or the fins of a fish. Glochidia with valve height-length values 10 represent
the morphologically depressed forms, which tend to parasitize the fins and skin of a host
fish. Glochidia with valve height-length values >O represent the elongate form and
parasitize the gills of a host fish. Some unionid species, like Elliprio dilatata (Spike),
have a large proportion of individuals that are hermaphroditic while other species are
dioecious and even extremely sexually dimorphic, like EpiobZasma torulosa rangiana
(Northern riffleshell).
Unionids are found under a wide range of ecological conditions. These ùiclude
many substrate types (Clarke 1981, Parmalee and Bogan 1998), the habitat m e s (Clarke
1981, Parmalee and Bogan 1998), and depths found (Gordon and Layzer 1989). For
example some unionids, like P. grandis, are found fkom substrates of cobble to soi? mud,
while other species, like S. ambigua, are found in very specific habitats (under large
flagstone rocks, where its mudpuppy hosts are often fouiid). Unionids are dso found in a
variety of habitats (headwaters, streams, rivers, and lakes).
Some species are very
generalized in th& distribution, like P. grandis while other species are found in specific
habitats, like Villosafabalis, which is only found in riffle zones of rivers. Unionids are
generally charactzristic of littoral and sublittoral zones in streams, nvers, and lakes, but
some species are found in deeper water. Pyganodon grandis has been fomd in water as
deep as 3 1 m, but many riffle species are rarely found in water deeper than 0.5 m.
Zebra mussels have caused a dramatic decline in unionid abundances and
distribution in the lower Great Lakes. Ricciadi et al.(1998) noted that zebra mussels had
accelerated regional extinction rates of unionids by 10-fold, fkom. 1.2% per decade to
12% per decade. Unionid surveys in 1986 (Nalepa and Gauvin 19@88),
before the zebra
musse1 invasi~n,found unionids at al1 depths of the lake in al1 subsltrate types. Gillis and
Mackie (1994) and Nalepa et al. (1996) detected the crash in the umionid populations in
Lake St. Clair. The unionid population crashes followed the expansion of the zebra
mussel population, first in the southem part of the lake then elsewhere. By 1994 there
were practically no unionids surviving at any of the historic sarnpling sites (Nalepa et al.
1996). Before this study it was unknown if any of the unionid papulation remained in
Lake St. Clair.
The primary objectives of this chapter are: (i) to deteimine if there are areas
(refugia) in Lake St. Clair where unionids have survived the zcbra musse1 invasion; (ii) to
examine the relationships between the morphological, reproductive, and ecological
characteristics of unionid species and the change in relative fiequencies of species nom
1986 (Nalepa and Gauvin 1988) and 1999 (collected in the field); (iii) to examine the
relationships between the morphological, reproductive, and ecological characteristics of
unionid species and the spzcies' conservation ranking; and (iv) to determine if species
transplanted fiom tributaries of Lake St. Clair will suMve in waters infiested with zebra
mussels.
The morphological, reproductive and ecological traits, can potentially increase a
unionid species' chance of survivd in ecologically stressed environments. These traits
rnay provide mechanisms of persistence and recolonization that offer some species a
better chance of recovery following extirpation by zebra mussels or sorne other stressful
event. 1 focus on testing the relationships between 10 traits and the change in abundance
of unionids found in Lake St. Clair. For each trait the & is that the irait is unrelated to
change in relative abundance fiom 1986 to 1999.
1.
Shell rnorphometncs, the ratio of the unionid species' maximum shell height to
maximum shell width, maximum she1l length, width, and height (Clarke 1981).
No directional hypothesis c m be easily formulated.
2.
The maximum thickness of each unionid species' shell valve (Clarke 1981). No
directional hypothesis can be easily formulated
3.
Reproductive habits, the number of months that a species is found gravid (female
found wiîh brooded glochidia in their gill marsupia). Tachytictic unionids (shortterm brooders) put less metabolic energy into reproduction and rnay have an
advantage over bradytictic unionids (long-term brooders) when put under a stress
like zebra musse1 infestation (Schioesser et al. 1996).
4.
Diversity of dispersal agents, the number of fish hosts that glochidia of each
species' of unionid are known to parasitize (Parmalee and Bogan 1998). Unionid
species with a greater diversity of dispersai agents shouid have an advantage over
unionids that are more host specific when recovering £iom population crashes.
5.
Abundance of dispersai agents: the cumulative glochidial fish host abundance, or
the cumulative mean relative fkequencies of the host fish species foimd in Lake St.
Clair for each unionid species fiom 1986 to 1998 @on MacClendon, OMNR,
unpublished data). Unionid species with more abundant fish hosts should have an
advantage over unionids that have less abundant fish hosts when recovering fiom
population crashes.
6.
The glochidial valve depression or elongation.
Hoggarth (1993) noted a
relationship between species with morphologicdly depressed glochidia and the
rarity of the species.
Unionid species with elongate glochidia may have an
advantage over species with rnorphologicaIly depressed glochidia when
recovenng fiom population crashes.
7.
The degree of hermaphroditism in a unionid species: not hermaphroditic,
occasionally hermaphroditic, or predominantly hermaphroditic (van der Schaiie
1970).
Hermaphroditic species may have advantages over dioecious species
finding a mate in low population densities.
8.
Substrate preference: substrate generalists (found living in a variety of substrates)
and substrate specialists (found living in few different substrates) (Clarke 1981).
Substrate generalists should have advantages over substrate specialists
recolonizing areas after population crashes.
9.
Habitat preference: habitat generalists (found living in a variety of habitats) and
habitat specialists (found Living in few different habitats) (Clarke 198 1). Habitat
generalists should have advantages over habitat specialists recolonizing areas
&er population crashes.
10.
Depth preference: deepwater species and shallow-water species (Gordon and
Layzer 1989). Zebra mussels may have greater negative effects on deep-water
species, because zebra mussels are found at their greatest densities in water fkom
3 to 7m-
It would be anticipated that unionid species that best survive the transplantation
would have similar morphological, reproductive, and ecological traits to species that
increased in relative fiequency in Lake St. Clair from 1986 to 1999.
METHODS
Lake St. Clair Unionid Suweys (Field Collections)
Surnrner 1998
30 sites were selected for sampling in Lake St- Clair between Puce and Belle
River (Fig. la). Ten sites were selected at 1 m, 2.5 m, and 4 m of water and were
sarnpled between June 19 and August
1998. For each site, 20 Ekman grab sarnples
were taken frorn a boat and five 1-m2 quadrats were sampled, using SCUBA or
snorkeling. Densities of unionids (live and dead) were determined. A total of 150 1-mL
quadrat sarnples and 600 Ekman grab samples were taken during the sarnpling period.
Surnmer 1999
15-minute searches were conducted at each site using mask and snorkel in
shallow water (am), and using SCUBA in deeper water (>2 m). Two people conducted
each search for unionids with SCUBA for a total of 0.5 person hows (ph) per site. Three
peopIe conducted the search when snorkeling for a total of 0.75 person hours per site. At
sites where live unionids were found, a second 15-minute search was conducted
effectively doubling the search effort (SCUBA 1 ph, snorkel 1.5 ph). See Appendix 1 for
full site descriptions and locations.
25 sites were selected in Lake St. Clair near the St. Clair River delta and Walpole
Island Indian Reserve (Fig. 1). Sites were selected at various depths frorn the beach (-4
m) to deep water (>4 m).
Five survey sites were selected according to their distance fkom shore in Johnston
Bay (Lake St. Clair) (Fig. 1b). This is a marshy area of the lake bordering on the St.
Clair River delta. The entire bay has a fairly uniform depth (around 1 m).
Three sites were surveyed for unionids in Goose Lake fiom the north shore to the
southern outflow into Johnston Bay (Fig. lb). Goose Lake is a marshy, shallow lake
(around 1 rn deep) in the St. Clair River deIta.
Four sites were surveyed near St. Anne Island (Fig. lb), another marshy area
dong the border of the St. Clair River delta. Thiay Lm2 quadrats per site were used to
survey these sites.
Twelve sites were sampled dong the western shore of Lake St. Clair near Grosse
Pointe Michigan (Fig. la). Four sites were sampled at each depth: at the shore (4 m), in
medium depths (2-3 m), and in deep water (>4 m).
Ten of the sites surveyed in the summer of 1998 on Lake S t Clair between Pi
and Belle River (Fig. la) were resurveyed in the summer of 1999 to detennine if any
natural recolonization of unionids had occurred since the site was last surveyed in the
summer of 1998. The sites that were sampled were in deeper water only, five in 2-3 m
and five in 4 m of water.
Eleven sites along the eastem shore of Lake St. Clair were sarnpled between the
mouth of the Thames River and Mitchell's Bay (Fig. la). Survey sites were selected
along the beach (-4m) and in deeper water (>2 m).
*ring 2000
Sites where unionids were found dive in 1999 (near Walpole Island; Fig. lb)
were resurveyed using quadrat sarnples (instead of timed searches) to estimate the
densities per square meter.
Data Coiiected from the Literature
Little quantitative data exists for the unionid populations in Lake St. Clair. Prior
to suiveys done in 1986 (Nalepa and Gauvin 1988)' there was little known about the
unionid populations of the lake. Earlier reports merely stated what species were present
in the lake and its watershed (Reighard 1894,cited in Nalepa and Gauvin 1988). The
relative fiequencies of unionid species collected by Nalepa and Gauvin (1988) were
calculated fiom Table 2 in their text.
Data Analysis
The species of live unionids at each site were identified, sexed, counted, and
individually measured. A voucher unionid for each species found at each site was used to
determine numbers of zebra mussels infesting its shell. Al1 unionids were cleaned of the
zebra mussels infesting their shells and returned to the lake.
The relative fiequencies of each species were calculated fiom the number of
unionids found per person hour (e.g., for each correlation, n = # of species). The relative
fiequencies were then correlated to the 10 morphological, reproductive, and ecological
characteristics of each species described in the introduction (Appendix 2).
Pearson correlations and non-parametric Spearman rank correlations were
calculated because the data were easily ranked and there were only 27 species.
Correlation coefficients were calculated to find the relationship between the unionid
charactenstics and the change in relative species fkequency between 1986 and 1999.
Univariate analyses do not necessarily capture relationships among the traits
studied. A set of multivariate discriminant function analyses @FA) were performed on
these morphological, reproductive, and ecological characteristics
in order to determine
any relationships among al1 of the traits together and the change in relative abundance of
unionid species in Lake St. Clair. In each analysis species were categorized on the basis
of whether their "abundance" increased, decreased or rernained the sarne.
Such
designations nin the risk of being arbitrarily chosen, and so a variety of categonzation
methods were used to test the robustness of any results. The DFA's below differ only in
how species were assigned to categories.
Species in DFA 1 and 2 were categorized into 1 of 3 groups: increasing, stable,
and decreasing on the basis of a greater than 75% change in relative species fiequency
fiom 1986 to 1999 as the cut-off (Table 1). Group -1 (decreasing species) were species
with greater than a 75% decrease in relative fiequency (n=10 species); group O (stable
species) were species with littie change in species £requency, between a 75% decrease
and a 75% increase (n=8 species); and group +1 (increaskg species) were species with
greater than a 75% increase (n=9 species).
Species in DFA 3 were categorized again into increasing, stable, and decreasing
species on the bais of the quartile in which each species' change in relative frequency
fell into (Table 1). Group -1 (decreasing species) were species with a change in relative
fiequency below the 25" percentile (n=6 species); group O (stable species) were species
with a change in relative fiequency between the 25" and 7 5 percentile
~
( n 4 6 species);
and group + l (increasing species) were species with a change in relative fiequency above
the 75" percentile (n=5 species).
Species categories in DFA 4 were also increasing, stable, and decreasing by using
the change in relative fiequency ranks from 1986 to 1999 (Table 1).
Group -1
(decreasing species) were species with a change in relative frequency rankings below the
25" percentile (n=7 species); group O (stable species) were species with a change in
relative fi-equency rankùigs between the 25" and 75" percentile (n=13 species); and
group +l (increasing species) were species with a change in relative frequency rankings
above the 75" percentile (n=7 species).
Species categories in DFA 5 also used Lie change in relative fiequency ranks
fiom 1986 to 1999, but with a slight modification (Table 1). Group -L (decreasing
species) were species decreasing in rank by more than 6 positions (n=6 species); group O
20
(stable species) were species changing in rank by Iess than 6 positions (n=17 species);
group +1 (increasing species) were species increasing in rank by more than 6 positions
(n=4 species).
Discriminant function analyses were used to test if species that had been least
affected by the zebra musse1 invasion shared a suite of traits different from the species
that were more detrimentally affected.
An investigation of how the morphologicd, reproductive, and ecological traits of
unionids relate to the conservation rankings of Ontario unionid species assigned by
Natural Heritage Information Centre (NHIC) was also conducted using discriminant
function andysis (Appendix 3). Each species was grouped by its conservation ranking
(S 1, extremely rare, to S5, very common), with S l=group 1 (n=1l species), S2=group 2
(n=8 species), S3=group 3 (n=6 species), S4=group 4 (n=5 species), SS=group 5 (n=4
species), etc.
Another DFA was created using three groups to increase degrees of
fieedom available to distinguish the groups. S5 (very common) and S4 (common)
species were grouped into group 1 or common species (n=9 species); S3 (uncomrnon to
rare) and S2 (very rare) were grouped into group 2 or uncomrnon species (n=14 species);
and S 1 (extremely rare) species were group 3 or rare species (n=l 1 species).
Transplantation Experiment:
A transplantation experiment was begun in rnid-August 1998 because no live
unionids were found during the summer 1998 unionid survey. Six species of unionids
were taken from the Sydenham River, McGregor Creek (a tributary of the Thames
River), and Ruscom River, al1 within Lake St. Clair's watershed.
These were
transplanted into Lake St. Clair at Tremblay Beach Conservation Area, near Stoney
Point. The six species transplanted were Actinonaias ligamentina, Arnblema plicata,
Lasmigona cornplanata, Potamilus alatus, Pyganodon grandis, and Quadrula quadrula.
Al1 six species were historïcally found in the lake (Nalepa, et al 1996). Al1 transplants
were measured and individually marked, then placed into three, 3-m x 3-m corrals in 1 m
of water, with 30 unionids in each (5 of each species). Three smaller corrals (1-m x 1-m)
were placed in McGregor Creek where twelve unionids were placed in each corral (2 of
each species). These mussels were also measured and individually marked px-ior to
placement into the creek. The McGregor Creek site was used as a control to account for
handling and 'corral effects'. Unionids in the corrals were examined monthly from ApriI
to October 1999 and A p d to June 2000, al1 corralled unionids were measured and any
zebra mussels infesting their shells were counted. h y dead individuals were removed
from the corrais, their shell was measured, and any infesting zebra mussels counted. Any
unionids that were not found during consecutive sampling-trips (were missing fiom the
corral) were considered dead or escapees. At the end of the experiment differences in
survival rate (by nurnber of months individual unionids were consecutively present) and
zebra musse1 infestation (number of zebra mussels on unionid shells) were compared
between species and sites.
RESULTS
Lake St. Clair Unionid Surveys:
Surnrner 1998:
No Iive unionids of any species were found in Lake St. Clair between Puce and
Belle River at any of the sites sampled, at any depth. AU empty shells had living zebra
mussels still infesting them, or had byssd threads still attached to the shells indicating
that the unionids had been infested.
Summer 1999:
Live unionids were found at sites sarnpled near Walpole Island I.R., Johnston
Bay, Goose Lake, St. Anne Island, and at two sites between Mitchell's Bay and the
Thames River mouth (Fig. 2). No live unionids were found in any other areas surveyed
in the lake. Twenty-one species were found dive in the timed searches. The great
majonty of individuals and species were found in less than 1 m of water. Only one live
unionid was found at a depth greater than 2 m (Fig. 3). The majority of the species found
live were also found in cl m o f water (Fig 4). The mean nurnber of unionids found per
person hour was 45.2 (k12.5 S.E.). The most abundant species were Fusconuia frma
(Wabash Pig-toe; 18.O/person h o u k9.6 S.E.), LampsiZis siliquoidea (Fat-mucket;
13.S/person hour G .4 S.E.), and Lampsilis cardiurn (Pocket-book; 6.6/person hour k2.0
S.E.; Fig. 5). The most widely distributed species were Lampsilis siliquoidea (85.71% of
sites), Lampsilis cardium (75.00% of sites), and Ligumia nasuta (Eastern Pond-mussel;
57.14% of sites) (Fig. 6).
The mean infestation density, or the mean number of zebra mussels per unionid,
at sites in Lake St. Clair near Walpole IsIand was found to be 9 1-8 (k9.5 S.E.). Using this
infestation density found in Lake St. Clair in 1999, the zebra mussel density per m2, the
proportion of unionids colonized, and the proportion of dead unionids in a population c m
be estimated using linear regression rnodels fkom Ricciardi et al. (1995). The regression
equaions can be found in Table 4 of Ricciardi et al. (1995). The zebra musse1 density
was 5,480.0 (G48.5 S.E.) zebra musse1s/m2. The proportion of unionids colonized by
zebra musseis was 1.46 (d.10 S.E.), which translates to 100% colonization. The
proportion of dead unionids was calculated as 0.877 (H.6 19 S.E. j.
June 2000:
Thirteen species of unionids were found dive in tirned searches. The mean
number of unionids found per person hour was 21.8 (k6.7 SE.). The most abundant
species in the timed searches were Lampsilis siliquoidea (Fat-mucket; 6,9/person hour
k2.5 S.E.), Fusconaiaflma (Wabash Pig-toe; 7.9/person hour t4.9 S.E.), and h p s i l i s
cardium (Pocketbook; 2.4/person hour kl.5 S.E.; Fig. 7). The most widely distributed
species were Lumpsilis siliquoidea (100% of sites), Lampsilis cardium (62.5% of sitesj,
Ligumia nasuta (50.0% of sites), and Fusconaiafluva (50.0% of sites; Fig. 8).
Nine species of unionids were found alive in quadrat searches. The density of
unionids at sites in the vicinity of the St. Clair River delta was 0.1 7 m-2(20.04 S.E.).The
species with the highest densities in the quadrat samples were Lumpsilis siliquoidea (Fatmucket; 0.07 m'2 10.03 S.E.), Fusconaiajlnva (Wabash Pig-toe; 0.03 ni2 k0.02 S.E.),
Ligumia nanrta (Eastem Pond-mussel; 0.02 m" &0.01 S.E.),
and Lampsifi cardium
(Pocketbook; 0.02 rne2k0.0 1 S.E.; Fig. 9).
Analysis of Morphologieal, ReproductÏve, and EcologicaI Traits Related to Unionid
Survival in Zebra Musse1 Infested Waters
The relative fiequencies of the unionid species were cdculated fkom the surveys
taken during the summer of 1999. These were compared to the relative fiequencies
caiculated fiom the unionid species coIlected in a survey of Lake St. Clair in 1986
(Nalepa and Gauvin 1988), while zebra mussel populations were increasing in the lake.
The relative fkequencies of the unionid species collected during surveys in 1986 and 1999
(this study) changed drarnatically (Fig. 10). Using the overlap index (CA)of Hom (1966)
(cited fiom Metcalfe-Smith 1998c) the proportions of unionid species found in 1999
( d e r zebra musse1 invasion) overlapped 64% with the proportions of species found in
1986 (before zebra mussel invasion) indicating a change in relative fiequency. The
differences between the relative fkequencies in 1999 and 1986 were caiculated to
determine which species were most detrimentally afEected by zebra musse1 infestation.
The set of possible rnorphological, reproductive, and ecological traits that
contributed to the survival mechanisms of unionids were examined. According to the
Pearson correlation analysis, there were no significant correlations indicating that no
individuai traits contributed to persistence in the face of zebra musse1 invasion (Table 2).
Using Spearman nonparametric rank correlation analysis, the only significant correlations
were: a negative relationship between the change in relative ffequency from 1986 to
1999 and cumulative fish host abundance (FOS
16, P=0.006), and a significant negative
relationship between the change in relative fiequency from 1986 to 1999 and maximum
depth found (r-0.5 15, P=0.042) (Table 2). Maximum shell length (F-0.3 69, P=0.060),
maximum shell length (r=-0 -339, P=0.O 84), substrate preference (r=-0.3 74, P=0.054), and
habitat preference (r-0.377, P=0.052) had near significant relationships with the change
in species relative abundance fiom 1986 ta 1999.
Discriminant function analyses @FA) were used to examine relationships
between the morphological, reproductive, and ecological traits discussed earlier, and the
change in relative fiequency of unionids in Lake St- Clair fiom 1986 to 1999.
Comparïsons between the structure coefficients along Function 1 of the 5 DFA's relating
unionid traits and change in relative fiequencies can be seen in Table 3.
The groups for the first discriminant function analysis @FA 1, Table 3) were
defined by the percent change in relative fiequency of unionid species in Lake St. Clair
f?om 1986 to 1999. The separation between the groups of discriminant fimction analysis
1 (Fig. 11) were near significant according to a Wilks' Lambda chi-square test (P=0.075).
The DFA explained 91.4% of the total variance. The groups were best separated along
Function 1:
shell morphology Cr=-0.41 l), hermaphroditism (F-0.284), the number of
fish hosts present in Lake St. Clair ( ~ 0 . 2 0 4 the
) ~ change in fish host abundance fiom
1986 to 1999 ( ~ 0 . 1 8 7 )and
~ reproductive habit @=O. 164) had the highest canonical
correlations to this fiinction (Table 4). This irnplies that unionid species with a high
value for Function 1 (i.e., species that have increased in relative fiequency, or remained
stable): have a wide shell girth (Low height to width ratio), display less hermaphroditisrn,
26
have a higher number of fish hosts found in Lake St. Clair, have fish hosts that increased
in relative abundance, and have a bradytictic reproductive habit. Species that decreased
in relative fiequency would tend to have the opposites. The traits that had the highest
canonical correlations with the Function 2 were the maximum depth found (r=-0.362),
nurnber of fish hosts present in Lake St. Clair (r=-0.294), combined fish host abundance
(F-0.276), habitat preference (ranging &om specific to generai; r=-0.275),and substrate
preference (ranging fiom specific to general; r-0.238)
(Table 4). This implies that the
unionid species with a higher vahe for Function 2 would be found in shallow water, have
fewer glochidial fish hosts found in Lake St. Clair, be more habitat specific, have less
abundant glochidial fish hosts in Lake St. Clair, be more substrate specific, and have
more known fish hosts than species with low values for Function 2.
In DFA 1 Fusconaiafluva has been misclassified (grouped as a species increasing
in relative fiequency, but should be decreasing) (Figure 11). If the Fusconniaflava plot
is removed fiom the analysis @FA 2, Table 3), the differences between the groups is
statistically significant according to a Wilks' Lambda chi-square test (P=0.010)and the
DFA explained 95.8% of the variance (Figure 12). The groups were best separated dong
Function 1, with shell morphology (r-0.284)
and hermaphroditism (r=-0.213) (Table 5).
This means that unionid species with a high value for Function 1 (Le., species that have
increased in relative fiequency, or remained stable) would have a wider shell girth (lower
height to width ratio) and display less hermaphroditism than species that decreased in
relative frequency. The traits that were most highly correlated with Function 2, were the
maximum depth found @=0.327), number of fish hosts present in Lake St. Clair (r-
0.250), cumuiative fish host abundance (r-0.245), and habitat preference (ranghg fkom
specific to general; r-0.237) (Table 5). This implies that the unionid species with a
higher value for Function 2 (ie., species that increased in relative frequency) would be
found in shallower waters, have fewer glochidial fish hosts found in Lake St. Clair, have
less abundant glochidial fish hosts, be more habitat specific, and be more substrate
specific than species that remained stable or decreased in relative fiequency.
The groups for discriminant fùnction anaiysis 3 @FA 3, Table 3) were defined by
species' change in relative fkequency by percentile. The separation between the groups
of DFA 3 (Fig. 13) was not significant according to a Wilks' Lambda chi-square test
(P=0.173). The DFA explained 88.7% of the total variance. Structure coefficients
showing the relationships between unionid traits and Function 1 and 2 of the DFA are
shown ut Table 6, but do not need to be discussed further because of the non-significant
separation between the groups-
The groups for discriminant function analysis 4 (DFA 4, Table 3) were defined by
species' change in relative eequency rankings from 1986 to 1999 by percentile. The
separation between the groups of DFA 4 (Fig. 14) were near significant according to a
Wilks' Lambda chi-square test (P4.056). The DFA explained 92.1% of the total
variance. The groups were best separated dong the Function 1, but none of the traits had
high structure coefficients (Table 7). The change in fish host abundance from 1986 to
1999 (r=O. 196) and shell morphology (F-0. 121) had the highest canonicai correlations
with Function 1 (Table 7). This implies that unionid species with a high value for
.
Function 1 (i-e., species that have increased in relative fiequency, or remained stable)
have fish hosts that increased in relative abundance and have a wide shell girth. The
traits that had the highest canonical correlations for Function 2 were maximum depth
found (F-0.302), shell morphology (r=0.275), and hermaphroditism (r=0.213)(Table 7).
This implies that the unionid species with a higher value for function 2 would be found in
shallower water, have a wider shell girth, and display more hermaphroditism.
The groups for discriminant function analysis 5 (DFA 5, Table 3) were defined by
species' change in relative fiequency ranking. The separation between the groups of
DFA 5 (Fig. 15) was not significant according to a Wiiks' Lambda chi-square test
(P=0.111). The DFA explained 90.3% of the total vuiance. Structure coefficients
showing the relationships between unionid traits and Function 1 and 2 of the D F A are
shown in Table 8, but do not need to be discussed M e r because of the non-significant
separation between the groups.
Analysis of Ranty in Ontario Unionidae
Discriminant function analysis was also performed with the morphological,
reproductive, and ecological traits, and using each species' Natural Heritage Information
Centre (N'HIC), Ontario conservation ranking as grouping variables. The separation
between the groups was near significant according to a Wilks' Lambda chi-square test
(P0.069). The DFA explained 91.6% of the variance. A graphical representation of this
DFA showed best separation along Function 1, with the unionid species maximum shell
length (F-0.566), substrate preference (ranging fiom specific to general; r-0.49 l), the
maximum shell width (F-0.421), the maximum shell height (F-0.369), the number of
fish hosts present in Ontario (r==.352), and the habitat preference (ranging kom specific
to general; F-0.237) havuig the highest correlations (Fig- 16, Table 9)- This implies that
unionid species with a high value for Function 1 (Le., SI, S2, and S3 ranked species)
would be generally srnalier, be more substrate specific, have fewer glochidial fish ho&
found in Ontario, and be more habitat specific. The traits correlating best with Function 2
were shell morphology (r-0.433),
reproductive habit ( ~ 0 . 4 2 7 )number
~
of fish hosts
present in Ontario (r=0.375), glochidial gape (F-0.307),
and maximum depth found
(r=0.301) (Table 9). This implies that unionid species with a high value for Function 2
(Le., S5, S4, and S 1) would tend to have a more obese shell morphology, be bradytictic
species, have a higher number of fish hosts found in Ontario, have a nanower glochidial
gape, and be found in shallower water.
To sirnplify the discriminant function analysis described above a second DFA was
performed using fewer grouping variables. The separation between the groups was
highly significant according to a Wilks' Lambda chi-square test (P=0.009). The DFA
explained 80.5% of the variance.
A graphical representation of how the species
belonging to the three groups relate showed they were best separated dong Function 1,
by the unionid species maximum shell Iength (r=-0.548), substrate preference (ranging
fiom specific to general; ~ 0 . 5 0 1 the
) ~ maximum sheli width (r-0.442), the number of
fish hosts present in Ontario (r-0.370), the maximum shell height (1=-û.361), and the
habitat preference (ranging f h m specific to general; -0.244)
(Fig. 17, Table 10). This
implies that unionid species with a high value for Function 1 (i-e., 'iincommon" and
"rare" species or S 1, S 2 , and S3 ranked species) wouid be generaily, be more substrate
specific, have fewer glochidial fish hosts found in Ontario, and be more habitat specific.
The groups were best separated along Function 2, by shell morphology (F-0.515),
reproductive habit (r=0.471), glochidial gape (r-0.471), number of fish hosts present in
Ontario (~0.310)~
and maximum shell height (F-0.321) (Table 10). This implies that
unionid species with higher values for Function 2 (Le., "common" and "rare" species or
S5, S4, and SI ranked species) would tend to have a more obese shell morphology, be
bradytictic species, have a narrower glochidial gape, have a &her number of fish hosts
found in Ontario, and have a smaller sheli.
Transplantation Experiment
Unionids transplanted into Lake St. Clair faired much more poorly than those
transplanted to McGregor Creek. Unionids remained in fkom Lake St. Clair enclosures
for a mean 1.8 1 (k0.21 SE) months and in McGregor Creek enclosures for a mean 3.44
(M.36 SE) months.
Using a 2-way ANOVA it was found that unionid species
transplanted into the lake were recovered in significantly fewer rnonths than those
transplanted to McGregor Creek (P<0.001). There were no significant differences
between the three replicate sites in the lake or the stream (P>0.05) (Fig. 18). There were
significant differences in the number of months each species remained in enclosures
(P<O.001)(Fig. 19 and Table 11). Results fiom Tukey's Multipletomparison post-hoc
indicated that Pyganodon grandis was recovered in significantly fewer months than
Actinonaias ligamentina (P<0.001), ArnbZema plicafa (P<O.001), and Lasmigona
cornplanata (P=0.041). Quadrula quodrula was also recovered in significantly fewer
months than Actinonaias Zigamentina (P=0.001) and Arnblema plicala (P=0.001). There
was also a significant interaction between site location and species (P=0.028). No
relationship could be found between the unionid species with lower mortality and the
traits used in the DFA's.
There were very few zebra mussels infiesthg the transpIanted unionids in Lake St.
Clair, and no zebra rnussels were seen infesting any unionids in McGregor Creek. The
monthly zebra musse1 infistation density (zebra musse1 per unionid) was 0.38 (40.05
S.E.). The maximum number of zebra rnusseis seen per unionid was 5. The few zebra
mussels found on individual clams often were not found in the month after they were
initially discovered.
DIScrSSION
A Unionid Refugium in Lake St. Clair
Lake St. Clair has historically been home to a wide variety of unionid species.
There have been a s many as 27 species recorded fiom the Lake St. Clair and Detroit
River systems pnor to 1960 (Metcalfe-Smith et al. 1998a). With the introduction of the
zebra musse1 to Lake St Clair it appeared that unionids had been nearly completely
extirpated from the lake by 1994 (Nalepa et al. 1996). Since then, apparent unionid
refugia have been found in a few bodies of water (other than Lake St.Clair). Tucker and
Atwood (1995) described unionids inhabithg backwater lakes of the Mississippi River as
h w h g fewer infésting zebm mussels than unionids in the main stem of the river. They
stated that the clifference in zebra mussel infestation was a combination of lake physical
properties and interactions between waterfowl and fkeshwater drum eating the zebra
mussels. Schloesser et al. (1997) found in a 1993 study that unionids in the nearshore
waters of western Lake Erie were surviving long after unionids in deep water had been
completely eradicated by zebra mussels. They suggested that zebra mussels released
fiom unionids in nearshore areas because of unfavourable habitat conditions, such as
waves, water-level fluctuations, and ice scour. Nichols and Wilcox (1997) and Nichols
and Amberg (1999) found coexistence of zebra mussels and unionids in Lake Erie
wetlands. The theory explaining this coexistense was an interaction between warm water
and soft sediments: warm water enwuraged unionid burrowing, but soft sediments were
requVed to allow zebra mussel-infesteci clams to burrow. Schloesser et al. (1998) found
significantly smaller declines in unionid diversity and abundance at one site surveyed at
the oudlow of Lake St. Clair into the Detroit River in a 1992 study, indicating a potential
unionid refugium f?om zebra mussels. Unionids had al1 but disappeared at other survey
sites dong the Detroit River. Al1 studies that had found refùgia stated that long-term
studies would be needed to see if these refbgia would ensure unionid survival in zebra
mussel-infested waters.
The biological mechanisms for unionid species sudval in
refkgia were not addressed in any of the studies.
Live unionids were found in Lake St. Clair around the St- Clair River delta in this
study in the summer of 1999. This apparent unionid refugium fiom zebra musse1
infestation had very sirnilar characteristics to other refûgîa found in zebra mussel-infested
waters. Live unionids were found in nearshore, shallow, firm substrate, wave-swept
environments, like those described by Schloesser et al. (1997); and in wetland areas with
soft substrates, similar to those descnbed by Nichols and Wilcox (1996). Of the 21
species of unionids found live in 1999, 15 were f o n d in surveys 5om 1986 to 1994. Six
of the species found in previous surveys of Lake St. Clair were not found in 1999, thus
bringing the total nurnber of species of unionid found in Lake St. Clair since 1986 to 27
(Nalepa et al. 1996, and Gillis and Mackie 1994). Many of the species found in the
summer of 1999, but not seen in earlier studies, had been found in unpublished museurn
records fiom sites very close to those sampled in this study (Metcalfe-Smith et oz. 1998b,
Janice Metcalfe-Smith, Environment Canada, persona1 communication October 1999). A
large proportion of the species found in Lake St. Clair in 1999 around Walpole Island are
among the most rare in al1 of Canada
These rare species include:
the Northern
Riffleshell (Epioblasma torulosa rangiana), listed as endangered in the United States
(Parmalee and Bogan 1998) and Canada (Staton et al. 1998); the Wavy-rayed
Lampmussel (LampsilisfascioZa), d s o listed as endangered in Canada (Metcalfe-Smith et
al. 1999a); the Round Hickorynut (Obovaria subrotunda), S 1 ranked in Ontario and
listed as a species of special concem in North America; and the Kidneyshell
(Pfychobranchusfmciolaris), SI ranked in Ontario. The uniqueness of the unionid fauna
around the St. Clair River delta merits further monitoring to see if this deka can continue
to act as a refugium for rare and endangered species of unionids.
Zebra musse1 infestation at the sites surveyed in 1999 was close to the threshold
level for extirpation of unionids at 92 zebra mussels per unionid. Ricciardi et al. (1995)
described a density of 6000 m*2or 100 zebra mussels per unionid as the point where
unionid mortality surpasses 90% and extirpation becomes inevitable. However a number
of sites had zebra mussel densities considerably lower than the mean of 92 zebra rnussels
per unionid; some of the wave-swept, sand bottom sites had as few as 11 zebra mussels
per unionid.
Monitoring of the unionid refugium around the St. Clair River delta continued in
June 2000. Timed searches in 2000 found very similar species £?equencies as in the
summer 1999 sampling penod. Sites in Johnston Bay and Goose Lake had considerably
lower densities in 2000, when compared to the 1999 data. Large numbers of fairly fkesh
dead shells and an absence of many live unionids indicated population decline. The
decline in unionid density in this area rnay have been attributed to zebra mussels killing
off a large proportion of the population; or to increases in rooted macrophyte growth,
which perhaps had a harrnfid affect on the unionid population.
Other factors like
inexperience in unionid sampling (in 2000) by summer assistants and poor sampling
conditions (e-g., cold water and reduced visibility due to wave action stimng up bottom)
during the sampling period may also have contributed to the lower densities of unionids
found.
Quadrat sampling at sites where unionids were found in the 1999 sampling period
found sparse, but patchy densities in the unionid population.
Highest densities of
unionids were dong sand bottom. The unionid densities per square meter (0.17 me2M.04
S.E.) were similar to densities of 0.2
d found at nearby historical sites prior to zebra
mussel infestation at sites close to the St. Clair River delta (Nalepa and Gauvin 1988,
Nalepa et al. 1996). It appears that there has been little to no change in unionid density in
Lake St. Clair near the St. Clair River delta due to zebra mussel infestation of unionids.
However, continued monitoring of M s area is needed to see if uiionids continue to
persist with zebra mussel infestation.
Morphological, Reproductive, and Ecological Traits Related to Unionid Survival in
Zebra Musse1 Infested Waters
Deciding how to group the unionid species in terms of which species increased,
remained stable, or decreased in relative frequency f?om 1986 @re-zebra musse1
invasion) to 1999 posed a problem.
The method of using the change in fiequency
potentially introduced a significant eRect due to sampling error into the discriminant
function analysis (DFA). Dominant species in Lake St. Clair would require a very large
change in relative fiequency to be considered increasing or decreasing; while rare species
in the lake would require a very smdl change in relative fiequency to be considered
increasing or decreasing. The discriminant fünction anaiyses indicated that only the
change in fish host abundance in Lake St. Clair had any relationship with how the species
of unionids changed in fiequency (Fig. 14, Table 6 ) . Unionid species that had an increase
in fish host abundance in Lake St. Clair since 1986 had an increase or remained stable in
relative fiequency. However, even this relationship was weak, with the structure
coefficients being only 0.196. Zebra mussels are known to have changed entire lake
ecosystems (Nalepa et al. 1999), including the fish populations: some fish species were
aided because of the increase in prey items (Le. Freshwater D m ; Morrison et al. 1997)
and others were harmed by the destruction of spawning grounds (i-e. Walleye;
Fitzsimmons et al. 1995). An increase in a unionid species' fish host abundance would
mean that more glochidial hosts would be present and would potentially boost the
number of gfochidia that paratize a host and after a penod of time increase that species'
population size.
The resdts £kom the Spearman correlation had very similar results to DFA 3 (see
Table 2 and Table 3), indicating that greater host abundance, shallow water depth
preference, smaller shell size, and an increase in host abundance from 1986 to 1999, may
al1 have relationships with species increasing in fiequency.
Reasons for why species have increased, remained stable, or decreased in relative
fiequency in Lake St. Clair since the zebra musse1 invasion remains somewhat unclear.
The structure coefficients of the traits to the iùnctions separating the increasing, stable,
and decreasing groups were weak. Therefore, it is possible that other unknown unionid
traits may influence why unionid species were surviving zebra mussel infestations in the
unionid refugia in Lake St. Clair.
There is little information on the physiological
characteristics of individuai unionid species in the literature, .althou& Baker and
Hornbach (1997) investigated the physiological effects of zebra mussels on two unionid
species (Adinonaias Iigamentina and Amblema plicata). It was found that zebra mussel
infestation causes symptoms of starvation in unionids and that the two species were
affected unequally. The unionid population around the St. Clair River delta was not well
sampled historically (Naiepa and Gauvin 1988).
It is possible that the relative
fiequencies of the unionid species in that area have not changed significantly since zebra
mussels were introduced into the lake.
Rarity of Ontario Unionid Species in Relation to Morphological, Reproductive, and
Ecological Traits
The discriminant fiinction analysis found that rare Ontario unionids (Le. SI
ranked species) were smaller, required more specific substrates, and had fewer known
fish hosts than the more cornmon unionids (i.e. S4 and S5 ranked species). Finding that
Epioblarma triquetra,
rare species are often small (e.g. Epioblma t u d o s a rangzgranay
and Villosafabalis) should be treated with caution, however, because it may reflect a bias
in sampling favouring larger easier to find species over smaller species.
Many rare species use specific substrates: for example, the Mudpuppy Musse1
(Simpsonaias ambigua) is almost always found under flat rocks where its glochidial hosî,
the mudpuppy, is often found (Parmalee and Bogan 1998); the Northem RiffleshelI
(Epioblasma tonilosa rangiana), Snuffbox (Epioblasma rriquetra), and the Rayed Bean
(VilIosafubalis) are all o d y found in nffle habitats in a grave1 substrate. Many of these
nnie habitats are becoming more and more rare with the building of dams or siltation
causing these subspate specific species to disappear (Watters 1996, Brim Box and Mossa
1999).
Having a large variety of glochidial hosts allows a species some choice or
enhances chances of finding an appropriate host. The Giant Floater ( P y g m d o n grandis)
has 3 1 species of known fish hosts in Ontario (Metcalfe-Smith et al. 1998a). Being a
host generalist allows P. grandis to be one of the most comrnon and widespread species
of unionids in North Amerka with a range fiom Central America to the Arctic (Parmalee
and Bogan 1998). in contrast, many species of rare unionids have relatively few fish
hosts. Some species of Epioblasma have CO-evolvedwith only one fish host in a very
limited range (Parmalee and Bogan 1998). In many cases when the fish host was
removed fiom an area by damming or by pollution, the unionid species became extinct
when the remaining adult population died (Vaughn and Taylor 1999, Watters 1996,
Bogan 1993).
Unionid Transplantation Experiment
Unionids species transplanted to Lake St. Clair from lotic habitats in the
Sydenham River, McGregor Creek, and Ruscorn River had significantly higher mortality
than the species transplanted to the McGregor Creek control site. It appears that the
39
transplanted lotic species, although histoncaily found in the lake, generally did not do
well when transplanted to the lake. The difference in mortality may be due to subtle
differences in physical habitat that are very important to consider when transplanting
unionid species (Cope and Waller 1995). Hïnch et al. (1986 and 1989) found that a
mussei's response to relocation into a new environment was strongly influenced by its
previous environment. Transplanted mussels, particularly older individuals, may never
completely acclimate to the target habitat if it is different fiom the source habitat (Cope
and Waller 1995). The unionids transplanted to the lake were generally larger, older
individuals, approaching maximum s& for the species. The lake habitat may have been
too different ecologically fiom the original lotic habitats for many of the transplanted
unionids to survive. Perforrning a similar transplant with younger unionids could test this
age-related hypothesis. McGregor Creek is not especially different fiom the stream
environments that the unionids were transplanted fkom. This would explain the relatively
low mortality at the McGregor Creek site.
No relationship could be found between the unionid species with lower mortality
and the traits used in the DFA's. If more unionid species could have been transplanted
perhaps a relationship could have been found.
The small numbers of zebra mussels found at the Tremblay Beach site of Lake St.
Clair could indicate that the site was not suitable for zebra mussels. The few zebra
mussels found on the unionids in one month were offen gone by the next date the
unionids were checked. Zebra mussels are known to dislodge from their substrate if it is
unsuitable for them, and translocate to a more suitable area (Schloesser et al. 1997).
Hamilton et al. (1997) f o d that survival of relocated mussels could be enhanced
if trançplanted species are placed in suitable species-specific substrates. The unionid
species relocated in this study a i l originated fiom a gravel-mud substrate and were
relocated to a sand substrate in Lake St. Clair or a gravel-mud substrate in McGregor
Creek. The species that survived best, Actinonaias ligamentina and Amblema plicata,
were substrate generalists capable of surviving in almost any substrate, while the species
that had highest mortality (Pyganodon grandis and QuadruZa quadi-ula) were more
substrate specific, found mostly in mud and gravel, respectively (Parmalee and Bogan
1998). nie mortality of al1 the transplanted species was much lower in the McGregor
Creek site, perhaps because the substrate was very similar to the substate that they were
transplanted eom.
Recommendations for Unionid Recovery
Continued m o n i t o ~ yof unionid refigia in zebra mussel infested waters, like
those found in Lake St. Clair in 1999, will be necessary to determine if unionids will
continue to survive in these areas. Because the structure coefficients of the traits to the
h c t i o n s separating the increasing, stable, and decreasing groups were so low there may
be other unionid traits that have not been measured that were having an effect. Other
unionid species traits that could be addressed in the fiiture are physiological traits like fat
reserves of each species, how motile a species is, and overlap of diet of each species with
zebra mussels. It is possible that abiotic factors ailow the unionid refugium in Lake St.
Clair to persist, such as physical characteristics of the lake including current and water
depth, which will be investigated in Chapter 2. If unionid populations are to recover in
zebra mussel-infested waters, refugia would be the most appropriate areas to begin
recolonization experirnents.
The physical and chernical properties of the refûgia need to be examined in detail
to determine why they can better support unionids compared to other parts of the lake.
The features that differ most fiom the rest of the lake are: current patterns affected by
winds and parent streams; substrate types as af5ected by water velocities and deposition
by parent streams; water temperatures; substrate stability; and water pollution sources.
Some of these factors are addressed in Chapter 2.
Rare unionids in Ontario tend to be smaller, require more specific substrates, and
have fewer known fish hosts than more cornmon unionids. Sarnpling rnethods looking
for smaller species should ensure that there is reduced sampling bias toward finding
mostly larger species. Appropriate substrate types for rare species should be identified
pnor to attempting to recover the species. Also, one should ensure that any species that
are recolonizing by being transplanted into new environrnents, be placed into their
appropriate substrate.
Recovery plans for rare unionids should be developed in
conjunction with recovery plans for their appropriate fish hosts, to ensure that
reproduction is successfùl. If fish hosts are unknown, then studies need to determine the
species of fish hosts, and their abundance in the area selected for unionid recovery.
For transplantation experiments to work in conservation and recovery plans for
unionid species, species that have specific substrate requirements need to be transplanted
to waters with appropriate substrate or rnortality rates will be high. Also, if reproduction
of the species is to occur in transplanted unionids, the species' glochidial fish hosts will
need to be present. Younger unionids may be better able to a c c h a t e to a new habitat
than older, Iarger unionids (Cope and Waller 1995). Therefore younger, smalIer unionids
should be selected as candidates for transplantation over older, larger individuals.
Unionids are declining alarmingly throughout North Arnerica, and are the most
imperiled faund group in North Arnerica (Williams er al. 1993). Although zebra mussels
have eliminated unionids fiom most of the waters within the lower Great Lakes, this
study has brought M e r evidence that unionids c m coexist with zebra mussels in some
shallow waters. With these recomrnendations for recovery of unionids, plans can now be
devised to help rare unionids to, if not retum to historicai population sizes and ranges, at
least persist in the face of invasion by exotics, such as zebra mussels.
Table 2: Relationships between change in unionid species fiequencies (fiom 1986 to
1999) and traits.
Pearson correlation (r)
Spearman correlation
with
change
in
species
(rho)
with change in
Traits
frequency 1986-1999
species frequency 19861999 (n=27)
(1147)
Change in Fish Host
-169
.27 1
Abundance 86-99
Combined fish host
abundance
Glochidial gape
Habitat preference
Hermaphroditism
Max depth found (m)
Max Height
Max Length
Max Width
Number of fish hosts present
in Lake St. Clair
Number of known fish hosts
Reproductive habit
Shell morphology (MW)
Sheli thickness (mm)
Substrate preference
Critical Value = 0.38 1
Critical Value = 0.398
Table 3: Cornparison of the structure coefficients of the discriminant fhction analyses
grouping unionid species (as increasing, stable, or decreasing) with the 10 morphological,
reproductive, and ecologicd traits. DFA number (e.g. DFA 1) correspond to order in
which they are presented in the results.
DFA 1
Relationship
with function
1 (Table 4)
DFA 2
Relationship
with function
1 (Table 5)
DFA 3
Relationship
with function
1 (Table 6)
DFA 4
Relationship
with function
1 (Table 7)
DFA 5
Relationship
with function
1 (Table 8)
Change in Fish Host
Abundance 86-99
-187
-126
-273
-196
-127
Combined fish host
abundance
.O5 1
.O29
-.199
-.O3 1
-.O3 5
Glochidial gape
-.O9 1
-.O47
--103
.O48
.O72
Habitat preference
-.O33
-.O22
-.O93
-.O50
-.O52
-284
-.2 13
-.O53
-.O29
-.O49
.O48
.O23
-207
.O19
.O 14
Max Height
-.139
-.O90
-.IO5
-.O58
.O84
Max Length
-.Il6
-.O74
-.177
-.O80
-.O48
Max Width
.O55
.O3 7
-.O92
.O30
-.O 1O
-204
-129
-.IO8
.O56
-105
-195
-127
-.O76
.O53
- 1 12
Reproductive habit
-164
-120
-.O06
-107
-198
Sheil rnorphology
-.411
-.284
-.O35
-.121
-.O99
-.O44
-.O33
--O58
.O20
-.O03
.OS 1
.O39
-.177
.O05
.O02
Traits
Max depth found
(ml
Number of fish hosts
present in Lake St.
Clair
Number of known
fishhosts
Oiw)
SheIl thickness
(mm)
Substrate preference
Significance of
separation between
groups (P-value)
% total
variance explained
Table 4: Structure coefficients of morphological, reproductive, and ecological traits of
unionids in Lake St. Clair with fiuictions correspondhgv.O Figure 1 1,
Function
Traits
1
2
Change in Fish Host Abundance 86-99
Combined fish host abundance
Glochidial gape
Habitat preference
Hermaphroditism
Max depth found (m)
Max Height
Max Length
Max Width
Number of fishhosts present in Lake St. CIair
Number of known fish hosts
Reproductive habit
Shell morphology @/w)
Shell thickness (mm)
Substrate preference
II
% variance explained by fiinction
Pooled within-groups correlations between discriminating variables and standardized
canonical discriminant functions.
Table 5: Structure coefficients of morphological, reproductive, and ecological traits of
unionids in Lake St. CIair with fûnctions correspondin :to Figure 12.
Function
Traits
1
2
-126
.O25
Change in Fish Host Abundance 86-99
Combined fish host abundance
Glochïdial gape
habitat preference
Hennaphroditism
max depth found (m)
Max Height
Max Length
M a x Width
number of fish hosts present in Lake St. Clair
Number of known fish hosts
Reproductive habit
sheIl morphology Ww)
Shell thickness (mm)
Substrate preference
% variance explained by function
I
Pooled within-groups correlations between discriminating variables and standardized
canonicd discriminant functions.
Table 6: Structure coefficients of morphologicai, reproductive, and ecological traits of
unionids in Lake St- Clair with h c t i o n s corres~ondir to Figure 13.
Traits
Function
1
2
Change in Fish Host Abundance 86-99
Combined fish host abundance
Glochidial gape
Habitat preference
Hermaphroditism
Max depth found (m)
Max height
Max Iength
Max width
Number of fish hosts present in Lake St. Clair
Number of known fish hosts
Reproductive habit
Shell morphology Oi/w)
Shell thickness (mm)
Substrate preference
% variance explained by fùnction
Pooled within-groups correlations between discriminaating variables and standardized
canonical discriminant functions.
Table 7: Structure coefficients of morphoiogical, reproductive, and ecological traits of
unioaids in Lake St. Claîr with fûnctions correspondin to Figure 14.
Function
Traits
1
2
Change in fish host abundance 86-99
Cornbined fish host abundance
Glochidial gape
Habitat preference
Hermaphroditisrn
Max depth found (m)
Max height
Max length
Max Width
Number of fish hosts present in Lake St. Clair
Number of known fish hosts
Reproductive habit
Shell morphology (h/w)
Shell thickness (mm)
Substrate preference
-
-
% variance explained by function
-
Pooled within-groups correlations between discrimina ng variables and standardized
canonical discriminant fiinctions.
Table 8: Structure coefficients of morphologicai, reproductive, and ecological traits of
unionids in Lake St. Clair with fünctions correspondir to Figure 1S.
Function
Traits
1
2
Change in fish host abundance 86-99
Combined fish host abundarce
Glochidial gape
Habitat preference
Hermaphroditisrn
Max depth found (m)
Max height
Max length
Max Width
Number of fish hosts present in Lake St. Clair
Number of known fish hosts
Reproductive habit
SheIl rnorphology (Ww)
Shdl thickness (mm)
Substrate preference
% variance explained by function
Pooled within-groups correlations between discrimina ig variables and standardized
canonical discriminant fllnctions.
Table 9: Structure coefficients of morphological, reproductive, and ecolobgicd traits of
unionids in Lake St. Clair with fimctions corresE nding to Figure 16.
Function
Traits
1
2
3
4
Glochidial gape
Habitat preference (1-specific 4-general)
Hermaphroditism
max depth found (m)
Max Shell Height (mm)
Max Shell Length (mm)
Max Shell Width (mm)
number of fish hosts present in Ontario
Reproductive habit
shell morphology (Ww)
Shell thickness (mm)
Substrate preference (1-specEic 4-general)
4.1%
Pooled within-groups correlations between discr ninating variables and standardized
canonical discriminant functions% variance explained by fünction
51.8%
25.0%
10,6%
Table 10: Structure coefficients of morphological, reproductive, and ecological traits of
;to Figure 17.
unionïds in Lake St. Clair with functions correspondinl@
Function
Traits
1
2
-.O13
-.47 1
glochidial gape
-.244
.O89
habitat preference (1 -specific 4-generai)
.O49
.OS 1
Hermaphroditism
-.192
-146
max depth found (m)
-.36 1
-.32 1
Max Shell Height (mm)
-.548
--131
Max Shell Length (mm)
-.442
-.O69
Max Shell Width (mm)
-.3 70
,310
nurnber of fish hosts present in Ontario
-471
.O29
reproductive habit
.O14
-.5 15
shell morphology (hlw)
-.150
-.2 16
SheIl thickness (mm)
-.50 1
-186
Substrate preference (1 -specific 4-general)
-
61.5%
19.0%
Pooled within-groups correlations between discrirninating variables and standardized
canonical discriminant fiuictions
% variance explained by fùnction
Table 11: Results of Tukey's multiple-cornparison post-hoc test indicating significant
differences in mean numbei of mon& present between 6 transplanted unionid species in
Lake St. Clair.
Species
Actinonaius
ligam entina
I
Lusmigona
comptanata
I
Pyganodon
grands
Quadda
quadrufa
Actinonaias
Iigamentina
Amblema
plicata
Lasrnigona
cornplanata
PotamiIus
alatus
Pyganodon
grandis
Quadrula
quadrula
-
NS
NS
-
Sig
Sig
Sig
P<O.OO 1
P<O.OO 1
P=0.03 7
Sig
Sig
P=O.OO 1
P4.00 1
NS
NS
-
-
NS
NS
-
Figure la: Map of Lake St. Clair showing major landrnarks, 1999 sampling sites, and
bathymetry.
Figure lb: Close-up map of the northeast corner o f Lake St. Clair and the St. Clair River
delta.
80 -
g
c
80-
t
Depth of Site
70-
E
g
g
(ml
=cl
50-
11-2 rn
n>2m
L
En
0
-c
E
rn
so-
40-
O
30-
3
cc
O 20-
*
ta
-
O
-
4.22
0.77
0.00
I
Walpole island Sites
0.00
~~
Mitchell's Bay-Thames River Sites
Figure 3: Cornparison of the mean number of unionids found per site at different depths
in Lake St. Clair. Error bars show 1standard error.
Mean Unionid SpecieslSite
Total Unionid Species
Figure 4: Cornparison of the mean and total number of unionid species found at
different depths sampled in Lake St. Clair. Error bars show 1 standard error.
Quadnrle quadrula
Pleurobema slntoxia
Epioblasma t o ~ l o s a
mngiana
Anodontoides femssaci~nus
Quadmla pustulose
Strvphitus unduletus
Ugumia recta
Ptychobmnchus faScriolaris
Lasmigona wstata
-œ
Q)
O
Leptodea îiagilis
œ
Elliptio diletafa
V)
iampsïis fascrOIa
n
Obovanb submtunda
Amblema plicata
Pyganodon gmndis
Vilosa iris
Potamilus alatus
tigumia nasufa
0.00
5-00
10.00
15.00
20.00
25.00
30.00
Unionids per person hour
Figure 5: Mean number of unionids found per person hour in Lake St Clair during 1999
sampling period. Error bars show 1 standard error.
Strophitus unduletus
Quedrule quadnrle
Quadrule pustuIosa
Pieurobema sintoxia
Epioblasma toruIosa mngiana
Anociontoides ierussacianus
Ligumis recta
EIIiptio dilatata
U p h o branchus fascidans
-a
O
U
4,
0,
V)
Ob ovarîe subrotunda
Lasmigona costata
Lempsilis fascida
Wllose iris
Fusconeia naM
Potamilus alatus
Ligumia nasuta
Lampsilis cardium
iarnpsilis siliquiotiea
Fipre 6: Percentage of sites where each unionid species was found during 1999
sampling period.
Leptodea lTagilis
Elliptio dilatata
Amblema plicata
Potamilus datus
t
CI
Lampsiiis cardium
0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
Unionids per person hour
Figure 7: Mean number of unionids found per person h o u in Lake St. Clair during 2000
sampling period. Error bars show 1 standard error.
Leptouéa fragilis
Eliiptio dilatata
Amblema plicata
E
Potamilus aratus
-q:
a
Q
n
Lasmrgona costata
V)
murnia nasuta
Pieumbema sintoxia
Obovaria submtunda
Larnpsifis cardium
Fusconaié fiava
Lampsilis siiquo~~dee
0.0%
10.0%
20.0%
30.0%
40.0%
50.0%
60.0%
70.0% 80.0%
90.0% 100.0%
% of Sites
Figure 8: Percentage of sites where each unionid species was found during 2000
sarnpling period.
Potemilus alatus
Fyganodon grandis
F
b+
0-00
0.02
0.04
0.06
0.08
0.1 0
0.12
Unionids per m2
Figure 9: Mean nurnber of unionids found per m2at sites sampled during 2000 sampling
period on Lake St. Clair. Error bars show 1 standard error.
Anodontojdes femssaffrénus
Quadrula pustulosa
Ptychobmnchus fasehlaris
Lasmigona costata
VilIosa iris
TiunaYla doneciformis
Relative Frequency 1999
Relative Frequency 1986
Fusconaie flava
q.ganodon grandis
Lampsirrs cardium
Uliptio dilatata
Potamilus alatus
Leptodea fiagilis
0.0% 5.0% 10.0% 15.0% 20.0% 25.0% 30.0% 35.0% 40.0% 45.0% 50.0%
Relative Frequency (%)
Figure 10: Change in relative frequencies of unionid species in Lake St. Clair from 1986
(before zebra musse1 invasion) to 1999. Note large shift in some species fiequencies.
Group % change 86-99
CV
C
.-O
g
4
x
%l!
-2'
A 1: ~ 7 5 %
increase
00
CI
-3'
s
LL
@ Group Centroids
a O:
stable species
x -1 : 275% decrease
4
- 4 - 3 - 2 - 1
0
1
2
3
Function 1
Figure 11: Discriminant function analysis of percent change in relative fiequency of
unionid species in Lake St. Clair from 1986 to 1999 and unionid traits. The numbers
correspond to species shown below.
Species
Actinonaias li@zrnentÏna
~mblema
plic>a
Anodontoidesferussacianus
EiI@tiodilatata
Epioblasma toruiosa rangiana
Fusconaiajlava
LampsilrS cardium
Lumpsilisfasciola
Lampsilis siliquiodea
Lasmigona complrmoia
Lasmigona costata
LeptodeajFagrgrlis
Ligumia nasuta
Ligumia recta
Label Number
1
2
3
4
5
6
7
8
9
1O
11
12
13
14
Species
Obliquaria refrexa
Obovmia subrotunda
Pleurobema sintoxia
Potamilus aiPtychobranchusfasciolaris
Pyganodon grand&
QuadiwIaptulosa
Quaahfaquadrula
Simpsonaias ambigua
Slrophitus urldulatrcs
Thincilla donaciformis
ïhnciiia tnrncata
VilIosa ira
Label Number
15
16
17
18
19
20
21
22
23
24
25
26
27
Group % change 86-99
@ Group Centroids
i : >75% increase
A O: stable species
x -1: >75% decrease
Function 1
Figure 12: Discriminant function analysis @FA) of percent change in relative fiequency
of unionid species fiom 1986 to 1999 and unionid traits @FA run without Fusconaia
frma case because it had been miscIassified in previous DFA). The numbers correspond
to species shown below.
Species
Actinonaias ligamentina
~ rblema
n plicita
Anodonîoidesf i s a c i a n u s
Elliptio dilatata
Epioblmma tonrlosa rangiana
Lampsilh cardium
Lampsilisfascio fa
Lampsilis sifipiodea
Lasmigona compfanata
Lasrnigona costuta
Leptodeafragi lis
Linumia
- namta
Ligumia recta
LabelNumbw Species
1
Obliquaria reflexa
Obovaria subrorunda
Pleurobema sintoxia
Potamilus alutur
Ptychobranchusfai~ciolarIS
Pyganodon grandis
Quaahla pustulosa
Quadmla quaahla
Simpsonaias ambigua
Strophitur unduiattls
Tnrncilla donaciformis
Tmncilla truncata
13
Villosa iris
Label Number
14
26
Group % change 86-99
@ Group Centroids
A 1: Species >75th
percentiIe
O O: Species btw 25th
and 75th percentile
x -1: Species <25th
percentiIe
Function 1
Figure 13: Discriminant fiinction analysis of percent change in relative fiequency of
unionid species in Lake St. Clair fkom 1986 to 1999 and unionid traits. The percentile in
which the change in relative fiequency of the species belonged deterrnined group
membership for DFA. The label numbers correspond to species shown below.
&ecies
Act inonaias ligamentina
Am blema plicat a
Anodontoidesfemsacianus
Ellbtio dilatata
Epioblasma tortdosa rangiana
Fusconaia flava
Lampsilis cardium
Lampsilis fasciola
Lampsifissiliquiodea
Lasm igona complanata
Lasmigona costata
Leptodea fragilis
Ligumia naruta
Label Number S~ecies
1
Obliquaria reflexa
Obovaria subrorunda
Pleurobema sintoxia
Potamilus alatm
Ptychobranchus fasciolaris
Pyganodon grandis
Quadrula pustulosa
Quadrula quadrula
Simpsonaias ambigua
Strophitus undulatus
Truncilla donacl~ormis
Tnrncilla truncata
Viïlosa iris
Label Nwnber
15
@
$4
n
1 Groups based on ran
ur."
@ Group Centroids
A 1: Species ranked
>75th percentile
@
0 0: Species btw 25th
and 75th percentile
U
-6
-4
-2
1
~ 2 5 t hpercentile
Function 1
Figure 14: Discriminant function analysis of change in relative fiequency rankings for
unionid species in Lake St. Clair fkom 1986 to 1999 and unionid traits. The percentile in
which the change in relative fiequency ranking of the species belonged detemiined group
mernbership for the DFA. The label numbers correspond to species shown below.
Species
Actinonaias ligamentina
AmbIema plicÜra
Anodontoidesferussacianus
EII@tiodilarata
Epiobiasma tomlosa rangiana
Fusconaiaflava
Lampsilis cardium
Lampsilis farciola
Lampsilis siliquiodea
Lasmigona cornplanata
Lasmigona costata
Leptodea fiagilis
Ligumia nasuta
Label Number Species
1
Obliquaria rej7exa
Obovaria subrotunda
Pleuroberna sintoxia
Potamilus alatus
Ptychobranchusfasciolaris
Pyganodon grandis
Quadrulapustulosa
Quadrula quadrula
Simpsonaias ambigua
Strophitus undulatus
Truncilla donaciyormk
Trunciila tmncata
VilIosa iris
Label Number
15
1 Change in Ranks
@ Group Centroids
A 1: Increase in rank
>6positions
O O: Change in rank
<6 positions
x -1: Decrease in
rank >6 positions
Function 1
Figure 15: Discriminant function analysis of change in relative fiequency rankings for
unionid species in Lake St. Clair from 1986 to 1999 (groups selected by species
increasing in lank by more than 6 positions, chaoging Iess than 6 positions, and
decreasing by more than 6 positions) and unionid traits. The numbers correspond to
species shown below.
Species
Actinonaias ligarnentina
~ m b l e m plic&a
a
Anodontoiàesferussacianus
Elliptio dilatata
Epioblasma torulosa rangiana
FusconaiaJava
Lumpsilis cmdiurn
LampsilisfmcioIa
Lampsilis siliquiodea
Lasmigona cornplanata
LaiFrnigona costata
Leptodeafiagilis
Ligumia nasuta
Ligumia recta
Label Number Species
1
Obliquaria reflexa
2
Obovariaabrotunda
3
Pleurobema sintoxia
4
Potamilus al^
5
Ptychobranchusfasciolaris
6
Pyganodon grandk
7
Quadrulap t u l o s a
8
Quadrulu quacirula
9
Sirnpsonaias ambigua
10
Slrophi'hrs undulatus
11
Tmncilla donacforma
12
Truncilla truncata
13
Villosa iris
14
Label Number
15
16
17
18
19
20
21
22
23
24
25
26
27
Ont Cons Rankings
Group Centroids
+ S5 - very common
S4 - common
* S3 - rare/uncomrnon
O S2 - very rare
x S I - extremely rare
Function 1
Figure 16: Discriminant fiuiction analysis of Ontario conservation ranks for all unionid
species found in Ontario and unionid morphological, reproductive, and ecologicai traits.
Numbers correspond to species below.
Species
Act inonaias Iigamentina
Alasmidonta marginata
Alasmidonta viridk
Amblerna plicata
Anodontoidesferussacianus
Cyclonaias tuberculata
Eltiptio dilatata
Epioblasnta torulosa rangiana
Epioblasrna triquerra
Furconaiajlava
Lampsilisfmciola
Lampsilis cardium
LumpsiZk siliquiodea
Lasmigona cornplanata
Lasmigona compressa
Lasmigona costata
Leptodea fragilis
Ligumia nasuta
Label Number Species
1
Ligurnia recta
0 & p a r i a rejlero
Obovmia subrotunda
Pleurobema sintoxia
PotamiZus alatus
PtychobranchusfascioIaris
Pyganodon grandis
Quadrulaphclosa
Quattwla quadrula
Simpsonaias ambigua
Strophitus unhuIuru~
Toxolasmaparva
TntnciZZa donuciformis
Trwtcilla truncata
Utterbackia iinbecillus
VilZosafabalîs
Villosa iris
18
Label Number
19
Unionid Species Rank
@ Group Centroids
+ 3 - Cornmon
* 2 - Uncornmon
x 1 -Rare
Function 1
Figure 17: Discriminant funetion analysis @FA) of simplified Ontario conservation
ranks for al1 unionid species found in Ontario and unionid morphological, reproductive,
and ecological traits. Numbers correspond to species below.
Speciés
Actinonaias ligamentha
A famidonta mginara
Almidonta viridir
Amblema plicota
Anodontoides ferussacianus
Cycfonaiastuberculata
EIIipfio dilatata
Epioblasma tomIosa rangianu
Epiobfasrna friquetra
Fusconaia@a
Lampsilk fmciola
Lanrpsiïk cardiunr
Lampsiik silitpiodea
Lasmigona cornplanata
Lasmigona compressa
Lasmigona costata
Leptodeafiagilis
Ligumia nasuta
Label Number Species
1
Ligumia recta
2
obliquaria refleca
3
Obmaria subrotunda
4
Pieurobema sintoxia
5
Potamilus alatw
6
Ptychobranchusfmciolaris
7
Pyganodon grandis
8
Quaahdapushdosa
9
Quadrula quadrula
10
Simpsonaias ambigua
11
Strophirus undulotus
12
Toxolasmaparva
13
TmnciZZa donacfotrnis
14
Tnrncilla tnrncata
15
Utterbackia imbecillus
16
Villosafabalis
17
Villosa iris
18
Label Number
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
Lake St. Clair-1 Lake St Clair-2 Lake St Clair-3 McGregor Cr.-1 McGregor Cr.-2 McGregor Cr.3
Sites
Figure 18: Cornparison of the mean number of months unionids were recovered for each
replicate corral in Lake S t Clair and McGregor Creek transplant sites. There were
significant differences between lake and creek sites (P<O.001), but no significant
differences between replicates within a site (P>0.05). Error bars show 1 standard error.
I
Lake S t Clair
IMcGregor Creek
P. alatus
L.
cornplanata
A. plicata
A.
Iigamentina
Q- quadrula
P. grandis
Species
Figure 19: Cornparison of the mean nurnber of months that unionid species were present
in Lake St. Clair and McGregor Creek corrals. There were significant differences
between unionid species in lake and Stream (P<O.00 1). See Table 11 for significant
differences. Error bars show 1 standard error.
RELATIONSHIP OF WIND-DRIVEN WATER
CURRENT PATTERNS ON WITH THE DISTRIBUTION
OF UNIONID MUSSEL SPECIES PERSISTING IN
LAKE ST. CLAIR, BASED ON GIS.
Zebra mussels (Dreissena polporpha and Dreissena. bugensis) have caused
major population crashes in native fkeshwater mussels (Unionidae).
It was initially
believed that unionid populations had been completely extirpated fiom the lower Great
Lakes. However, since the apparent extirpation, areas where unionids have survived the
zebra musse1 invasion have been found in a few bodies of water. Rehgia have been
found in nearshore £kmsubstrates of the Western basin of Lake Erie (Schloesser et al.
1997), in wetlands bordering on Lake Erie (Nichols and Wilcox 1997, Nichols and
Amberg 1999), areas of low flow on the Detroit River (Schloesser et al. 1998), and in
backwater lakes of the Mississippi (Tucker and Atwood 1995). Mackie et al. (2000)
found a large population of unionids in Lake St. Clair in very shallow waters around the
Walpole Island Marsh and the St. Clair River Delta. Twenty species of unionids were
found alive in the sites sampled in 1999 and 2000. The unionid refügium found ut Lake
St. Clair had many characteristics similar to other described refugia
Unionids cannot survive with high densities of zebra mussels idesting their shells
(Ricciardi et al. 1995).
Most unionids in the refugia described above have had
significantiy fewer zebra mussels infesting their shells than had been found on unionids
in other parts of the lakes or rivers before their extirpation (Gillis and Mackie 1994,
NaIepa et al. 1996, Schloesser and Nalepa 1994). A variety of interrelated factors may
explain why zebra mussels are not suniving in these apparent unionid refugia. First,
zebra mussels are not tolerant of shallow waters; they are at theh peak densities in waters
fiom 3-7 m (Claudi and Mackie 1994). Zebra musse1 veligers are passive, with their
movement controlled by water current patterns. They will settie out of the water column
a distance, dependant on current velocity, dom-curent from the parent zebra musse1
population, and so may not arrive at refugia in high densities as juveniles. In Lake Erie,
only 5% of the zebra musse1 veliger population was found at 0-2 m, 30% at 2-4 m, and
64% at 4-6 m indicating that the settlhg rates are greatest in water deeper than 2 m
(Fraleigh et al. 1993).
It can be hypothesized that unionid populations should exist in areas of low flow
and shallow water because zebra mussels do not reach extreme densities in these areas. If
this relationship can be found, it can then be predicted where other unionid refugia might
exist in the lake by determinhg the effect of wind-driven water currents on historie sites
in Lake St. Clair fiom Pugsley et al. (1985). These relationships were assessed using a
Geographic Information System (GIS) mode1 created for Lake St. Clair.
METHODS
Creation of the Lake St. Clair GIS Mode1
Data entry, manipulation, and illustration were completed on a PC using CARIS
GIS Software (Universal Systems Ltd., Fredericton Canada) and ArcView 3.0a GIS
(ESRI, USA). Three ioformation layers were considered: species distribution and density,
wind-driven currents, and bathymetry. Global positioning systern (GPS) data fkom Lake
St. Clair sampling sites of Mackie et al. (2000) (Fig. 1) was converted fkom Microsofi
Excel format into ArcView 3.0a GIS. Bathymetric and shoreline data fiom the National
Oceanic and Atmosphenc Administration USA (NOAA) were used to geo-reference the
sampling sites within Lake St. Clair.
A Universai Transverse Mercator, Zone 17
projection was used for aU data, and the datum were shifted so that al1 the data were in
World Geodetic System 1984; this daturn was selected so that data directly recorded with
the GPS could be overlayed onto the map without datum conversions. Data collected
during the 1998 and 1999 seasons were included within the attribute table for the
sampling sites so that quenes could be performed. Eight wind-driven currents (North,
Northeast, East, Southeast, South, Southwest, West, Northwest) were entered into the
ArcView 3.0a GIS by fïrst digitizuig fiom a scanned image fiom Ayers (1964) into
CARIS GIS. Since the wind-driven current maps did not have a stated projection or
d a m , a 3rdorder polynomial fit with 16 control points was found to be the best fit w i t h
the shoreline of Lake St. Clair. Afier digitizing, the data were exported fiom CARIS and
irnported into ArcView 3.0a The 1999 sampling site data, the wind-driven current maps,
bathymetry, shoreline and histonc sampling sites fiom Nalepa et al. (1996) and Pugsley
et al. (1985) were included in the GIS analysis. The sampling site data, 1999 and
historie, were displayed in a point format whereas the bathymetry, shoreline, and wind-
driven currents were al1 displayed in a line format.
Querying the GIS database to determine the relationship between wind-driven
currents and unionid densities
Al1 wind-driven currents over water greater than 2 meters were selected to
highlight the currents that would carry higher densities of zebra musse1 veligers (Fig. 2-
5). 1999 sample sites more than 1, 2, 3, 3.5, 4, and 5 km fiom the selected wind-driven
currents were selected out sequentially. These selected sites could then be considered as
sites unaffected by the currents over deeper water, and therefore thry would receive
fewer zebra musse1 veligers into the area. Each site was either afTeded or unaf5ected by
each wind-driven current. When a site was outside the distance (1,2,3, 3.5,4, or 5 km),
it was given a value of 1 (Le., unaffected 100% of time by the wind-driven current), and
when a site was inside the specified distance it was given a value of O (Le., a e c t e d 100%
of t h e by the wind-driven current). This value was then multiplied by the percent of
.
roses for an 18-year average
tune each wind-driven current pattern was o c c ~ g Wind
(1936-53) in Mt. Clemens, MI fiom Ayers (1964) were measured to find relative wind
directions in ice-fiee months (April-November) (Fig. 6). The cumulative percentage of
time that sites were unaected by wind-driven currents was calculated by adding together
the percentages calculated fiom wind roses.
Correlation coefficients between the
cumulative percentages of t h e that sample sites were unaffected by wind-driven cments
and unionid density per person h o u at each site were calculated to determine if there
were significant relationships.
To normalize the data arcsine transformations were performed on the percent tirne
sites were unaffected on wind driven currents and l/x+l transformations were perfonned
on the unionid densities per person hour.
The historic sampling sites of Pugsley et al. (1985), which covered a larger area
of the lake than the sites sampled in 1999, were selected using the same method as for the
1999 sampling sites. The percent of time unaffected by wind-driven currents was
cdculated for these sites to determine what other areas of Lake St. CIair might have
remaining unionids.
Mean percent t h e wind was coming fiom each direction was calculated fiom
wind roses in Ayers (1964) fiom ice-free months (April-November). The percent time
that winds were calm was 14.2% 3~2.6S.E.; winds less than 6.4 km/h were considered
calm conditions, because winds below this magnitude were not easily measured with the
equipment at hand (Edsall et al. 1988). The prevailing winds in the Lake St. Clair region
during ice-free months were Southerly and Southwesterly, with winds blowing fkom
these directions 13.4% +0.4SE and 13.2% H-gSE, respectively (Fig. 6).
Unionid populations exist in Lake S t Clair at sites sampled in water less than 2 m
deep around the St. Clair River delta and at two sites sampled between Mitchell's Bay
and the Thames River mouth (Fig. 7). Densities (per person hou) were highest at sites
dong the North shore of the lake bordering on the St. Clair River delta (W-Il, WI-21,
WI-22, WI-3 1, WI-41, WI-5 1, WI-52, WI-53, WI-54, W-59, in Johnston Bay (JB-1 1,
JB-12, and JB-13), and Goose Lake (GL-11, GL-12, GL-13). See Appendix 1 for site
descriptions and site coordinates.
Sites that were most often greater than 1 km fiom \hrind-men currents were sites
dong the coasts of the lake and in the St. Clair River delta (Fig. 8). The percent time that
each sarnple site was greater than 1 km fiom wind-driven currents (arcsine transformed)
and unionid density per person hour (l/x+l transforrned) were significantly correlated
(r-0.697,
P<O.OOl).
Sites that were most often greater than 2 km fiorn wind-driven currents were sites
dong the coast of the lake between Puce and Belle River, Ontario, and in the St. Clair
River delta area (Fig. 9). The percent time that each sample site was greater than 2 km
fiom wind-driven currents (arcsine transformed) and unionid density per person hour
(1/x+l transformed) were significantly correlated (-0.744,
P<0.00 1).
Sites that were most often greater than 3 km fiom wind-driven currents were sites
in the St. Clair River delta area and some sites on the coast of the lake between Puce and
Belle River, Ontario (Fig. IO). The percent time that each sample site was greater than 3
km fiom wind-driven currents (arcsine transformed) and uniocid density per person hour
(I/x+1 transformed) were significantly correlated (r-0.7 18, P<O.OO 1).
Sites that were most often greater than 3.5 km f i o m wind-driven currents were
sites in the St. Clair River delta (Fig. 11). The percent time that each sample site was
greater than 3.5 km fiom wind-driven currents (arcsine transformed) and unionid density
per person hour (l/x+l transformed) were significantly correlated (F-0.71 1, P<0.001).
Sites that were most often greater than 4 km fiom wind-driven currents were sites
in the St. Clair River delta (Fig. 12). The percent time that each sample site was greater
than 4 km fiom wind-driven currents (arcsine transformed) and unionid density per
person hour (l/x+l transformed) were significantly correlated (F-0.649, P<0.001).
Sites that were most often greater than 5 km fkom wind-driven currents were sites
in the St. Clair River delta (Fig. 13). The percent time that each sample site was greater
than 5 km fiom wind-driven currents (arcsine transformed) and unionid density per
person hour (l/x+l transformed) were significantly correlated (r-0.53 6, P<0.00 1).
The mean percent time that each sample site was greater than 1, 2 , 3 , 3.5,4, and 5
km fiom selected wid-driven currents was determined. The sites that were most often
greater thân each distance from currents were sites in the St. Clair River delta, some sites
dong the South coast of the lake between Puce and Belle River, and two sites dong the
coast of the lake between the Thames River mouth and Mitchell's Bay (Fig. 14). The
mean percent tirne that each sample site was greater than 1, 2, 3, 3.5, 4, and 5 km from
wind-driven currents (arcsine transforrned) and unionid density per person hour (l/x+l
transformed) were significantly correlated (r=-0,749, P<0.00 1).
Because of the significant conelation between the mean percent time that each
sample site was greater than 1, 2, 3, 3.5, 4, and 5 km fiom selected wind-driven currents
and unionid density per person hou, the percent time that sample sites are greater than 1,
2, 3, 3.5,4, and 5 km fiom selected wind-driven currents can be used predict where other
unionid refugia may occur.
Historic sampling sites iikely to have extant unionid
populations occur close to the St. Clair River delta, in Mitchells' Bay, and in Anchor
Bay. Figure 15 shows where the least affected historic sites (Pugsley et al. 1985) occur.
Lake St. Clair has been infested with zebra mussels for 14 years, and zebra
mussels in extreme densities have caused near-total mortality of unionids through most of
the lake (Nalepa et al. 1996). But unionids at sites sampled by Mackie et al. (2000) in
shallow water (4 m) near the St. Clair River delta, and not sarnpled in previous surveys
(Nalepa and Gauvin 1988, Nalepa et al. 1996,Giilis and Mackie 1994) still have unionid
populations. This suggests thai the unionid refugium in the shallow waters around the St
Clair River delta may be due to the site's distance from deep-water, winddriven currents.
Sampling sites with higher unionid densities tend to be M e r fiom deep-water currents
than sites with few or no Iive unionids.
Wind-dnven current patterns control the dispersal of zebra musse1 veligers
(Mackie 1991). Zebra mussel veligers are at their highest levels in waters from 3-7 m
deep (Claudi and Mackie 1993). The density of addt zebra mussels on substrates is
dependant on the density of veligers that settle out of the water columa Adult zebra
mussels in densities over 100 per unionid are known to kill unionid populations
(Ricciardi et al. 1995). Because the sites in Lake St. Clair with live unionids are far fiom
the deep-water, veliger-bearing currents, the zebra musse1 veligers are likely not settling
in high densities in the shaliow water bays near the St. Clair delta. The proximity of
many of the sites to the charnels of the delta may also be causing the sites with iive
unionids to be well flushed, also reducing the number of veligers settling in the area.
Only 5% of veliger populations were found in the top 2 m of the water column in
Lake Erie (Fraleigh et ai. 1993). Therefore, one would expect few zebra musse1 veiigers
in the water that gets into the shailow area of the lake and so few juvenile zebra mussels
would settle upon and infest unionids living in these regions. This seems to be especidly
tnie where there is a large area of shallow water (<2m) near the St. Clair River delta
Waters of other unionid refugia have many of the same characteristics as those of
the unionid refùgium found in 1999 in Lake St. Clair near the St. Clair River delta.
Tucker and Atwood (1995) described unionids inhabiting backwater lakes of the
Mississippi River as having fewer infesting zebra mussels than unionids in the main stem
of the river. They stated that the reduction in zebra mussels was a combination of lake
physical properties (low flow and shallow water) and interactions between waterfowl and
fieshwater drum eating the zebra mussels. Schloesser et al. (1997) found in a 1993 study
that unionids in the nearshore waters of western Lake Erie were surviving long d e r
unionids in deep water had been completely eradicated by zebra mussels.
They
suggested that zebra mussels voluntarily released fiom unionids in nearshore areas
because of unfavourable habitat conditions, such as waves, water-level fluctuations, and
ice scour. Nichols and Wilcox (1997) and Nichols and Amberg (1999) found zebra
mussels and unionids coexisting (Le. no unionid mortality attributed to zebra mussel
infestation) in Lake Erie wetiands. The theory for this refugium was an interaction
between warm water and soi? sediments; warm water encourageci unionid burrowing, but
soft sediments were required to allow zebra mussel-infested clams to burrow. Schioesser
et al. (1998) found significantly smaller declines in unionid diversity and abundance at
one site surveyed at the outfIow of Lake St. Clair into the Detroit River in a 1992 study,
indicating a potential unionid refügium from zebra mussels.
Unionids had al1 but
disappeared at other survey sites dong the Detroit River. Ail studies that had found
refugia stated that long-term studies would be needed to see if these refigia wodd ensure
unionid survival in zebra mussel-infested waters.
Al1 of these researchers offered
theories as to why unionids were surviving in these areas, but they did not consider the
effects of water currents sufficient to keep zebra musse1 densities Iow enough to d o w
unionids to survive.
Unionids require shallow water, long distances (>1.5 km) from veliger-carrying,
deep-water currents to survive in zebra mussel-infested waters. The highest correlation
between distance of sarnple site from deep-water currents and unionid density per person
hour was at 2 km distance (?=0.554).
Zebra musse1 densities per unionid in the area
around the St. CIair River delta were significantly lower than the nurnber of zebra
mussels per unionid found in studies where unionid mortality was extreme (Gillis and
Mackie 1994, Mackie et ol. 2000, Nalepa et al. 1996, Ricciardi et al. 1995). The unionid
refugium in Metzger Marsh, described in Nichols and Amberg (1999) and Nichols and
Wilcox (1997), is over 2 km fiom waters deepei than 2 m and in an area of low flow,
relatively isolated (from deep-water currents) from the rest of Lake Erie, similar to the
refugia in Lake St. Clair. Other areas in Lake St. Clair with this criterion were predicted
to be near Mitchell's Bay in Ontario and in Anchor Bay and other sites in the St. Clair
River delta on the American side of the lake. Parts of Rondeau Bay and Inner Long Point
Bay on Lake Erie are both long distances from deep-water, veliger-carrying areas.
Althou& the lake current effects on these areas were not investigated, the environments
of these areas closely resemble other unionid refugia and should be s w e y e d to see if
populations remain.
Twenty-seven species of unionids have been found in surveys of Lake St. Clair,
21 of these species survive in a unionid refugium near the S t Clair River delta Other
unionid refugia, such as Metzger Marsh in Lake Erie, may exist in the lower Great Lakes
in similar shallow areas, isolated fkom deep-water currents. The presence of survïving
unionid populations is directly related to wind-driven water current patterns in Lake St.
Clair. The current patterns combined with water depth may keep zebra mussels fiom
reaching densities high enough to eradicate unionid populations around the S t Clair
River delta.
Table 1: Correlations between % thne sites are greater than various distances (arcsine
transformed) and unionid densities in person hours (l/x+l transformed). n=89 sample
Distance firom
,1
1 -toasts of lake
-0.697
-St. Clair delta
>2 k m
>3 km
>3.5 k m
>4 km
>5 km
-toast between Puce and Belle
River (Ontario)
-St, Clair delta
-toast between Puce and Belle
River (Ontario)
-St.CI& delta
-St. CI& delta
-St. Clair delta
-St. Clair delta
-0.744
cO.001
-0.7 18
cO.001
-0.71 1
-0.648
-0.537
<0.001
<O.OOl
<O.OO1
e 1999 Sample Sites
5
O
5
10Kilorneters
Propcbon: U T I K I 7
Figure 1: Map of Lake St. Clair showing major landrnarks, 1999 sampling sites, and
bathymetry.
-
/\/ Selected North w h d driven currents
,lV Unsalectad North wind drîven currents
/V Coastline
5
O
5
h
10 Kilometers N
-
/\/Sslected Northeast wind drken currents
A / Unseleded Northeast wind driven currents
NCoasttine
5
O
5
10Kilameters
Proj*Ftïon: UTU-17
Dstum: W G S - 8 4
~ u n e n t s : Ayers IOCM
HOAA: E c r t g c - a W and E h - p c . i W
~'2~~"''
sourttr:
Currcnts: AYCIS 1-
N O M : E c s t g c . r a ) and Eli'ps.aW
N
Figure 2: Map of Lake St. Clair showïng selected (over water >2 m) and unselected
(over water <2 m) North and Northeast wind dnven currents (adapted fiom Ayers 1964).
,4,/ Selacte d East wind drben currents
fiy'unselected East wind driven currents
Coastline
5
O
5
10Kilometerç
a
/V S e l e d e d Saulheast wind drken currents
O
5
10 Kilometers
D h m : WGS-84
Sources:
Curienis: ~ y e r sIW
H O M : E a t g c . a W and E h - p c . a W
N
,/VUnselected Southeasî wind driven currents
/\/ Coastline
5
Proiectbnr UTM-17
/t
a
N
~'2~~G2~''l7
Sourou:
C u r r e n t : Ayers 1W O U : E c s L p r a m and E l n - p c e m
-
Figure 3: Map of Lake St. Clair showing selected (over water 22 m) and unselected
(over water <2 m) East and Southeast wind driven cments (adapted from Ayers 1964).
-
/\/ Selected South wind d r i e n currents
,/VUnseiected South wind driven currents
/'V Coastline
5
O
5
10 Kilometers
-
Q
Projeothn: UTM-17
Datumz WCS-84
Currcnîs: Ayers
lm
H O M : Eatgc.iOO and Eh-pc.aOO
N
~r2~~,"2~417
~Sele~edSouthvestrindd~vencunents
&'Unselected Southwest wind driv en currents
/',/ Coastline
5
O
5
113 Kilometers
h
Currcntr: Ayers tm4
H O M I E a t g c - r O O and Etin-pc.eOO
hl
Figure 4: Map of Lake St. Clair showing selected (over water >2 m) and unselected
(over water <2 m) South and Southwest wind driven currents (adapted f h m Ayers 1964).
93
-
,/
Selected West wind driven currents
Unselected Wesî wind driven currents
Coastline
&'
5
O
5
A
?O Kilometers N
-
N Selected Nonhwest wind driven currents
/\/ Unselected Northwest wind driven currents
/\/ Coastline
5
O
5
10 Kilometers
h
Prai.ction:
UTM-17
Datum: W G S - 8 4
Sources:
Currents: m e r s 1N OAA: Ecstgc.eW and Eh-pc.aOO
~r2~~~2,"417
C u r r e n t : &fers 1N O M ; E a t g c - e a i and Elin-pc.rO0
N
Figure 5: Map of Lake St. Clair showing selected (over water >2 m) and unselected
(over water <2 m) West and Northwest wind driven currents (adapted nom Ayers 1964).
Wnd direction
Figure 6: Mean percent t h e that the wind blew during ice-fiee rnonths on Lake St.
Clair. Error bars show 1 S.E.
Figure 7: Map of Lake St. Clair showhg unionid density ber person hour) at 1999
sarnpling sites.
Figure 8: Map of Lake St. Clair showing percent time 1999 sampling sites are more than
I km f?om deep-water currents.
time site unaffected by currents
0 0-17-168%
O 17.168- 34.336?4
34.336 51-504Ok
51-504 68.672%
Oh
-
û8.672- 85.84Oh
8athyrnetr-y
O- l m
1-2m
2-3m
- 3-4m
4 - 5m
/'. / 5 6m
,
-
,/\,/
/ P " ,
6 - 7m
w 7 - 8 m
,\,/ Coasüine
5
O
5
10 Kilometers
L\
Projection UTY Zone If
Datum: W O S 8 4
Sourmz
National Oceanic and Atmorpheric Adminkation:
Ecstgc.eO0 and E l i n g c - e 0 0
Figure 9: Map of Lake St. Clair showing percent time 1999 sarnpling sites are more than
2 km 5 o m deep-water currents.
time site unaffected by currents
O 0 - 17-16a0h
17.168 - 34.3360r6
34.336 51-504%
51-504 - 68.672%
Oh
-
-
-
.
-
d
*
5
O
5
Prolection. UTM Zone 17
10 Kilometers
4
Figure IO: Map of Lake St. Clair showîng percent t h e 1999 sampling sites are more
than 3 km fiom deep-water currents.
% tirne site unaffected by currents
O O-17-168%
Q 17.16 8 - 34.336%
34.336 - 51-504OA
51-504 68.672!!
68,672 85-84Oh
Bathymetry
0- l m
1-2131
O
-
2-3m
m
.
3-4m
4 - 5m
/'*\, 1' 5 - 6m
6-7m
/ \ / 7 - 8m
A
,/,
Coasüine
.
,
.
>+
-
5
O
5
10 Kilometers
4
Proledion: Ufll Zona 17
Daturn: W O S 8 4
Çoorœs
National Oceanic and Atmospherk Adminisblion:
Ecstpc.eO0 and Elinm.eO0
Figure 11: Map of Lake St. Clair showing percent t h e 1999 sampling sites are more
than 3 -5 km fiom deep-water currents.
time site unaffected by currents
0- 17.168Oh
17.168 - 34.336?!
34.336- 51-504%
51-504 68.672h
68.672 - 85-84Oh
Bathymetry
0- l m
1 2m
2
- 3m
.
Oh
0
O
-
-
,
,
Y,',\-+',
3-4m
4 - 5m
5 6m
6 - 7rn
7 - 8m
-
A,/
A/
,AdJCoastiine
5
O
5
Prolectfon: UTM Zone 17
Daturn: W0S-04
sources
10 Kilometers
a
National Ocaantc ind Atrnospheric Abminisbaion:
Ecstqc.eOO and Eiingc-000
Figure 12: Map of Lake St. Clair showing percent tirne 1.999 sampling sites are more
than 4 km fiom deep-water currents.
time site unaffected by currents
0 0 - 17-168Oh
S 17.168 - 34.33-!
34.336 51 -504Oh
51-504 - 68.67%
68-672- 85.84%
Bathyrnetry
0- l m
1 - 2rn
O h
-
.
.
2-3m
3-4m
4 - 5m
/?\. ,
' 5 - 6m
6 7m
&'7-8m
&'Coastiine
,
,.
:&'
5
-
O
5
10 Kilometers
w
Proleclion: UTM Zone 17
Daturn: W 0 3-84
saurcar
4
National Oceantc and Atmospherk Adrninistrltian:
Ecstqc.eBO and Elinm.eO0
Figure 13: Map of Lake St. Clair showing percent time 1999 sampling sites are more
than 5 km f?om deep-water currents.
Degree sites affected by currents
O Most affected sites
O
O
Moderately Mected sites
a
Least affected sites
Bathyrnetry
0-lm
1-2m
2 - 3rn
. ., 3 - 4m
4 - 5m
,/r'.,,i'5 - 6m
/2L/ 6 - 7m
N 7 - 8m
A,/ Caastline
,
.
i
-
5
O
5
Proleetion: UTY Zone 17
Dafum: WOS-84
sources
10 Kilometers
4
Naitonal Oceanic and Atmospherk Administration:
E c l g c . e O 0 and Elingc.eO0
Figure 14: Map of Lake St. Clair showing the degree 1999 sampling sites are being
afTected by deep-water currents (created by calculating the mean percent time 1999
sampling sites are more than 1, 2, 3, 3.5, 4, and 5 km fkom deep-water currents). "Most
afFected sitesy7are O - 17.168% time rinaffected, Yeast aected sites" are 68.672 85 -84% tirne unaf5ected by deep-water currents.
Degree histonc sites affected by currentç
O
Most Mected Sites
Moderatdy Affected Sites
Least Affeded Sites
O
0-%.O
O
5
Proleetion
UTY Zone 17
Hlçlanc sample aies:
Pugç:ay e l al. (1985)
10 Krlometers
a
National Oceanic and Atmosherk Adminisiration.
Figure 15: Map of Lake St. Clair showing the degree historïc sampling sites (Pugsley et
uL 1985) are being affectrd by deep-water currents (created by calculating the mean
percent t h e 1999 sampling sites are more than 1, 2, 3, 3.5, 4, and 5 km nom deep-water
currents). 'Most af5ected sitesyyare O - 17.168% time unafFected, 'least afEected sites"
are 68 -672 - 85.84% time unaffected by deep-water currents.
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polymorpha) in the Ohio River. American Malacological Bulletin 14:173-179.
Parmalee, P.W. and A.E. Bogan. 1998. The Freshwater Mussels of Tennessee. The
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Pugsley,C.W., P.D.N. Hebert, G.W. Wood, G. Brotea, and T.W. Obal. 1985. Distribution
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Site #
Position
Date(s) Sampled Search Time Decription of Survey Site
(ph)
LSC-w-43
42'?26,03W,82'3 1.98'W
July 2 1/99
0.5
Sand, Sparse grasses, Moderate
Depth
(m)
3.6
ZM
LSC-WI-44
LSC-WI4 1
July 22/99
June 23/99
LSC-WI-52
June 22/99
LSC-WI-53
July 22199
LSC-WI-54
June 22/99
LSC-WI-55
July 22/99
LSC-WI-56
E3 LSC-w-57
LSC-JB-11
July 22/99
July 22/99
June 29/99
LSC-JB-12
LSC-JB- 13
June 29/99
June 23/99
LSC-JB-2 1
June 30199
LSC-m-22
July 6/99
LSC-GL- 1 1
LSC-GL- 12
July 6/99
July 13/99
LSC-GL- 13
July 6199
LSC-SA-11
Sune 8/99
-
'
Sand, Some Veg, Sparse ZM
Muddy Sand Bottom, Pencil
Weeds, Mean ZM Density:
64.67/m2
Sand Bottom, Pencil Wecds,
Mean ZM Density: 232.01m2
SandIClay, Somc Vcg.
(grassesfweeds), New Islands
Sand Bottom, Pencil Weeds,
Mean ZM Density : 131.67/m2
Sand/Silt, Lots of Vcg., Numcrous
ZM druises, Lots of Dcad
Unionids
Sand, Lots of Veg., Sparse ZM
Sand, Some Veg., Sparse ZM
SiltfClay (very soft), lots of
submerged veg
Muddy Sand
Muddy Bottom, Pencil Weeds
3,9
0.6
0.6
0.75
0.6
1.8
3
3.6
0.6
0.9
0.9
MuddyfSilty Sand, lots of
submerged veg,
SiltKlay (very soft), lots of
submerged veg,
Mud, some vcg
Mud, Lots of Submerged Veg,
VERY MURKY
Mud, some veg
0.6
Mud Bottom, intermittent bottom
0.9
vcg.
0.9
0.9
0.6
0.9
# of Live
Unionids (Ipb)
Site #
Position
Date@)Sampled Search Time Decription of Survey Site
(ph)
Mud Bottom, intermittent bottom
veg,
Mud Bottom, intermittent bottom
veg,
Mud Bottom, intermittent bottom
veg,
Not sarnpled, too close to Marina
Sandrock, Patchy Veg, Lots of
ZM, Lots of dead unionids
Mud, Thick Veg., Lots of ZM
LSC-SA- 12
4299.2 lN, 82"27.88'W
June 8/99
30 quadrats
LSC-SA- 13
42'29.12W, 82"27,92'W
June 8/99
30 quadrats
LSC-SA- 14
4Z029.03W, 82O27,96'W. June 8/99
30 quadrats
LSC-GP-II
LSC-GP- 12
4227.62?4,82O5 1.901W July 27/99
42"27.64N, 82'5 1S2'W July 27/99
O
0.5
LSC-GP- 13
42"27,62'N, 82'50.49'W
July 27/99
0.5
LSC-GP-2 1
42"27,05W, 82'52S9'W
July 28/99
0.75
LSC-GP-22
42?6.74W, 82'5 1.74'W
July 28/99
0.5
SandGraveVRock, Patchy Veg.,
Lots of ZM on rocks, Lots of dead
unionids
MuâISilt, Thick Veg,, Sparse ZM
LSC-GP-23
42?6.76W, 82'50.52'W
July 27/99
0.5
Mud, Thick Veg., Spatse ZM
LSC-GP-3 1
42%56?4, 82O52.0O1W July 28/99
0.75
LSC-GP-32
42"25.78N, 82O51.68'W
July 28/99
OS
Sand, Patchy Veg,, ZM on rocks,
very few dead unionids
SandIGravel, Thick Veg., Sparse
LSC-GP-33
42?25.50N, 82"5O.5O1W
July 28/99
0.25
LSC-GP-4 1
LSC-GP-42
4255.24N, 82O52.8 1'W
42%. 1ON, 82'52,28'W
July 28/99
July 28/99
0.75
0.5
LSC-GP-43
42%. 1OW, 82'5 1.43'W July 28/99
0.25
LSC-PU-Il
42'1 8. 10'N, 82'46.33'W
July 8/98
5 quadrats
LSC-PU- 12
42'19.43'N, 82'46.26'W
July 14/98, July
29/99
5 quadrats, 0.5
w
W
ZM
Mud,Thick Veg., small clusters of
ZM, Lots of dead unionids
Sand, Patchy Veg., ZM on rocks
SiltIMud, Thick Veg,, Sparse ZM
Mud/Clay/Silt, Thick Vtg.,
Sparse ZM, Some buried unionid
sheHs
Sand, sparse veg, some m on
rocks, some dead unis
Muddy Sand-Gravel, No Vtg,
Lots of ZM, Lots of dead unionids
Depth
# of Live
(m)
Unionids (/ph)
Site #
Position
Date(s) Sampled Search Time Decription of Survey Site
(ph)
LSC-PU- 13
42"20.47'N, 82'46.26'W
5 quadrats, 0.5
42'1 8.05'N, 82'45.83'W
July 14/98, July
29/99
July 8/98
42020.0OiN, 82'45.83'W
July 15/98
5 quadrats
42'1 8.OO'N, 82'45.67'W
June 19/98
5 quadrats
42'19.3 1'N, 82'45.52'W
July 15/98, July
29/99
July 15/98, July
29/99
5'quadrats, 0.5
42?20.50'N, 82'45.72'W
5 quadrats
5 quadtats, 0.5
42'17.9SN, 82'45.42'W
June 25/98
5 quadrats
42'19.00'N, 82'45.42'W
July 16/98
5 quadrats
42020.00'N, 82'45.42'W
July 16/98
5 quadrats
42'1 7.95'N, 82'45.08'W
June 26/98
5 quadrats
42'19.23'N, 82'4495'W
July 16/98, Aug 3/99
5 quadrats, 0.25
42"20,50'N, 82'44.95'W
July 16/98, Aug 3/99
5 quadrats, 0.25
42'1 7,8O'N, 82'44.58'W
June 30198
5 quadrats
42'1 9,OO'N, 82'44.58'W
July 17/98
5 quadrats
42"20.00'N, 82'44.58'W
July 17/98
5 quadrats
4î017.80'N, 82'44.47'W
June 30198
5 quadrats
42'19.23'N, 8î044,51'W July 20198, Aug 3/99
5 quadrats, 0.25
Depth
(m)
Mud-Silt, No Veg, Lots of ZM,
Lots of dcad unionids
Sand, sparse veg, some zm on
rocks, some dead unis
mud-vcry murky, No Veg, Lots of
ZM, Lots of dead unionids
Sand, sparse veg, some zm on
rocks, some dead unis
Gravet-Silt, Pseudofeces, No Veg,
Lots of ZM,Lots of dcad unionids
Mud-Silt, No Veg, Lots of ZM,
Lots of dead unionids
Sand, sparse veg, some ni on
rocks, some dead unis
gravel-rock, No Veg, Lots of ZM,
Lots of dead unionids
mud-very murky, No Veg, Lots of
ZM, Lots of dead unionids
Sand, sparse veg, some ni on
rocks, some dead unis
gravel-rock, No Veg, Lots of ZM,
Lob of dead unionids
mud-very murky,No Veg, Lots of
ZM, Lots of dead unionids
Sand, sparse veg, some ni on
rocks, some dead unis
gravel-rock, No Veg, Lots of ZM,
Lots of dead unionids
mud-very mure, No Veg, Lots of
ZM, Lots of dead unionids
Sand, sparse veg, some zm on
rocks, some dead unis
gravel-rock, No Veg, Lots of ZM, 4.5
hts of dead unionids
# of Live
Unionids (/ph)
Site #
*
u;
Position
Date(s)
Sampled
Search Time Decription of Survey Site
5 quadrats
(ph)
LSC-PU-73
4290.50'N, 82'44.5 1'W
LSC-PU-8 1
42'1 7.65'N, 82'44.20'W
July 20198, Aug
3/99
July 1/98
LSC-PU-82
42' 1g.OO'N, 82O44.2O'W
July 2 1/98
5 quadrats
LSC-PU-83
42?!0.00'N,
July 21/98
5 quadrats
LSC-PU-9 1
42'17.5O'N, 8Z043.53'W
July 1/98
5 quadrats
LSC-PU-92
42'18.95'N, 82'43.45'W
5 quadrats, 0.25
LSC-PU-93
42°20.19'N,82043.61'W
LSC-PU-1O 1
42"17.50'N, 82'43.33'W
July 2 1/98, Aug
3/99
July21/98,Aug
3/99
July 2/98
LSC-PU-102
42'19.00'N, 82'43.33'W
July 22/98
5 quadrats
LSC-PU- 103
4Z020.00'N, 82'43.33'W
July 22/98
5 quadrats
82'44.20'W
LSC-MB-11
5 quadrats
5 quadrats, 0.25
5 quadrats
1.5
LSC-MB- 12
42'2 1SO'N, 82?6,77'W
Aug 18/99
0.5
LSC-MB-13
42'2 l.6O'N, 8228.76'W
Aug 18/99
0.5
LSC-MB-2 1
42?2,48'N, 8295.33'W
Aug 12/99
0.75
LSC-ME3 1
4293.5 lYN,8225.54'W
Aug 12/99
0.75
mud-very murky, No Veg, Lots of
ZM, Lots of dead unionids
Sand, sparse veg, some zrn on
rocks, some dead unis
gravel-rock, No Veg, Lots of ZM,
Lots of dead unionids
mud-very murky, Lots of ZM,
Lots of dead unionids, No Veg,
Sand, sparse veg, some ni on
rocks, some dead unis
gravel-rock, No Veg, Lots of ZM,
Lots of dead unionids
mud-very murky, No Veg, Lots of
ZM, Lots of dead unionids
Sand, sparse veg, some zm on
rocks, some dead unis
gravel-rock, No Veg, Lots of ZM,
Lots of dead unionids
mud-very murky, No Veg, Lots of
ZM, Lots of dead unionids
Sand, Some Grass, young of year
n on unis (<2mm), many
deformed unis
Sand, Silt, Clay, No veg, ni on
hard surfaces, young of year n i ,
some unionid shells
Soft claylsilt, No veg, young of
year zm druises, m on dead uni
shells
Smd, Lots of veg., some zm on
veg (amm)
Sand, Lots of veg., some zm on
ven and dead unis (<2rnm)
Deptb
(m)
# of Live
Unionids (/ph)
Site #
Position
Date(@Sampled Search Time Decription of Survey Site
LSC-MB-32
42?23.64'N, 82"25,80'W Aug 13/99
LSC-MB-33
LSC-MB-4 1
42"23.49'N,82°27.15'W
4254,69'N, 82'25.76'W
(ph)
0.75
Aug17199
Aug 13/99
Sand, some veg, few n on veg
(<hm),some dead unis
Clay, thick veg, few ni
Sand, lots of veg, few ni on veg
and dead unis (<2mm),lots of
dead unis near grasses, some dead
Corbicula
LSC-MB-42
4224,49'N, 82'27.47'W
AU^ 17/99
Silt, Sand, Clay, thick veg, few
ni,No dead uni shclls
c.
C
LSC-MB-5 1
42"25.53'N, 82'26.18'W
Aug 13/99
LSC-MB-52
42'25.41 'N, 82'27.33'W
AU^ 17/99
BR-1 1
42O15.08'N, 82'42.83'W
May 19199
BR- 12
42'16,46'N, 82'42.88'W
June 1/99
RR-Il
42'1 5.08'N, 82'37.17'W
June 1/99
al
LSC-WI = Lake St. Clair near Walpole Island 1,R. and the St. Clair River Delta
LSC-JB = Johnston Bay in the St. Clair River Delta
LSC-GL = Goose Lake in the St. Clair River Delta
LSC-SA = Lake St. Clair near St. Anne Island in Walpole Island I.R.
LSC-GP = Lake St, Clair near Grosse Pointe, .MI
LSC-PU = Lake St. Clair between Puce and Belle River, ON
LSC-MB- Lake St. Clair between Mitchell's Bay and Thames River mouth
BR = Belle River, ON
RR = Ruscom River, ON
Sand, lots of short veg, few ni on
veg and dead unis (<2mm),some
dead unis
Clay, very thick veg, lots of dead
ni (live on plants), No dead uni
shells
Belle River @ 12-13 Side Rd.
Bridge, Mud, slow moving
Belle River @ Reg, Rd. 42
Bridge, Mud/Gravel, slow
moving, Deep diRcult to sarnple
Ruscom River @ Rochester Twp,
Con 6, Mud, dowstream of sheep
f m . mod current
Depth
(m)
# of Live
Unionids (/ph)
0.75
O
Appendu 2: Matrix of morphological, reproductive, and ecological traits used in Distriminant Function Analyses.
Species
C
+
4
A ctinonaias ligamentina
Am Mema plicata
Anodontoides ferussacianus
Elliptlo dilatata
Epioblasnta torulosa rangiana
Ftrsconaiaflava
Lampsilisfmciola
Larnpsilàs curdium
Lampsilis siliquiodea
Lasmigona cornplanata
Larmigona costata
Leptodeafiagilis
Ligumia nasuta
Ligumia recta
Obliquaria reflera
Obavaria subrotunda
Pleurobema sintoxia
Potamilus alaius
Ptychobranchtrsfasciolaris
Pyganodon grandis
@adritla pusiulosa
Quaàrula quadrula
Simpsonaias ambigua
Strophiîus undulatus
Truncilla donaciformis
Truncilla truncata
Villosa iris
Shell
Maximum
Morphology Shell Length
(hW
(mm)
1 .50
75.00
Maximum
Shel'
Height
(mm)
45.00
Maximum
Maximum
Shell
Shell Width Thiekness
(mm)
(mm\
30.00
4.00
Number of Nurnber of Known Combiord Fish Host
Months
Fish Hosts
Abundance in LStC.
Cravid
10.00
9.00
10.23
Appendix 3: Maîrix of morphological, reproductive, and ecological traits used in Distriminant Function Analyses of unionid
conservation rankings.
Species
Actinonaias ligamentina
Alasmidonta marginafa
Alasmidonta viridis
Am blema pllcata
Andontoides ferussacianus
Cyclonoius tubercula
EIliptio dilatata
l$loblasma tondosa rangiana
@loblasma triqiretra
Fusconalajhva
hmpsilis fasciofa
Lampsilis cardium
Lampsilis siliquiodea
Lasmigona complanata
Lasmigona compressa
Lasmigona costatu
Leptodcafiagilis
Ligumia nasuta
Ligtrmia recta
Obliquaria refïexa
Obovaria subroturyia
Pleurobema sintoxia
Potamllus alatus
P~ychobranchus
fàsciolaris
Pyganodon grundis
Quadrulapushclosa
Quadrula quadrula
Simpsonaias ambfgua
Strophihr~undulatus
Toxolasmapwvus
TmmiIIa donacrform
Truncilla truncata
Utterbackia imbecillus
Villosafabalis
Villosa Iris
Ontario
She"
Conservation
Rankings
Morphology
(MW)
2.0
1.23
Maximum ShellMaximum ShellMaximurn Shell
Maximum
Thiekaess
Length (mm) Height (mm) Width (mm)
150.00
80.00
65.00
Number of Months
(mm)
Gravid
10.00
10.00