AMER. ZOOL., 36:239-243 (1996)
Introduction: The Biology, Ecology, and Physiology of Zebra Mussels1
JEFFREY L. RAM
Department of Physiology, Wayne State University, Detroit, Michigan 48201
AND
ROBERT F. MCMAHON
Center for Biological Macrofouling Research, Department of Biology, Box 19498,
The University of Texas at Arlington, Arlington, Texas 76019
The papers in this issue of American Zoologist were originally presented in a symposium entitled, "The Biology, Ecology,
and Physiology of Zebra Mussels," held 5
January 1995, at the American Society of
Zoologists (ASZ) Annual Meeting in St.
Louis, Missouri. The zebra mussel (Dreissena polymorpha), is an endemic, freshwater, European bivalve mollusc accidentally introduced into the North American
Great Lakes. Introduction was most likely
by release of larvae with ship ballast water
into Lake St. Clair, near Detroit, Michigan
in 1986 (Hebert et al., 1989).
The zebra mussel's high fecundity, passively dispersed planktonic veliger larval
stage, and ability to attach by proteinaceous
byssal threads to boat and barge hulls, nets,
buoys, and floating debris allowed it to
spread rapidly throughout the lower Great
Lakes and freshwater portions of the St.
Lawrence River after its initial introduction
(Fig. 1). It subsequently dispersed east
through the Erie Canal, into the Hudson
River, overland (by unintentional human
mediated vectors) into the upper Susquehana River in New York, and south and
west through the Illinois River into the Mississippi River near St. Louis. After entering
the Mississippi River, the zebra mussel rapidly spread downstream to New Orleans,
LA, and upstream to La Crosse, WI. It is
now found in the lower portions of most
major Mississippi River tributaries, including the Ohio, Tennessee, Cumberland, and
1
From the Symposium Biology, Ecology and Physiology of Zebra Mussels presented at the Annual Meeting of the American Society of Zoologists, 4—8 January 1995, at St. Louis, Missouri.
Arkansas Rivers, but not the Missouri River
(Griffiths et al, 1991; Ram et al, 1992;
McMahon, 1992; O'Neill and Dextrase,
1994) (Fig. 1). By the end of 1995, the zebra mussel had invaded waters in 20 of the
38 U.S. states east of the Rocky Mountains
and the Canadian provinces of Ontario and
Quebec (Fig. 1). By 1994, it was also beginning to disperse, apparently by human
mediated vectors, into smaller, inland bodies of water. As of January 1996, sightings
of zebra mussels have been confirmed in 54
isolated inland lakes in Illinois, Indiana,
Michigan, New York, Ohio, Vermont and
Wisconsin (United States National Biological Service, 1995a). A second species of
freshwater, dreissenid mussel, the quagga
mussel, Dreissena bugensis, has also been
introduced into the Great Lakes. Initially recorded in Lake Ontario, it is spreading rapidly and now occupies the eastern basin and
southern shore of Lake Erie, the southern
shore of Lake Ontario and the freshwater
portions of the St. Lawrence River (May
and Marsden, 1992; Mills et al., 1993,
1996; Zebra Mussel Information Clearinghouse, 1995).
The tendency of zebra mussels to form
dense aggregates on hard surfaces causes
them to have great economic impact. Its
planktonic veliger larvae and translocating
juveniles are entrained on intake water into
man-made raw water systems where they
settle and attach in large numbers. Newly
settled mussels reach such high densities
(up to 700,000 irr 2 , Griffiths et al., 1991)
and have such rapid post-settlement growth
rates (Nichols et al., 1990, 1996) that they
rapidly form thick mats, occluding or
blocking flow even in large diameter piping
239
240
J. L. RAM AND R. F. MCMAHON
FIG. 1. Map showing the distribution of the zebra
mussel, Dreissena polymorpha in North America as of
October, 1995. Dotted lines show the borders of U.S.
states and Canadian provinces and solid lines indicate
major rivers and lakes. Solid circles are confirmed reports of individual zebra mussel populations while
darkened areas indicate regions were mussel populations have become contiguous (data from United States
National Biological Service, 1995b).
(Mackie et al., 1989; McMahon, 1992; Kovalak et al., 1993; Jenner and JanssenMommen, 1993). Early North American
experience with mussel infestations in the
raw water systems of power stations, potable water treatment plants and industrial facilities on the Great Lakes suggested that
their fouling developed more rapidly and
was more severe than reported in Europe
(Griffiths et al., 1989; LePage, 1993; Claudi
and Mackie 1993). Thus, the zebra mussel
invasion of North America will lead to increased macrofouling impacts, the eventual
costs for repair, replacement and control estimated to be several billion dollars annually (Roberts, 1990; Office of Technology Assessment, United States Congress,
1993).
The zebra mussel is also negatively impacting native North American freshwater
biota. Extensive mortality or even complete
extirpation of native North American
unionid bivalve populations has been reported in habitats densely colonized by ze-
bra mussels. The mussels settle on the posterior portions of unionid shells extending
above the substratum surface. Massive infestations cause unionids to be dislodged
from the substratum and/or experience starvation as zebra mussels filter seston food
from the unionid's inhalant flow (Mackie,
1993; Schloesser et al., 1996). Suspensionfeeding by dense zebra mussel populations
may also result in density reductions of
phytoplankton and suspended inorganic
matter (Maclsaac et al., 1992). The resulting increase in water clarity can lead to increases in the density and biomass of benthic macrophytes and animals (Hebert et
al., 1991). Such diversion of energy flow
by zebra mussels from pelagic into benthic
food chains has been hypothesized to negatively impact pelagic fish populations
while increasing demersal fish productivity
(Karnaukhov and Karnaukhov, 1993). Zebra mussels also accumulate environmental
contaminants; thus, predators feeding on
zebra mussels can have notably elevated
tissue contaminant loads and reduced reproductive success (see Maclsaac et al., 1996).
Zebra mussels have already caused considerable ecological change in the lower Great
Lakes and their ecological impacts are likely to extend into other drainage systems as
they disperse throughout North America.
While Dreissena polymorpha is likely to
have negative environmental and economical impacts on North American freshwaters,
North American investigators have found
that this species can also be a model organism for biological, ecological and physiological investigations. The mussels are easy
to collect, maintain, and culture (Nichols,
this volume) making them adaptable to a
wide variety of laboratory investigations,
and, because they are epifaunal and sessile,
they also make excellent subjects for field
ecological or environmental studies. For example, the information base on zebra mussel physiology has been greatly increased
by recent North American studies of ion
transport (Horohov et al., 1992; Dietz et al.,
1996), ciliary function (Silverman et al.,
1996), physiological resistance and capacity
adaptations (McMahon, et al., 1993 and
McMahon, 1996), and reproductive/
developmental mechanisms (Ram et al.,
241
INTRODUCTION
1993; Fong et al., 1993, 1994; Miller et al.,
1994; Ram et al., 1996).
Although much information has been accumulated through European studies, the
zebra mussel's invasion of North America
has triggered a rather extensive American/Canadian research response, sponsored
by many agencies, including NSF, NOAA,
the U.S. Army Corps of Engineers, the U.S.
National Biological Service, power and water utilities, and Canadian and Ontario governmental research and environmental
agencies. As North American data have accumulated, it has become apparent that
North American and European zebra mussels are not equivalent in all aspects of their
biology, ecology and physiology (Mackie
and Schloesser, 1996; McMahon, 1996).
Lack of congruence between European and
North American data may partly result from
the rapid dispersal of North American zebra
mussels, their elevated growth rates and
lack of natural predators, and the fact that
the probable source of North American
mussels was the Black Sea region of the
Ukraine at the extreme southern portion of
the zebra mussel's European range. 'Zebra.
mussels from this area have been little studied. Instead, the majority of European studies have concentrated on northern European
mussels drawn from much colder waters.
Thus, North American zebra mussels appear to be more thermally tolerant (McMahon et al., 1993), to have greater growth
rates (Griffiths et al., 1991) and to display
greater reproductive variation (Garton and
Haag, 1993) than reported for mussels from
northern Europe. In addition, genetic and
morphological studies on North American
quagga mussels prove decisively that they
are genetically distinct from zebra mussels
and that their source populations are in the
Dneiper River/Black Sea Region of Ukraine
(Spidle et al, 1994; Rosenberg and Ludyanskiy, 1994; Marsden et al., 1996).
consin Sea Grant Institute, 1994; Ontario
Hydro, 1995), these volumes have focused
primarily on this species' macrofouling impacts and control, have been largely reports
of nonzoologists, have not attempted to analyze, review, or integrate information from
multiple sources, and have not been available to the general zoological research community. A more biologically oriented treatise on zebra mussels is Zebra Mussels: Biology, Impacts and Control, edited by Nalepa and Schloesser (1993), which is a
collection of papers on aspects of the mussel's biology and macrofouling control.
However, much of the research reported in
this volume was carried out prior to 1991,
before zebra mussels had dispersed little beyond Lake Erie and when most North
American investigators had studied them
for less than one year. Intensive study of
zebra mussel biology in North America has
occurred over the four years subsequent to
publication of this treatise (Nalepa and
Schoesser, 1993). The symposium papers in
this issue of American Zoologist update the
biology, ecology, and physiology of zebra
mussels in North America and provide a
comparison with European findings. As zebra mussels become available to an increasing number of North American investigators, this publication will provide a new and
comprehensive data base supporting further
research on this ecologically and economically important species.
ACKNOWLEDGMENTS
This symposium was sponsored by the
Division of Invertebrate Zoology and cosponsored by the Division of Comparative
Physiology and Biochemistry and the Division of Ecology of the American Society
of Zoologists. We are grateful to the symposium participants who devoted considerable time and effort to preparing both their
symposium presentations and papers. Many
The chapters in this symposium provide of the participants allocated personal or
a new synthesis and integration of recent grant funds to partially support their travel
biological studies on North American vari- expenses to the symposium. We would also
eties of dreissenid mussels. Although full like to acknowledge the experts who relength papers have appeared in the pub- viewed the papers presented in this volume.
lished proceedings of several annual con- Cornelia Schlenk, Assistant Director, New
ferences on zebra mussels and other exotic York Sea Grant Institute, and Charles R.
species {e.g., Tsou and Mussalli, 1993; Wis- O'Neill, of the "Zebra Mussel Information
242
J. L. RAM AND R. F. MCMAHON
Clearing House of the New York Sea Grant
Institute provided invaluable assistance and
advice regarding seeking of funding for
presentation and publication of the symposium. Presentation and publication of the
symposium was supported by grants from
New York Sea Grant Institute, The Zebra
Mussel Information Clearing House of the
New York Sea Grant Institute and NSF
Grant No. IBN-9416907.
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