&EPA
United States
Environmental Protection
Agency
Office of Research and
Development
Washington DC 20460
EPA/600/3-91/003
February 1991
Ecology and DEC 51994
Management of the
Zebra Mussel and other
Introduced Aquatic
Nuisance Species
-------
EPV600/3-91/003
February 1991
Ecology and Management of the Zebra Mussel and other Introduced Aquatic
Nuisance Species
A Report Based on Presentations and Discussions
at the
EPA Workshop on Zebra Mussels
and other Introduced Aquatic Nuisance Species
Saginaw Valley State University
Saginaw, Michigan, USA
September 26-28, 1990
Edited by
J. David Yount
US Environmental Protection Agency
Environmental Research Laboratory, Duluth, Minnesota
Prepared with the assistance of
ESSA Environmental and Social Systems Analysts Ltd.
and
AScI Corporation
December, 1990
$f) Printed on Recycled Paper
-------
Notice
This document has been reviewed in accordance with U.S. Environmental
Protection Agency policy and approved for publication. Mention of trade names or
commercial products does not constitute endorsement or recommendation for use.
Recommendations and opinions expressed herein do not necessarily represent the
position of the U.S. Environmental Protection Agency.
-------
Acknowledgements
We thank all the participants of the workshop. Their creativity and insights
contribute greatly the success of the project. We are especially grateful to our
overseas participants who brought a new perspective - H. Smit, P. Maitland, V.N
Karnaukhov, N.F. Smirnova, and G.A. Vinogradov. Special thanks are extended to
Chris Wedeles, Carol Murray, Mike Rose, and Pille Bunnell of ESSA, Ltd. for facilitating
the workshop breakout groups and plenary sessions, and to Pille Bunnell for
organizing the workgroup reports. Gail Irving of ASCI, Duluth, coordinated workshop
logistics. We are grateful to Congressman John D. Dingell's office for providing
translated manuscripts from the Soviet participants.
in
-------
Table of Contents
Page
1. Introduction and Summary 1
Background 1
Earlier Initiatives on Introduced Species 2
Events Following Workshop 3
Workshop Objectives 4
Workshop Process 5
Recommendations 5
2. Ecological Effects of the Zebra Mussel 10
2.1 Issues 10
2.2 Hypotheses of Effect 11
Food Related Effects 12
Habitat Effects 16
Pathogens, Parasites and Toxins 22
3. Rate and Extent of Spread of the Zebra Mussel 25
3.1 Habitat Constraints 25
3.2 Population Growth and Spread within a Lake 28
3.3 Extent of Spread 29
3.4 Rate of Spread from Lake to Lake 29
4. Control of Established Species 30
4.1 Population Control of Established Species 31
Changes to Habitat 31
Biological Control 31
4.2 Control of Problems Caused by Zebra Mussel 32
Problems caused by the zebra mussel 32
Actions available to control the zebra mussel 33
Suitability of Actions to Problem Types 33
4.3 Framework for Evaluating Local Control Actions 34
Sample Applications of Framework 35
5. Prevention of New Introductions 39
5.1 Vectors 40
5.2 Management Alternatives 41
Ships 41
Canals 41
Recreation 42
Accidental 42
Deliberate 43
IV
-------
Page
5.3 Evaluation of Management Options 44
Closing Boat Access to and from Great Lakes 44
Inspections of Ship Hulls, Ballast, and Cargo 44
Treatment of Hull, Cargo, and Ballast 44
Evaluation Criteria 45
Appendices
A. Schedule and Abstracts of Papers, Public Session, Sept. 26, 1990
B. List of Participants
-------
1. Introduction and Summary
This report presents the content of presentations and discussions held over 2
1/2 days in a plenary session and in working groups at the Environmental Protection
Agency's Introduced Species Workshop held in Saginaw, Michigan on Sept 26 - 28,
1990. The purpose of the workshop was to review and evaluate existing information
on the ecology and management of introduced aquatic nuisance species, with a
particular emphasis on the zebra mussel (Dreissena polymorpha), and make
recommendations on how to extend our knowledge and understanding in critical
areas.
The first day of the workshop consisted of a public session. In this session, a
series of formal presentations were made by invited experts on the biology and
ecology of introduced species, and on their sources, prevention and management.
Speakers were asked to provide extended abstracts of their presentations, which are
included here in Appendix A. Two of the speakers, from the Soviet Union, submitted
their entire manuscripts. Rather than attempt to abstract these manuscripts, they are
included, with minor editing, as submitted.
The following 1 1/2 days were devoted to discussions among invited
participants. Although the range of expertise available to the workshop discussions
was extensive, it was not exhaustive, and the time was not long enough to allow for
detailed discussions of scientific, technical, or institutional knowledge. Therefore the
report should be read as an overview of current knowledge and concerns. More
importantly, the assembled wisdom of the workshop participants generated insights
and recommendations with respect to research needs, management options,
information coordination, and potential policy and legislation. The discussions from
each working group are presented in the relevant sections. Recommendations are
presented in the introductory section.
Background
Zebra mussels (Dreissena polymorpha) are a new invading species in North
America with such an enormous feeding and reproductive capacity that they are
spreading in epidemic fashion throughout the Great Lakes. In some areas of the
Great Lakes, they have been reported to reach population densities of greater than
30,000 individuals/m2 and will likely spread to other freshwater systems. Although the
mussels are of immediate economic concern because they clog water intake pipes,
the greatest concern is the possibility of catastrophic changes in the ecology of the
Great Lakes. It has been estimated that the zebra mussels currently filter all the water
in Lake St. Clair several times a day, dramatically shunting the energy flow in the
aquatic food web away from fish. Zebra mussels can strongly outcompete other
indigenous benthic organisms in many temperate aquatic habitats. The success of
1
-------
this mussel will have severe and dramatic consequences on the ecological integrity of
surface waters due to major shifts in trophic interactions the movement of nutrients
and toxic materials, and competition with native species.
The Environmental Protection Agency responded to the zebra mussel crisis by
sponsoring this workshop of experts from the Soviet Union, Europe, Canada, and the
United States to discuss approaches to prevention, control, and potential
environmental impacts of invading species, particularly the zebra mussel. It was
attended by scientists representing government research laboratories, academic
institutions, state and federal regulatory agencies, and shipping and water supply
organizations.
The important issue of determining institutional responsibilities for carrying out
these recommendations was not on the agenda for this workshop, and in any case
was not within the authority of most participants to define. Since this workshop the
U.S. Congress has passed and the President has signed into law, the "Nonindigenous
Aquatic Nuisance Prevention and Control Act of 1990", (PL 101-646) which, among
other actions, defines federal agency responsibilities. This Act will be discussed briefly
below.
Earlier Initiatives on Introduced Species
The need for an overview of available knowledge and an integrated research
plan for the zebra mussel is obvious, and several agencies have taken an initiative in
this direction. Some of the 1990 initiatives which were referred to by participants at
the workshop include:
February: Department of Zoology, University of Guelph conference identifying
current, proposed, and required research on the zebra mussel.
April: Great Lakes Research Consortium and New York Sea Grant workshop to
develop research and data needs on the ecological impacts of zebra
mussels in New York waters.
June: First (organizational) meeting of the United States Great Lakes Non-
Indigenous Species Coordination Committee.
July: Michigan Department of Natural Resources Office of the Great Lakes
compilation of zebra mussel research on the Great Lakes.
August: United States Great Lakes Non-Indigenous Species Coordination
Committee definition of areas of research for a coordinated research
program.
-------
August: U.S. Environmental Protection Agency Great Lakes National Program
Office organized a series of conference calls to develop an assessment
paper on exotic species, with emphasis on the zebra mussel.
The September workshop hosted by EPA was intended primarily to inform state
and federal regulatory and national resource management agencies who are charged
with implementing existing legislation. The workshop considered a broad spectrum of
issues and users, and brought in European and Soviet scientists who had not
previously been consulted. It was not intended to be definitive, but rather to be a
substantial step towards developing a clearly defined strategy based on both
scientifically and practically defined needs.
Events following Workshop
In October the United States Congress passed the "Non-indigenous Aquatic
Nuisance Prevention and Control Act of 1990" (P.L 101-646). The purposes of this
Act are "(1) to prevent unintentional introduction and dispersal of non-indigenous
species into waters of the United States through ballast water management and other
requirements; (2) to coordinate federally conducted, funded or authorized research,
prevention, control, information dissemination and other activities regarding the zebra
mussel and other aquatic nuisance species; (3) to develop and carry out
environmentally sound control methods to prevent, monitor and control unintentional
introductions of non-indigenous species from pathways other than ballast water
exchange; (4) to understand and minimize economic and ecological impacts of non-
indigenous aquatic nuisance species that become established, including the zebra
mussel; and (5) to establish a program of research and technology development and
assistance to states in the management and removal of zebra mussels." By this Act
many of the recommendations made in this report have become law.
The Act directs the Secretary of the Department of Transportation (through the
U.S. Coast Guard) to issue voluntary guidelines within 6 months to "prevent the
introduction and spread at aquatic nuisance species into the Great Lakes through the
exchange of ballast water of vessels prior to entering those waters." Within 24 months
the Secretary of Transportation, in consultation with the "Task Force", is directed to
issue regulations for the above purpose.
The Task Force, co-chaired by the Director of the U.S. Fish and Wildlife Service
and the Secretary of Commerce for Oceans and Atmosphere, consists also of the
Administrator of the U.S. EPA, the Commandant of the U.S. Coast Guard, the
Assistant Secretary of the Army (Civil Works), and the heads of any other federal
agencies deemed appropriate by the chairpersons. The Task Force members (or their
official representatives) are charged with implementing most of the provisions of the
Act. These include development of an aquatic nuisance species program;
development of Great Lakes regional coordination; and review of policy on intentional
-------
introductions. In addition, some of the Task Force members have broad authorization
in areas related to introduced species. The U.S. EPA, for example, is charged with
conducting basic ecological research on factors that affect the well-being of
ecosystems, and on indicators of ecosystem health.
The U.S. Great Lakes Non-Indigenous Species Coordination Committee,
referred to above, met again in early December to develop a coordinated research
plan. At this meeting members voted to include U.S. industrial organizations who are
funding zebra mussel research, and to invite participation by appropriate Canadian
groups.
Workshop Objectives
The formal objectives of the workshop were to:
1. Identify the information gaps in our knowledge of zebra mussels and
other introduced aquatic species that inhibit our ability to make
management decisions;
2. Identify the research needs to fill the information gaps;
3. Identify advantages and disadvantages of management alternatives; and
4. Prepare recommendations for managing introduced species and
nrpv/pntinn fi iti irp invacinnQ
preventing future invasions.
From the outset it was recognized that the short workshop would not be able to
produce all the answers. However, it is also recognized that this workshop is an early
step in a much larger process to develop a coordinated program of research and
management of non-indigenous species in the Great Lakes.
-------
Workshop Process
In order to accomplish as much as possible during the day and a half available
for the workshop, most of the time was spent in working groups. Four working
groups were defined.
Prediction
1.
3.
Predicting the rate and extent of
spread.
Predicting Ecological effects
Control
2. Prevention of new introductions
4. Control of established species
Because of limited time, the scope of discussion in three of the groups was
limited to zebra mussels. However, the group discussing the prevention of new
introductions clearly emphasized introductions in general, since the zebra mussel is
already present. All discussions primarily focussed on the Great Lakes Basin, adding
more localized or continent-wide consideration where appropriate. Each of the
following chapters summarizes the discussions from one of the working groups.
Summary of Recommendations
Each of the four working groups developed a set of recommendations which
ranged from specific research needs to overall coordination of the issues related to
introduced species. Although the combined list appears long, and in implementing the
recommendations one would have to consider the details, it is possible to extract a
few basic themes that help to synthesize and summarize the recommendations.
The need for an information clearing house, database, or series of databases
became apparent - the short time that we have had to deal with the zebra mussel and
the urgency of the problems have led to a burst of research and management effort
which would be far more effective if it were well coordinated. Similarly, a commission
to help coordinate the effort on an international scale is highly desirable.
A number of specific activities are recommended to ensure that the information
in the database(s) is current and credible. These include the translation of the
European and Soviet literature, monitoring programs, and the review and evaluation of
control methods. Modelling is proposed as a method to help guide research, predict
spread, evaluate control methods, and manage activities. Some management
activities are singled out as particularly timely; namely, clarification of permitting
procedures for control methods, development of a ballast water management plan,
and the implementation of a public information system aimed at reduction of spread,
-------
effectiveness of management, and public support for the required research. Research
designed to provide critical basic information is highlighted as a basic
recommendation.
The next step is to provide a forum which will allow the people concerned to
prioritize recommendations and to propose appropriate action and develop a strategy
for its implementation. The research and management community are willing; what is
needed is the institutional support necessary to fund, coordinate, and implement a set
of integrated programs.
Ecological Research Needs and Recommendations
For most of the ideas described below, there is an explicit need for studies on
the basic biology and autecology of zebra mussels. To understand the ecological
effects that zebra mussels cause we need basic information such as:
genetic characteristics of populations;
chemical and physical requirements;
parasites of zebra mussels;
behavior and spatial distribution of different life stages;
preferred prey species;
preferred prey sizes;
rates of uptake of contaminants.
Zebra mussels will impose dramatic effects upon the aquatic ecosystems in
which they become established. The following list summarizes the possible effects of
zebra mussels which should be addressed through research:
1) effects of water clarity caused by predation on phytoplankton and detritus;
2) effects on aquatic food webs and fish community structure including:
effects on higher trophic levels of competition for food;
effects of concentrating biomass in the benthic layer;
effects of use by higher trophic levels of zebra mussel veligers and
adults as prey;
effects of temporal "pulse" of zebra mussel veligers both as predators
and prey; and
effects of changes in benthic and planktonic bioenergetics
-------
3) effects on nesting and spawning habitats of native fish species as a result
of competition for space;
4) effects on native clam species with special regard to rare and endangered
species;
5) effects on distribution of toxics in the aquatic community; and
6) effects as vectors of disease and parasites.
Recommendations for Predicting Rate and Extent of Spread
The prediction of the rate and extent of spread of zebra mussels is a
complicated and difficult issue given the resilience and adaptability of the organism.
Mapping exercises using a Geographic Information System would provide useful tools
to document where zebra mussels are found now and where they are likely to move
given the availability of adequate habitat. In order to make credible predictions the GIS
analysis must be recalibrated and updated as new information becomes available.
Throughout the course of discussion the group listed several recommendations
to increase our understanding of zebra mussel dynamics. These included:
1) Define threshold limits for zebra mussel habitat suitability for North
America. Replace European information with more relevant data from the
North American experience. This increase in knowledge of habitat
constraints would be used to calibrate population growth models and to
predict the potential distribution of the mussels.
2) Document present zebra mussel locations and estimate population
stability using a population growth modelling approach.
3) Define future distribution of zebra mussels in North America. This would
be accomplished through a GIS analysis.
4) Develop a central depository of zebra mussel literature to facilitate
information availability and provide a list of on-going zebra mussel
research projects citing researcher and location.
5) Assign an "International commission to coordinate the proposed GIS
work.
6) Increase public education to inform citizens of what zebra mussels are,
what they do, how they do it and what ordinary citizens can do to control
them.
-------
Recommendations for Control of Established Species
1. Monitor existing zebra mussel population levels in infested lakes. Since
there is some indication that the natural course of the invading zebra
mussel population is to decline, we should continue to monitor existing
populations. Similarly, we should identify any biological control agent
that is in place or increasing, whether it be native or inadvertently
introduced.
2. Begin a review of potential biological control methods. Although there is
a reluctance to expose ourselves to the risks inherent in introducing new
organisms to an ecosystem, it would certainly be useful to have a better
understanding of long-term control options. Since research to identify
and possibly modify a predator, parasite or disease-based control is time
consuming, this should begin at once.
3. Implement a review of all control actions. In order to appropriately review
all the control actions that can be used to manage problems caused by
zebra mussels the appropriate expertise will be required for each type of
problem and each type of action. Working groups could be formed to
review suitable groups of actions. The purpose of the review would be
not only to evaluate suitability and acceptability of the actions, but to
synthesize the knowledge so that it can be included in a database and
accessed by a clearing house. The review can be structured to identify
uncertainties and to prioritize research requirements. Mathematical
modelling of the effectiveness and of the potential ecological and social
impacts of control actions is recommended as an evaluation tool.
Generic models could be developed, which could then be fitted to
various facilities through use of appropriate parameters and/or modules.
4. Initiate a process to review and evaluate chemicals for environmental and
health effects. This recommendation advocates that chemical treatment
methods be evaluated first. Many chemicals are already in use, and
have not been fully evaluated. Therefore, a suitable review process is
needed immediately. The review will require use of ecological and
medical expertise, and there will be institutional and regulatory
implications to the permitting procedures.
5. Develop an information base of zebra mussel control methods. This is a
variant of the recommendation for an information clearing house, and is
conceived Jo be part of a larger introduced species clearing
house/information system. Although an informal information network
currently exists among the major industries affected, this network will
inevitably become less efficient as the extent of the problem grows, and
new inquiries will not have ready access. There is a need for ready
access to the details pertinent to the application of control actions,
particularly those related to impacts and effectiveness. The information
base would include the results of the expert review, and would be
designed to enable easy updating.
8
-------
6. Enlist engineers to investigate design solutions and physical control
methods. Long-term environmentally benign solutions are most likely to
be based on design innovations. Although engineers are probably
working on this within major industries, a broader encouragement of this
direction may be socially desirable. Inclusion of engineers in the control
method review process will encourage exchange of information among
industries and disciplines, and may result in specific initiatives which
could be funded through a mixture a sources.
Recommendations for Preventing New Introductions
Ships, specifically ballast water, were identified as the most important as well as
the most manageable anthropogenic vector for the introduction of new species, and
much discussion focused on management actions targeting this vector. Major gaps
were recognized in our current knowledge of ballast water treatment methods. As a
result, research requirements were identified concerning possible treatment methods
(e.g., ozone, heat, ultra violet light, chemicals, ultrasound, electric current, filtering).
The research should include the relative effectiveness of various methods, and their
feasibility from an engineering point of view.
Although this workshop did not address the problems of mixing gene pools
within species, this issue should be considered in future discussions.
Six recommendations are offered toward preventing the introduction of new species:
1. Implement a ballast water management plan for ships entering the Great
Lakes Basin. This plan would adopt a variety of techniques and options
targeting the ballast vector. Under the Management Plan incoming ships
would be required to provide the coordinates locating where the ballast
water was exchanged and to cite the amount of ballast exchanged.
Otherwise, incoming ships would be required to provide information on
the origin of their ballast water (which may include multiple sources).
2. Evaluate ballast water treatment methods. Once research has been
conducted, each treatment should be evaluated (environmental,
economic, social - including health and safety - and political) to identify
the optimum method(s).
3. Initiate widespread education programs immediately to: a) inform the
general public as well as those responsible for the various vectors about
the seriousness of the issue, their potential unwitting contribution to the
problem, and the role they may play in the prevention of new
introductions, b) encourage research within institutions and industries by
advertising a need for information and technology, and c) inform
regulating bodies about initiatives in other jurisdictions. The media, as
well as non-governmental organizations could play a role, with the
Canadian and United States governments taking the lead in initiating
programs and ensuring that the information is accurate and appropriate.
-------
4. Strive for communities with increased resistance to invasion. Since
disturbed communities are more susceptible to the establishment of
invading exotic species, any environmental policy or strategy in the
United States should be designed to encourage healthy natural
communities. This might require the evaluation of "legally-sanctioned"
introductions (e.g., aquaculture, planned introductions for biological
control, industry or sport) that were not included in our discussions.
5. The goal of any prevention program should be no introduction of new
species. Although this goal may be impossible to achieve, aiming for
less increases the rate of failure.
6. Establish an information clearing house to deal with the many aspects of
exotic species presence. This would include environmental effects, the
rate and extent of spread, the control of established populations or the
prevention of new introductions and would ensure information transfer
between governments, industries, research institutions and countries.
The clearing house role woujd be to maintain and update a database of
the existing information and its location.
Invading exotic species, and their environmental and subsequent economic
effects, is a serious issue. The zebra mussel in the Great Lakes may provide a real-life
worst-case-scenario. While dealing with the zebra mussel problem, approaches should
not be limited to a single species but should also consider communities or whole
ecosystems. The successful prevention of new introductions will likely require
interdisciplinary global effort.
2. Ecological Effects of the Zebra Mussel
At the workshop no attempt was made to prepare a comprehensive review of
the ecological effects, but rather to provide an overview of processes and pathways
that may be affected by zebra mussels. This was accomplished by constructing
simple conceptual models or hypotheses of effect (sometimes referred to as impact
hypotheses) that specify the chain of events through which effects may occur. By
specifying the chain of events (links in the hypotheses) it was possible to identify those
processes and pathways that are poorly understood and need to be studied.
2.1 Issues
A list of issues related to possible ecological effects of zebra mussels was
compiled, and hypotheses of effect were built for many of them. Some of the issues
did not lend themselves to the construction of these hypotheses, either because they
were very broad, or because they were concerned with reasons for our lack of
understanding of the effects of zebra mussels. The identified issues are:
1) Basic Biological Information - Before we can expect significant insight into the
ecological effects of mussels, it will be necessary to have more complete
information on the autecology of mussels in North America. Although much is
10
-------
known on the biology of European and Soviet mussels, it is not reasonable to
assume that North American mussels "behave" or function identically.
2) Translation of European and Soviet Science - Many studies on the ecological
effects of zebra mussels have been carried out in Europe and in the Soviet
Union, where they have existed for much longer than in North America.
Relatively little of this information is available in English. Therefore, there is a
need for a concerted effort to translate existing (and future) European and
Soviet publications into English.
3) Ecosystem Database - To facilitate analyses of the effects of zebra mussels, an
ecosystem database should be developed. The database should contain
information from many different lakes and streams, on biological, physical and
chemical parameters related to ecosystem functions possibly affected by
mussels. This effort would be most effective if it were to be coordinated by a
central agency or body.
4) Separation of Mussel Effects from Other Effects - Several of the hypothesized
effects of mussels could also be caused, or contributed to, by other ecological
mechanisms. For example, increases in water clarity could result not only from
the proliferation of zebra mussels, but from decreases in nutrient concentrations
of water bodies related to controls on phosphorus and nitrogen loads from
industrial and municipal effluents. It is important that researchers and analysts
consider these potentially confounding factors so that the role of zebra mussels
can be understood.
5) Differences in Aquatic Ecosystems - It is not reasonable to expect that the
effects of zebra mussels will be the same on every lake or stream. Just as
aquatic systems are not identical in their ecological, physical, and chemical
properties, so the effects of mussels will not be the same. This does not mean
that research need be carried out on every system that mussels colonize in
order to understand their effects, but rather that care be taken in extrapolating
between systems in terms of anticipating effects and responses to any control
measures.
6) Destabilization of Ecosystems - Disturbance to ecosystems through the influx
of exotics and the loss of native species renders them prone to further native
extirpations and exotic introductions. The Great Lakes of today bear little
resemblance to their pristine state. Changes induced by the introduction of
zebra mussels will likely facilitate the proliferation of further exotic species. For
example, non-native predators of mussels as well as mussel-borne diseases and
parasites may become established in the Great Lakes.
2.2 Hypotheses of Effect
Issues for which hypotheses of effect were constructed were grouped into three
broad categories: 1) food related effects; 2) habitat related effects, and 3) effects
caused by pathogens, parasites and toxics. There are many overlappings between the
effects discussed below, and some do not fit neatly into any category. They are
presented according to this scheme for convenience.
11
-------
The hypotheses are presented in the following pages as diagrams. The text
describes the key steps in the pathways or "links" between the cause and effect and
summarizes the key unknowns.
Food Related Effects
There are, in general, three types of food related effects: 1) those caused by
predation by zebra mussels; 2) those caused by the use of zebra mussels as food by
other organisms; and 3) those caused by competition for food between mussels and
other organisms. Hypotheses one to four illustrate mechanisms whereby one or more
of these types of effects may cause ecological changes.
Hypothesis 1: Zebra mussel predation on phytoplankton and detritus may lead to
changes in water clarity.
Link 1. Zebra mussels prey on a variety of phytoplankton species.
Link 2. Predation by zebra mussels will cause a decline in phytoplankton
populations.
Link 3. Decreased phytoplankton concentrations will lead to increases in water
clarity.
Link 4. Zebra mussel "predation" on detritus will cause a decrease in detritus
concentration.
12
-------
Link 5. Decreased detritus concentration will lead to increases in water clarity.
Link 6. Decreases in phytoplankton populations will cause a decline in zooplankton
populations that prey on the same species of phytoplankton as the mussels
do.
Link 7. Decreases in zooplankton populations will cause an increase in
phytoplankton that the zooplankton prey upon.
Link 8. Increases in populations of some species of phytoplankton will cause a
decline in water clarity.
Although there is evidence linking zebra mussel colonization to changes in water
clarity in Lake Erie (Mackie, presentation at workshop), many uncertainties remain
regarding the extent and mechanisms by which this effect may occur. There are
important uncertainties associated with several of the links in this hypothesis. We
know that zebra mussels prey on a variety of phytoplankton species and detritus, but
we donft know the species and size spectrum of the items consumed, or feeding rates
of the mussel. The species of phytoplankton that will be affected, and the functional
response of phytoplankton to zebra mussel predation is also unknown. Similarly
neither the species nor the functional response of zooplankton to declines in
phytoplankton densities is known, and the feedback of changed zooplankton
populations on the phytoplankton community is uncertain.
Answers to these unknowns will contribute to a general understanding of the
relationship between zebra mussels and water clarity.
Hypothesis 2: Zebra mussel predation on phytoplankton may lead to changes in the
size and species composition of zooplankton.
13
-------
Link 1. Zebra mussels prey on a variety of phytpplankton species and predation
rates may be related to phytoplankton size.
Link 2. Changes in the size distribution of phytoplankton will lead to changes in the
size distribution of zooplankton.
Link 3. Zooplankton species composition will change as size distribution changes.
Although this hypothesis is similar to part of Hypothesis 1, it is included
separately here to emphasize the species distribution of zooplankton as a valued
ecosystem component in its own right (in addition to its influence on water clarity).
Similarly, several of the uncertainties related to this hypothesis are comparable to those
of Hypothesis 1.
As noted above, mussel behavior may be different in different ecological
settings. Hence it would be useful to know whether the susceptible species and sizes
of phytoplankton in North America differ from those in Eurasia. This would help in our
efforts to understand the ecology of mussels and to predict the effects of mussel
colonization.
Hypothesis 3: Predation on zebra mussel larvae and adults may lead to changes in
fish and waterfowl populations.
Link 1. Zooplankton feeds on zebra mussel veligers.
Link 2. Some fish species feed on zebra mussel veligers.
Link 3. Some fish species feed on zebra mussel adults.
Link 4. Some waterfowl species feed on zebra mussel adults.
14
-------
Link 5. Zooplankton populations will increase in response to additional food.
Link 6. Populations of some fish species will increase in response to increased
zooplankton densities.
Link 7. Populations of some fish species will increase in response to increased use
of veligers as food.
Link 8. Population of some fish species will increase in response to increased use of
mussels as food.
Link 9. Populations of some waterfowl species will increase in response to increased
use of mussels as food, and population distributions may also change.
This hypothesis portrays the idea that predators of mussel larvae and adults may
respond to increased food availability. Many of the uncertainties related to this
hypothesis can be summarized in the following questions: What species of predators
prey on mussel veiigers and adults and to what extent are they used as food? What is
the functional response of the predators to the increased food supply?
Several different responses to increased mussel availability are possible. Some
prey species may experience a "release" from predation as predators shift their diets to
take advantage of the abundant prey available. Others may experience greater
predation pressure should the predator continue to use them in addition to mussels.
Veligers are available as food for a relatively short time. The effect of this "pulse"
of food on predators may also be important. If an over-abundance of food for a short
period of time causes predators to become "out of sync" with their environment, the
effect could be significant, not only for the predator species, but also for their prey and
any other predators that prey on them.
The web of possible ecological effects outlined above illustrates that many
uncertainties exist concerning the potential effects that zebra mussels may have on
ecosystems by serving as a new source of food for predatory species.
Hypothesis 4:
Populations of aquatic species which feed on the same phyto/
zooplankton species as zebra mussel veligers may decrease as a
result of competition.
15
-------
Link 1. Zebra mussel veligers prey on some species of zooplankton.
Link 2. Zooplankton populations which are preyed on will decline.
Link 3. Zebra mussel veligers prey on some species of phytoplankton.
Link 4. Populations of zooplankton species that prey on the same species of
phytoplankton as veligers will decline.
Link 5. Fish and other organisms that feed on zooplankton affected by veligers will
decline.
Link 6. Fish and other organisms that feed on the same species of phytoplankton as
veligers will decline.
This hypothesis illustrates possible mechanisms by which exploitation competition
may affect species which use the same prey species as zebra mussel larvae. To
understand the effect on species higher up in the food chain, we need to gain an
understanding of what species and sizes of phytoplankton and zooplankton are the
preferred prey of veligers.
For the same reasons that veligers are available as food for a relatively short amount
of time (in Hypothesis 3], they are present as predators for only a short time. The effect
of this "pulse" of predators may be as important as the effect of the "pulse" of food that
veligers supply for some species.
Habitat Effects
Zebra mussels influence the habitat of other organisms both directly and indirectly.
They compete with other bivalves for substrate, and their presence can affect nesting and
spawning habitat of fish. Their presence can also influence benthic flow regimes, water
clarity, and macrophyte populations, all of which can impact other species.
16
-------
Hypothesis 5:
Mussel colonization of hard substrates may reduce the availability of
fish nesting and spawning habitat.
Link 1. Hard Substrates are colonized by zebra mussels.
Link 2. Zebra mussel colonization will reduce the area of free hard substrate.
Link 3. Reduced area of free substrate will reduce the area of nesting habitat
available for some fish species.
Link 4. Interstitial spaces will be created by mussel colonies.
Link 5. Interstitial spaces will be used as spawning habitat by some fish species.
Link 6. Interstitial spaces will become filled with mussel feces and pseudofeces.
Link 7. Mussel feces and pseudofeces in interstitial spaces will affect their use as
spawning habitat
This hypothesis expresses the notion that the establishment of zebra mussel
colonies on hard substrates may change the availability of nesting and spawning
habitats for some fish species. Some species which use hard lake bottoms for nesting
may suffer deleterious effects as they loose suitable spawning habitat due to mussels.
Other species may be able to use the interstitial spaces created by mussel colonies as
spawning habitat.
The main uncertainties associated with this hypothesis lie in the identification of
what species are affected by each pathway and the extent to which they are affected.
17
-------
Hypothesis 6:
Zebra mussels may reduce populations of native bivalves through
competition for food and space, and by using bivalves for
substrate.
Link 1. Zebra mussels prey on a variety of phytoplankton species.
Link 2. As a result of zebra mussel use, the availability of phytoplankton for native
bivalves will be reduced.
Link 3. Native bivalve populations will decline as a result of decreased
phytoplankton availability.
Link 4. Zebra mussels will compete with native bivalves for living space (i.e. hard
substrates)
Link 5. Native bivalve populations will decline as a result of competition for space
with zebra mussels.
Link 6. Zebra mussels will use native bivalves themselves as substrate.
Link 7. Native bivalves populations will decline as a result of their use as substrate
by zebra mussels.
This hypothesis contains three pathways by which zebra mussels may reduce
populations of native bivalves. Links 1 - 3 represent exploitation competition and links
4 and 5 represent interference competition. Links 6 and 7 represent the notion that
zebra mussels, in their use of native bivalves as substrate, may impair the normal
functioning of the bivalves to such a degree that their populations decline.
Key uncertainties of this hypothesis concern the identification of bivalve species
affected by each pathway, and quantification of the degree of effect. Since there are
18
-------
several species of endangered clams in the Mississippi River and the Great Lakes,
special consideration should be given to resolving these uncertainties.
Hypothesis 7:
Changes in macrophyte distribution and abundance caused by
zebra mussels may affect fish and waterfowl populations.
Detritus
\
3
Macropnyw
Populations
1 Distribution
9
\
Sediment
Link 1. Zebra mussel colonization will lead to increases in water clarity
(Hypothesis 1).
Link 2. Increased water clarity will lead to increases in the abundance and
distribution of macrophytes.
Link 3. The amount of detritus in the water column and settling on the bottom will
increase as a result of increased abundance of macrophytes.
Link 4. Detritus will be used as food by mussels and increase or sustain their
populations.
Link 5. Macrophytes themselves will be used as substrate and will increase
mussel populations.
Link 6. Increased macrophyte populations will increase bottom sediment.
Link 7. Increased bottom sediment will decrease substrate suitability for zebra
mussels.
Link 8. Macrophytes will be used as food by fish and waterfowl species.
Link 9. Macrophytes will be used as cover by fish and waterfowl species.
19
-------
Link 10. Populations of some fish species will increase as a result of increased
macrophyte food.
Link 11. Populations of some waterfowl species will increase as a result of
increased macrophyte food.
Link 12. Populations of some fish species will increase as a result of increased
macrophyte cover.
Link 13. Populations of some waterfowl species will increase as a result of
increased macrophyte cover.
This complex hypothesis portrays the means by which fish and waterfowl
populations may be affected by changes in macrophyte abundance caused by zebra
mussels. Fish and waterfowl populations will likely benefit from the additional food and
cover provided by the increase in macrophytes caused by zebra mussel colonization.
Link 1 is a summary of Hypothesis 1. Links 4 and 5 represent positive feedbacks
between macrophyte establishment and mussel populations; links 6 and 7 represent
negative feedback. Links 8-13 represent the response of fish and waterfowl
populations to macrophytes.
Many significant questions arise from this hypothesis. Since Hypothesis 1 is
represented in Link 1, all the uncertainties relevant to that hypothesis are also relevant
here. All of the feedback mechanisms are hypothetical at present; quantification of
each of them would be useful in understanding the relationship between zebra mussels
and macrophytes. Similarly, observation of the quantitative response of fish and
waterfowl species to increases in macrophytes caused by zebra mussels could add
significantly to understanding the ecological effects of mussels.
A key issue related to this hypothesis is the distinction of zebra mussel-related effects
from other effects. Many ecological processes affect fish and waterfowl populations;
how can the effects represented in this hypothesis be distinguished from those caused
by other mechanisms?
Hypothesis 8:
Zebra mussel colonies may affect benthic flow regimes which in
turn may affect aquatic habitats.
\ 7
20
-------
Link 1. Zebra mussel colonization of bottom substrate will cause changes in
benthic flow regimes.
Link 2. Particulate re-suspension will be increased due to changes in benthic flow.
Link 3. Water clarity will decrease in response to increased particulate re-
suspension.
Link 4. Toxics concentrations in the water column will increase with particulate re-
suspension.
Link 5. Changes in benthic flow will cause changes in suitability of micro-habitat
for macrophytes.
Link 6. Macrophyte colonization will be affected by changes in micro-habitat
suitability.
This hypothesis portrays some of the impacts that could result from changes in
bottom flow caused by mussel colonization. The effects of changes in benthic flow
could be far more extensive than those represented in this hypothesis (e.g., change in
water clarity could cause changes in macrophyte distribution and vertebrate
populations similar to those in Hypothesis 6, increased toxic concentrations in the
water column could have deleterious effects on biota, etc.).
Before addressing the magnitude of effects on the endpoints in the hypothesis"
(water clarity, toxics in water column, and macrophyte colonization), some effort should
be devoted to understanding and quantifying the first link, namely, determining how
much mussel colonies alter benthic flows. Similarly, the impacts of a changed flow
regime on particulates and microhabitat need to be understood, and possibly
quantified, in order to understand the final links in the hypothesis.
Hypothesis 9:
Increases in water clarity caused by zebra mussels may lead to
changes in the heat distribution of the aquatic environment and
therefore changes in physical and biological processes.
21
-------
Link 1. Zebra mussel colonization will lead to increases in water clarity
(Hypothesis 1).
Link 2. Heat distribution of the aquatic environments will be affected by changes
in water clarity.
Link 3. Aquatic physical processes will be affected by changes in heat distribution.
Link 4. Biological and metabolic processes will be affected by changes in heat
distribution.
This hypothesis represents a substantial series of ecological and physical effects.
As in other hypotheses presented here, the endpoints of this hypothesis are also the
initial steps in far-reaching ecological chains of events. Since Link 1 in this hypothesis
represents all of Hypothesis 1, all the uncertainties and questions related to Hypothesis
1 are applicable. A key in this hypothesis is the quantification of the relationship
between water clarity and heat distribution. This is an enormous issue with many
permutations and side-tracks (e.g., considerations such as ambient temperature and
light regimes must be considered). Answering this question alone would be a
significant research effort.
Pathogens. Parasites and Toxins
The last group of hypotheses are concerned with the introduction or
redistribution of new parasites, pathogens and toxins, along with or through the impact
of zebra mussels.
Hypothesis 10:
Zebra mussel colonization may lead to a re-distribution of toxins in
the aquatic community.
22
-------
Link 1. Zebra mussel colonization will cause a shift to a benthically-oriented
community.
Link 2. The total amount of toxins in the benthos will increase as a result of
increases in benthic biomass.
Link 3. Zebra mussel toxin loads will increase as a result of increased toxins in
the benthos.
Link 4. The total amount of toxins in the water column will decrease as a result of
increases in benthic biomass.
Link 5. Zebra mussel shells will act as sinks for toxins.
Link 6. Toxin concentrations in benthic fish will increase as a result of predation
on zebra mussels and other benthos.
Link 7. Toxin concentrations in waterfowl will increase as a result of predation on
zebra mussels.
This hypothesis illustrates mechanisms by which toxins in the aquatic ecosystem
may be redistributed as a result of zebra mussel colonization. Link 1 represents the
series of ecological events that could lead to a re-distribution of energy and biomass in
aquatic communities. This link in itself could be the subject of an intensive research
effort. Each subsequent link in this hypothesis has uncertainties and questions
associated with it. Basically these questions relate to determining whether the
hypothesized link actually exists, and if so, quantifying the magnitude of the effect. For
example, for Link 7 the two questions would be: 1) do waterfowl accumulate toxins as
a result of eating mussels and other benthic organisms?, and 2) what is the effect on
waterfowl of ingesting toxins from mussels and other benthic organisms?
23
-------
Hypothesis 11:
Zebra mussels may pass exotic and native parasites on to native
clams, fish, and birds.
Link 1. Zebra mussels may act as intermediate hosts for exotic parasites (most
likely trematodes).
Link 2. Zebra mussels may act as intermediate hosts for native parasites (most
likely trematodes).
Link 3. Trematode parasites have a free-swimming larval stage.
Link 4. Zebra mussels will be used as food by some fish and bird species.
Link 5. Trematode larvae will infest native bivalves.
Link 6. Trematode larvae will infest local fish populations.
Link 7. Trematode larvae will infest local waterfowl populations.
Link 8. Fish which feed on infested mussels will become infested.
Link 9. Waterfowl which feed on infested mussels will become infested.
This hypothesis illustrates mechanisms by which some fish and waterfowl
species may become infested by native and exotic parasites which use zebra mussels
as an intermediate host. There are two significant issues related to this hypothesis.
First, we must identify zebra mussel parasites. At present there is no complete listing
of organisms which parasitize zebra mussels in North America, and little work on this is
being done. Second, we need to quantify what effect, if any, parasites which use zebra
mussels as an intermediate host have on fish and waterfowl species.
24
-------
3. Rate and Extent of Spread of the Zebra Mussel
There is no question that zebra mussels are spreading in North America. The
question is, can we predict how quickly they will spread, and to which area. The rate
and extent of spread is generally influenced by the suitability of the habitat and by the
means or vectors available to enable the organisms to move from one location to
another. Habitat suitability constraints are important at the scale of a water body,
whereas dispersal vectors are important both at this scale and on a larger scale. Four
distinct scales with distinct questions were identified related to both rate and extent of
spread:
1) Water-body
How do zebra mussels spread within a lake and how may they be
transported from a lake to an adjacent water body?
2) Catchment
How do zebra mussels spread through a catchment and what are
the limiting factors?
3) North America
How are zebra mussels capable of spreading throughout North
American waterways and what are the limiting factors to continental
spread?
4) Global
How are zebra mussels capable of spreading across ocean bodies
and what are the limiting factors to global spread?
Discussion was likened to a model-building exercise. A list of factors was
developed that constrain the suitability of zebra mussel habitat. The number and
strength of influence of these limiting variables defines the ability of zebra mussels to
succeed in a particular area. Where a habitat has many limiting components (e.g.,
temperature, calcium, etc.) we can predict a low probability of colonization and minimal
threat of spread. Conversely, where few limiting constraints exist we can predict a high
probability of colonization and a maximum threat of spread.
Movement from lake to lake is largely a function of vectors, but these are difficult
to model. Instead, a geographic information system was proposed that would assist in
keeping track of current mussel distribution and areas to which they may spread
based on both habitat constraints and dispersal vectors.
3.1 Habitat Constraints
The following section presents our understanding of the habitat constraints that
affect the spread of zebra mussels. For each constraining factor it was determined
whether or not the limits are known for Europe or North America or both. Where
possible, interacting and confounding factors that limit the rate of zebra mussel spread
25
-------
were identified. A more thorough review would require an explicit definition of the
relationships between factors that constrain zebra mussel spread and the factors that
determine zebra mussel abundance.
Where insufficient knowledge existed to adequately define key habitat
constraints, an information gap was identified, and a research question was posed.
The constraints are divided into chemical, physical and biological categories, and are
summarized in the following tables.
Table 3.1 Chemical constraints on zebra mussel growth
Parameter
Ca>
M|2*
dissolved
O2
temperature
pH
NV
toxins
Threshold Value j Origin
1 of Data
12 mg/L
13 mg/L
2 8mg/L
limiting < 36% sat.
opamum: 80-85% sat
unfavourable 5 6 mg/L
filtration stops at <3°C
and>30°C
a significant decrease in
growth occurs at 10-15°C
a 12°C needed for occyte
release
upper limit of successful
veliger development is 26-
27°C
optimal growth at 17-
<6.5
50% mortality within 6-9
hours at pH 5.0
need > 1.5-2mg/L
upper limit 16-17 mg/L
salinity NaCl
a stable reproducing
population will establish at
600-800 mg/L chloride
U.S.S.R
U.S.S.R
L. Sup.
U.S.S.R
Jonassen
1972
Dugga
1966
U.S.S.R
U.S.S.R
U.S.S.R
U.S.S.R
North
America
Research
Questions
1 What are the other limiting
canons?
2 What are the upper ionic
calcium concentration limits
in North American waters?
3 How do the calcium
thresholds change in
response to chanzes in uH?
4 What are the differences in
dissolved oxygen needs
between adult and veliger?
5 What are the winter
temperature thresholds of
zebra mussels in North
Amenta?
6 How do zebra mussels
respond to temperature
fluctuations?
7 What are the effects of
organic acids on zebra
mussels? W"hy are zebra
mussels not found in North
American bogs streams.
which have an increased
concentration of organic
xids?
8 What are the effects of
sodium in North American
lakes?
9 What toxic elements do
zebra mussels
bioaccumulate and in what
concentrations?
Notes
at increased temperatures,
zebra mussels need more
dissolved oxygen
at pH 5 0, toxicity effects
expressed through sodium
and water increase
in the absence of sodium,
zebra mussels live
approximately 12 hr with
"normal" pH
zebra mussels can
accumulate toxins and not
pensh
26
-------
Table 3.2 Physical constraints on zebra mussel growth
movement
subttrat*
depth
length of
growing
seuon
water level
fluctuation
Llaltlni
Constraint
need hard, soud surface
cui spend 6-7 days out of
water before desiccation
Origin
of Ditt
U.S.S.R.
U S.S.R.
N'onh
America
USSR.
Resttrcb
Question*
1 If food uid oxygen ir«
sufficient, a depth limiting?
If so. what does this imply
for munieiotl witer intake?
1 Does the length of the freeze
effect ubri mussel
reproductive cycles tnd
soouii'jon trowth1
Notii
w«ttr movement through
flow ind waves coniidered the
moil important fictor
water movement allows for
constant import of food
source* (phytoplankton) «nd
shallow water bodiei with i
lot of sill »U1 linut tebra
Table 3.3 Biological constraints on zebra mussel growth
Organism
fish:
sheephead
bream
rotch
eeU
diving ducts
phyto-
plankton
diseases
paruttci:
AspifOt&ntr
bacteria
Limiticj
Constraint
< possible prey species
prey species
up to 90-99% cumulation
of zebra mussels in small.
shallow lake*
the veliger is dependent on
ample small plankton
population!
sufficient chlorophyll
neceuary for normal (hell
growth
need 20-50 mg/L in
flowing waur (eutrophie
streams)
potential for retraction of
zebra muuel growth rate and
elimination of the population
bacteria known to have
little effect on zebn mussel
oooulitions
Origin
or Data
N'onh
Amenc*
Nether-
lands
Sprung
1988
U.S S.R.
U.S.S.R.
Research
Questions
I What native North A. sncan
organisms prey on ze:ra
mussels?
2 \V"hat roie may leeches play
as predators?
3 What is the effect of lirrjted
phytopluikton in
oligouophic systems?
4 What diseases rr.iy limit the
rate of rebra mussel rrowih1
S Does this parasite exist in
North America and can it be
effectively used as a conuol
mechanism?
Notes
fish as prey ue likely to
have uttia effect in
dampening the rate of rebra
mussel spread
zeora mussel diet is 10"«
phytoplankton. 90% deuims
at 1mm in length feed on
dead organic matter
at 1cm, stan feeding on
looplankton
Aspijogasitr appears to be
iebra mussel-specific; causes
stinlity through action in the
jut; this effects reproductive
success and population
viability.
27
-------
A significant amount of the information regarding the chemical thresholds to
zebra mussel survival and the limiting biological and physical factors comes from
Soviet and European research. Although this data is important as a starting point, the
physical and chemical properties of North American lakes are not all similar to these
European lakes in which zebra mussels were studied. Because the North American
zebra mussel may be genetically different from the organisms studied overseas, the
limiting factors to zebra mussel spread cited in the European literature may not be
relevant to North America. Although we should utilize the valuable European
experience and information, it is necessary to continue work to identify constraints to
zebra mussel growth in North American lakes.
3.2 Population Growth and Spread within a Lake
The list of constraints to zebra mussel success indicates factors which may limit
population growth and slow the rate of spread. The rate of increase will be rapid or
slow, depending on the constraints (such as water temperature, calcium and
magnesium availability, pH, chlorophyll availability, water flow, dissolved oxygen levels
and the length of the growing season) present in the lake. Some of the constraints
operate through density dependent mechanisms, so that their influence becomes more
significant at high population levels. This means that the rate of increase declines over
time and the total number of zebra mussels in the lake reaches a maximum level. The
number of mussels is a function of mortality rates, recruitment levels and rate of
growth, which are dependent upon the influence of the habitat constraints. By
determining these rates in response to habitat constrains, we can predict how a
population of zebra mussels in a lake will increase over time.
The maximum population level achieved is very much influenced by the area of
suitable bed or habitat available to the mussel. Where the area of bed is small, the
maximum population will be small. A specified population level will be reached sooner
in a lake where bed area is not constrained than in a lake where there is only a small
area of suitable bed. Physical constraints such as unsuitable substrate will prevent
zebra mussel growth across the whole lake.
Finally, some population control mechanisms such as parasites, diseases and
predators may become effective only after an initial peak has been reached. There
may be lag times related to their appearance in the water body or in their ability to
reach high enough levels to be effective. Zebra mussels may reach a stable high level,
or they may reach a peak that declines over time to a lower stable level. The Soviet
experience of introductions to new areas has been a peak population followed by a
rapid decline to a lower more stable level.
As control measures are applied, the rate of increase of zebra mussels in the
lake should decrease. Effective controls will either slow the increase or decrease the
maximum population size.
Increased knowledge of the effectiveness of various chemical, physical and
biological constraints to zebra mussel population growth will provide useful information
to those attempting to develop effective local or lakewide control programs. Hence
research on limiting constraints is not only relevant for predicting the rate and extent of
spread, but also for the development of viable control programs.
28
-------
3.3 Extent of Spread
Due to the adaptive nature of zebra mussels and the poor knowledge of
dispersal mechanisms, it would be difficult to adequately predict the extent of spread at
any specific time. Instead the group focused on the potential range limits of the
mussel. Quite simply, the range limits are defined by habitat constraints.
The simplest way to represent the impact of all the identified constraints would
be through the use of a Geographic Information System (GIS). This will permit the
user to provide a series of overlays based on maps that represent various constraining
parameters to zebra mussel colonization. As an example, one map may show calcium
levels throughout the Great Lakes basin, another may show temperature gradients, a
third may represent pH levels, etc. On each map, areas with limiting zebra mussel
habitat are highlighted. The aggregation of these constraint maps will result in a
product that shows which geographic areas are the most likely to be invaded by zebra
mussels due to a lack of limiting conditions. As map data is digitized to be used in a
GIS, it becomes easy to edit and manipulate, so the GIS would serve as a vehicle for
maintaining a current database.
From the evidence that exists now the group estimated that in Europe the zebra
mussel range extends from the Caspian Sea in the south to the White Sea in the north.
The mussel has yet to be identified in Asia or Siberia. It's Asian absence may be a
function of the turbulent waters common to the area, while the Siberian constraint is
the cold and pristine waters where the amount of phytoplankton as a food source is
limiting.
In North America, the present information indicates that the species occurs
throughout the Great Lakes, from Thunder Bay, Ontario, south to southwestern Lake
Erie, and from Duluth, Minnesota, east to Quebec City where salt water meets fresh
water. The species is not yet close to being limited by habitat constraints and is
expected to eventually spread throughout most of North America.
3.4 Rate of Spread from Lake to Lake
Modelling the rate of spread of zebra mussels from water body to water body,
across North American and from continent to continent would be very difficult and full
of uncertainties. The difficulty stems from the fact that rates of spread from one water
body to another are completely dependent on the dynamics (type, frequency, distance,
substrate) of the dispersal vector. If there is frequent opportunity for the organism to
interact with a vector and to be transported in favorable conditions to new habitats,
rates of spread across water bodies may be quite high. On the other hand, restricted
opportunity to contact favorable vectors will result in low rates of spread across water
bodies. The prediction of rates of spread between lakes requires knowledge of the
frequency and probability of spread by specifically identified vectors as well as
information on where the vectors are going.
Two major categories of vectors were identified: natural, and those based on
human activities. The human influenced methods of zebra mussel dispersal include:
1) recreational boating and angling;
2) commercial vessels;
3) man-made canals/ irrigation ditches;
4) aircraft pontoons;
29
-------
5) intentional release of zebra mussels;
6) research equipment;
7) litter (garbage).
The natural dispersal mechanisms include:
1) currents;
2) waterfowl (i.e., on feet);
3) insects.
A veliger requires a moist medium to successfully disperse (e.g., ballast tanks,
canals, bait buckets, currents), whereas an adult requires a solid substrate onto which
it may attach (e.g., boat hulls).
An estimate of the rate of spread across North America may most effectively be
accomplished through mapping exercises. The maps would show known areas of
zebra mussel colonization and display canal routes and shipping lanes, since these are
the most common and most efficient vectors. By knowing the routes of the major
vectors we can estimate the route of dispersal of the mussels.
A Geographic Information System (GIS) would be an ideal way to display the
maps and vectors. A GIS would give the user the ability to visually observe where
mussels are now and where they will probably end up given the nature of the
constraints and dispersal vectors in the surrounding water bodies. For example, if an
area of high concentration of mussels rests adjacent to an area that the map displays
as having few limiting constraints and the lakes are connected by canals, the
probability of mussel infiltration into the new lake is high. The GIS system would have
the ability to represent:
1) prime zebra mussel habitat (constraints map);
2) where the mussels are found now;
3) major movement corridors;
4) an indication of potential range limits.
By knowing where zebra mussels are, what habitat they like, and what vectors
are available for movement, it should be possible to estimate not only where they will
go, but also to predict the routes of spread and the order of arrival in various water
bodies. A simulation model could be used in conjunction with the GIS model to predict
colonization probabilities and rates of spread. The combined system would perform a
series of analyses to determine successive infestations given the routes and
probabilities for dispersal as well as the habitat constraints. Predictions of the pattern,
extent and relative timing of spread could then be made.
4. Control of Established Species
The control of established introduced species, or even of zebra mussels
specifically, could be the subject of extensive scientific and practical management
literature. Discussion was limited to 1) general issues related to population-wide
control of established aquatic species, with some specific consideration of the zebra
mussel, and 2) local control of the zebra mussel in response to specific problems
caused by this organism. A framework was developed to evaluate local control
measures.
30
-------
4.1 Population Control of Established Species
Once an organism has been introduced and is successfully exploiting its new
habitat, it will be difficult or impossible to totally eradicate it. There are no poisons that
are entirely specific to any organism; even those that are designed to target a certain
taxonomic group are only relatively more poisonous to that group than to other
groups. Thus it is not possible to get rid of one species without at the same time
affecting others, often including humans. Alternatively one could try to alter the
environment in such a way that it is no longer hospitable to the new organism; but this
is likely to have ecosystem-wide ramifications. Even biological control methods, such
as predators, parasites and diseases that affect the introduced species are rarely so
narrow in their impact that other parts of the ecosystem are unaffected. Any attempt
to control a natural system requires us to address the complexity of the whole system.
In order to control a whole population one must target a significant proportion of
either the individuals or the habitat. Control on a continent wide level is unlikely; the
natural system generally overwhelms any human actions. To control any organism
that has the ability to disperse (such as the zebra mussel in its larval stage), action
would have to be taken at least on the scale of a continuous body of water, such as a
lake. Since this is a daunting task for anything as large as the Great Lakes, one would
only consider population scale control if the ecosystem effects of the invading
organism were unacceptable or had serious socio-economic consequences, such as
an adverse impact on fisheries.
Even though population level control in the Great Lakes is not a feasible
alternative, methods were discussed which one might consider if drastic measures
were to be required. Furthermore, populations in small, isolated bodies of water could
be managed, and hence the potential methods may interest some people.
Changes to Habitat
Lake chemistry could be changed to make it unattractive to the zebra mussel
through judicious additions of chemicals which would change the level of Ca, K, Mg,
oxygen or pH to an unacceptable range for the mussel. Other organisms would of
course also be affected. Such changes may already be happening either naturally or
unintentionally in some lakes; for example, changes in lake pH as a result of acid rain.
Similarly in small bodies of water we could influence physical factors which limit zebra
mussel distribution, such as the nature of the substrate, temperature, current, depth,
and turbidity. It is possible to deposit sand on the bottom of a lake in order to
discourage settling of the mussel larvae.
Biological Control
Since biological control is the only population control measure which has the
potential to both persist and amplify over time, it is the only method we could use over
extensive areas or a long time period. The use of imported predators, parasites and
diseases is very risky, but some effort should go into investigating the options now, as
responsible research of biological control methods requires a long time.
Several of the natural enemies of the zebra mussel, (e.g., European carp,
Caspian goby, and a bacterial disease) may already have been inadvertently imported.
In a few more years these biological control agents may become well established and
cause a crash in the mussel population. The European experience with introductions
31
-------
of the zebra mussel to new areas suggests a general pattern starting with a high build-
up followed by a crash and then a lower stable level.
Finally, native species may over time learn to exploit the zebra mussel and play a
part in controlling their population levels. Diving ducks, such as scaup, are already
becoming more abundant in zebra mussel areas, and it is known that in shallow
European lakes ducks are a significant mussel predator. Similarly, native fish such as
the drum, sheepshead, and buffalo may become important predators. Investigations
concerning potential control (and other impacts) by existing native and non-native
species are in progress.
4.2 Control of Problems Caused by Zebra Mussel
The difficulty in controlling whole populations does not imply helplessness in
dealing with local abundances which cause problems. In the few years that the zebra
mussel has made its presence known, many potential control methods have been
identified, some of which are currently in use and are effective, and others are being
developed. The chief concern is to identify and develop methods which have no
adverse effects.
It was not possible to evaluate or prioritize all the potential control actions at this
workshop. To do so would take much longer and will require expertise in a wide
range of specialties ranging from ecology to engineering to chemistry, hydrology,
invertebrate physiology, sociology, etc. Because the problems caused by the zebra
mussel are tangible and the impacts are felt by many people, the funding available for
the research of control methods is larger than that usually available to combat
introduced species. Our knowledge is growing quickly. However, not all of the current
research information is available, as some of it is proprietary with the intention of
commercializing solutions to problems caused by the zebra mussel.
Problems caused bv the zebra mussel
Many of the problems caused by the zebra mussel are well-known, but most
discussions focus on one problem or one perceived issue. The following table
provides examples of the types of problems encountered:
Table 4.1 Typical problems caused by the zebra mussel
Shipping
Boating
Navigation Structures
Domestic Water Supply
Industrial and Power (once-
through cooling systems)
Recreational
all shipboard systems using cooling water,
including ship power, fire control, etc.
cooling water for engines, hulls
bridges, docks, buoys, etc
intake clogging
water quality
intake clogging
fouling of internal machinery/pipes
cottage water supplies
fouling of beaches with shells etc
32
-------
Actions available to control the zebra mussel
Many lists of actions have already been developed. The following table, which is
not exhaustive, presents the major types of actions suitable for controlling the zebra
mussel. Since any action detrimental to life can potentially be used to control the
zebra mussel if it can be applied in a suitably contained fashion, the list of actions is
long. Some of them have been used for other problems, some of them are currently
being developed, and some are only ideas.
Table 4.2 Actions for controlling the zebra mussel
Shipping
BoillDf
Navigation.
Structure!
Dom«itlc
watir lupply
Industrial
Cooling
Rtcrtatlon
Chtmlcil
abiauve coatings
tbluisf coaunp
immersion btihj
abiauve coatings
oxidizing chem.
oxidizing cnem.
other chemic.
Mechanical
scrtpuii
hydroiaacmg
scraping
hvdjoiincing
scraping
ill
ill
scrip in(
CbuUdonn*)
_ Biological
local predator
Dooulauonj
local predator
copulations
Physical
h«»t
coatin|i
electromagnetic
comae
flushing
coatings
flushing
acoufDc
heal
elecmcirv
rdteil
ultraviolet
acouiac
electromagnetic
filteri
ultraviolet
acousac
electromagnetic
Suitability of actions to problem types
Although it was not feasible to evaluate control actions in detail, we did attempt
to identify which of the above actions were most suitable or promising for each
problem area.
Table 4.3 Control actions suitable for major zebra mussel problem areas
Chemical
oildlilng chemicals
chlorine. various forms
ozone
permangansie
hydrogen peroxide
Don-oxidizing
chemicals
moliu3cicid£3
fury acids (e.g. soaps)
dispenanu
C2TOOO (feoTn^jf
bisulfite
scaling agents
ablacve coa&ngs
Mechanical
removal
flow brushes
Pigging
scraping
hydrolancing
roboDc scrapers
Engineering/ Design
closed loop cooling
deep water intakes
double or large pipes
Physical
screens and filters
strainers
backwash strainers
vortex strainers
infiltration beds
sand filters
biofilters
other
bamercoaongs
heal
ultraviolet
pressunzaooa
acoustics (ultra + mfrasound)
Hushing
magnetic fields
electro- shocking
irradiation
cathodic protection
Biological
parasucs
diseases, natural and
bioengineered
geneoc sterilization
pheromones, anractants
predaicn
human predan on
(e.g. clam-meal industry)
33
-------
4.3 Framework for Evaluating Local Control Actions
In order to evaluate the suitability of any action for controlling various problems
induced by zebra mussels, a number of questions must be asked. The discussion
group identified a list of questions which should be incorporated in an evaluation
framework:
1. Is this a crisis, short-term, or long-term control effort?
An unanticipated and relatively sudden realization of a problem generated
by the zebra mussel can easily be regarded as a crisis situation,
especially if critical water supplies are being drastically curtailed. The
control methods suitable for dealing with this situation are different than
those one would wish to use on a recurring basis, or for a long-term
problem management or prevention procedure. Furthermore, different
levels of impact may be deemed acceptable for dealing with a crisis than
for on-going control.
2. What is the control strategy?
Control may be designed to prevent settling or to kill and/or remove the
mussels from the site where they cause problems. Timing, intensity,
frequency and site of the action must be specific to each installation. In
order to evaluate the effects, the details of the control strategy should be
specified. In order to develop an appropriate strategy the effects of
alternate strategies must be considered. A control strategy is likely to
consist of a mixture of control actions; and both effectiveness and impact
need to be evaluated for the whole package. Unfortunately there is no
simple solution, though some generalities do hold and experience will
enable rapid designs of effective and non-impacting strategies.
Specific attributes to be specified in a control strategy include:
Under what circumstances will the control be required? What
tolerance levels of mussel infestation need to be identified.
When will the control be applied? - this should be specified in terms
of time of year, timing with respect to the life cycle of the mussel,
and timing with respect to the process being protected.
Where? - in what geographic areas, and where in the system being
protected.
How will the control be applied? - not only in terms of specific
practices, but also in terms of how often and how long.
« What intensity level of control is considered adequate? For
example how much chemical or other application (heat, UV etc.)
will be used?
34
-------
« What contraindications to the use of this control should the user
consider? Are there any potential interactions with the existing
process? (chemical interactions, corrosion, etc.)
How will the end products of the control be disposed of (including
the organisms removed or killed)?
3. What are the costs?
Both start-up and maintenance costs must be considered; the relative
importance of each will vary depending on anticipated future need for
control. If costs are too high, the control may be unacceptable to the
user or may invite undesirable shortcuts.
4. How effective is the control method?
The user will need to know how effective the method is, and will need to
have some measure of the probability of a desired level of effectiveness.
This may entail some form of on-going monitoring for level of control
achieved.
5. Are there any environmental effects?
One of the prime concerns associated with many control measures,
particularly the chemical ones, is what other environmental impacts they
will have. This includes not only direct effects of a control action, but also
the effects of any by-products or end products. It is also necessary to
consider effects of the disposal of mussels that are removed from problem
areas. Since there is considerable uncertainty in respect to environmental
impacts, there is a need to research and to monitor. In order to monitor,
suitable measurable indicators will have to be identified.
6. Are there any social, economic, or health effects?
This is similar to the environmental effects issue, except that the domain is
socio-economic rather than ecosystem. Some socioeconomic effects may
be mediated through the ecosystem (as in bioaccumulation of toxins).
Again, uncertainties, indicators, monitoring and research needs should be
specified.
In summary, we can characterize a desirable control action as one that is facility-
specific and consists of several actions in an integrated control strategy. The strategy
should be relatively inexpensive, and the environmental and socioeconomic impacts
must be socially acceptable. In general, a good strategy will be adaptive, both in
terms of being responsive to changes in the problem or ayailable control methods and
in terms of learning to live with the problem rather than trying to eliminate it.
Sample Applications of Framework
In the process of developing the evaluation framework, three of the control
methods were considered in some detail. These were chosen to represent a fairly well
understood measure (chlorination), a measure which has not yet been applied but
35
-------
which is likely to be non-controversial (treatment of ship water systems with heat), and
a treatment method with a large number of uncertainties related to environmental
effects (molluscicide). The following discussion is not intended to be complete, but
rather to provide a superficial view of how the evaluation framework could be applied.
A focussed effort would synthesize a more extensive set of information, and the
framework is likely to be modified as a first step in the process of a serious evaluation
effort.
Chlorination with Sodium Hypochloride
Chlorinatipn is the best understood and most commonly used control method. It
is already practiced for reasons other than zebra mussel control in most municipal
water supply systems, and in Europe it is routinely used to control zebra mussels in
industrial water systems.
1. Is this a crisis, short-term, or long-term control effort?
Chlorination is considered a short-term solution in North America, though it is
known that some level of Chlorination for zebra mussel control is routinely used
in Europe.
2. What is the control strategy?
Several strategies are possible, and the one chosen would depend on the
specific purpose, the population level of the mussels, and the installation:
a high dosage to kill the mussels could be intermittent, a pulsed high
dose, or continuous for a specific period (e.g., 3 weeks at the end of the
season)
a low dosage to prevent settling of veligers would be used continually
during the season when dispersal occurs
System characteristics which determine the control strategy include:
flow rate of system
plumbing of system
interaction with other chemicals in system
byproducts which may be generated
potential corrosion problems (oxidants promote corrosion)
3. What are the costs?
Chlorination is one of the least expensive alternatives:
$50,000 to $5 million to retrofit system
operating cost for 2x106 m3 day = $80,000
4. How effective is the control method?
Chlorine is effective; it is already used, and the effectiveness characteristics are
relatively well understood. The problem is translating the theory to practice;
36
-------
many factors influence the concentration levels in the water system. A
monitoring system, such as on-line chlorine analyzers or a bioassay at the end of
the line is needed.
Uncertainties
In spite of the well-understood nature of this chemical, there are still
unknowns with respect to minimal effective levels.
5. Are there any environmental effects?
Chlorine kills indiscriminately; it is dangerous to all life forms.
Uncertainties
Dechlorination by-products and the mitigation of these are not well
understood.
Should we use total loading standards rather than emission limits? Which
is the better indicator to monitor?
6. Are there any social, economic, or health effects?
Chlorine gas is a safety issue.
Uncertainty
Dechlorination by-products, such as THM effects in water treatment plants
are not well understood. Standards of use for chlorination and
dechlorination are needed.
Two general observations emerged from the discussion of chlorination as a
control method. First, although this is the chemical control method with which we have
the most experience there are still uncertainties associated with its effects. Second, it
became clear that the strategy for use is dependent on individual circumstances; no
single guideline or application technology will be suitable for all situations.
The possibility of biomonitoring for low levels was discussed. Although biological
detectors may be better, they may not be acceptable in regulatory and compliance
matters. It may be easier to specify and enforce regulations based on instrumentation
than on biological responses, and some people may distrust the accuracy of the latter.
Heat for Control of Ship Water Systems
Heating the water in the sea chest (the multiply screened water intake area in the
hull of a ship) promises to be a relatively simple and benign control method. This has
not yet been tried, but heat has been used in other water systems.
1. Is this a crisis, short-term, or long-term control effort?
At the moment the use of heat as a control mechanisms is considered a
temporary solution, until something better can be found.
2. What is the control strategy?
The water system would be subjected to periodic heat shock; at about 1-2 week
frequency in the sea chest, with piping treated during shut-down.
37
-------
3. What are the costs?
for a ship less than 200 feet the retrofitting will be about $15-$20,000;
price will increase nonlinearly with bigger ships.
maintenance costs will be minimal, as existing heat and staff would be
used.
4. How effective is the control method?
The effectiveness of temperature for killing mussels is fairly well understood and
the relationship between temperature and duration of exposure is documented.
Uncertainty
There may be temperature effects on the plumbing system. Heat causes
expansion, and the rate of heat conduction to adjacent areas may cause
some minimal mechanical problems.
5. Are there any environmental effects?
The total amount of heat to be diffused is minimal in respect to the volume of
water involved.
Uncertainty
As the mussels are removed in port there may be an accumulation of
dead mussels on the lake bed which may have further impacts either
through decay processes or changes in the substrate.
6. Are there any social, economic, or health effects?
None are anticipated.
Molluscicide in Industrial/Power Plant Cooling System
Any biocide is potentially harmful, even if not lethal, to organisms other than the
target organism, and hence should be used with great caution. As many users believe
that molluscicides are totally harmless to other species, the required caution is not
always observed. These products are in use, but there are still many uncertainties in
respect to their effects.
1. Is this a crisis, short-term, or long-term control effort?
The use of a molluscicide is a crisis solution, one that is generally far more
powerful than required. Molluscicides may possibly be appropriate when
there is an immediate and unexpected threat to critical services. However,
as the zebra mussel becomes established, an unexpected crisis should
not emerge as there should already be a control strategy in place.
2. What is the control strategy?
Molluscicides are generally applied for a period of 6-7 hours, and where
they are used as a general control, this would be repeated 3-4 times a
year.
3. What are the costs?
The use of molluscicides is particularly attractive from an operational point
of view. No retrofitting is required, there are no worker safety concerns,
38
-------
and currently there is no time consuming regulatory procedure.
Furthermore, molluscicides are relatively inexpensive.
4. How effective is the control method?
Molluscicides are known to kill zebra mussels at high doses.
Uncertainties
Dosage requirements are not understood. Dosage is expected to
vary depending on whether the intention is to kill or to detach, and
whether adults or veligers are targeted.
The effect of the molluscicide is temperature dependent (related to
metabolic rate), but the exact nature of this is not known.
It is not clear how dead organisms are to be removed from the
system being treated.
5. Are there any environmental effects?
The normal procedure for "detoxification" is to use bentonite clay to bind
the molluscicide after it has had a chance to affect the zebra mussels. The
poison binds to the clay in the form of a cation.
Uncertainties
The molluscicide may be easily displaced from the clay by a
stronger cation and thus released to environment.
The persistence of the molluscicide in the ecosystem is not known;
there may even be bioaccumulation.
Molluscicides are not specific to the zebra mussel, so all mollusks
in a system are at risk. Furthermore molluscicides may have
impacts on other aquatic organisms over time.
6. Are there any social, economic, or health effects?
None are known.
5. Prevention of New Introductions
There are two aspects to the prevention of new introductions; namely methods
for preventing future introductions of new exotic aquatic species into the Great Lakes,
and methods for preventing established exotics in the Great Lakes basin from
spreading to other regions. The group discussed unintentional introductions as well as
intentional "non-legally sanctioned" introductions such as smuggling exotic flora/fauna
and introduction by amateurs, but did not consider "legally sanctioned" introductions
such as exotic species brought in for aquaculture or for biological control programs
(although it was recognized that not all legally sanctioned introductions were
beneficial). Rather than focusing on the zebra mussel, the group decided to consider
the general problem of introductions.
Potential vectors through which exotic species may be introduced were identified,
then ranked according to their relative importance and manageability. Possible
39
-------
management actions were identified to target each of these vectors. Finally, some of
the more promising management actions were considered in greater detail, then
evaluated according to specific criteria. During this discussion, a number of research
needs and recommendations were identified.
5.1 Vectors
Species enter a new system in a variety of ways or vectors. Each of these
vectors has different characteristics, and is amenable to different levels of control and
different control methods. The following possible vectors for the introduction of new
species in aquatic systems were identified:
natural
abiotic dispersal mechanisms such as wind or currents
dispersal on or in other mobile organisms (waterfowl)
ships
ballast water
solid ballast
biofouling
cargo
canals
and other water diversions or water transport
accidental
bait, and the water in which bait is contained
aquaculture escape
escape from aquaria/ponds
importation with aquaria/aquaculture species
recreation
pleasure craft
aquatic equipment (e.g., windsurfers, scuba gear)
deliberate
releasing exotics for aesthetic reasons or profit
aircraft transport
ground transport
trucking
rail
nursery material
scientific collection
collected material
collection equipment/vessels
40
-------
tourists
construction and building materials
dredged material
sand for sandblasting
Natural vectors are those on which humans have little or no influence; they have
been present throughout history and account for the slow but geologically important
distribution of species over the earth's surface. These natural dispersal mechanisms
are not likely to be controllable.
Vectors that are part of human systems are potentially more manageable. Of
these, ships, specifically ballast water, are both the most significant and the most
manageable vector for the introduction of new aquatic species. Another highly
manageable vector is also related to shipping; namely the canals through which ships
travel can also serve as corridors for the movement of aquatic species. Recreational
or pleasure boats can unintentionally carry species from one water body to another,
and because this is a widely dispersed vector with the potential for significant human
error, it is only moderately controllable. Other accidental introductions, such as release
of live bait or release of specimens from home aquaria, are also only moderately
controllable. Intentional introductions can be partially managed through more effective
enforcement and through increased public awareness of the potentially disastrous
consequences.
5.2 Management Alternatives
A number of possible management alternatives that might target introduction
vectors are listed below. The list was the result of a brain-storming exercise in which
the constraints of environmental, economic, political and social cost were temporarily
disregarded in order to generate a list of possible options. It is not a list of
recommended actions.
Seal off the Great Lakes basin, preventing all in-coming and out-going
vessel traffic. This would require closing the St. Lawrence Seaway and
other points of entry.
Require inspections of the hull, ballast and cargo of all ships entering and
leaving the Great Lakes, for the presence of exotic species.
Require that the hull, ballast and cargo of all incoming ships be treated to
remove or kill any exotic species that may be present
Re-design ships to minimize the transport of invading species. This could
include designs to minimize organism attachment, as well as to prevent
organism entry into on-board water systems.
Canals
Ban the future construction of canals and other water diversions.
Close existing canals and other water diversions.
41
-------
Require frequent inspections of locks, to monitor for the presence of
exotic species.
Design entry lock disinfection systems, which will likely require some sort
of closed basin retention system.
Replace locks with marine railways, on which boats could be pulled up dry
ramps from one waterbody to the next. This is currently done with
pleasure boats in the Trent-Severn waterway, although this may be
impossible for large vessels. A system for disinfecting ships between
waterbodies could be incorporated.
Install barriers to discourage organism movement through canals. These
could be electrical weirs, sonic barriers or bubble curtains, or even
mechanical barriers if no vessels use the canal/diversion.
Recreation
Require inspections of the hulls and live wells of pleasure craft entering
waterbodies.
Require that the hulls of pleasure craft be treated with biocides or by
scraping before entering waterbodies.
Require that live wells in pleasure craft be drained and dried, or heated, to
destroy any exotic species that might be present.
Restrict pleasure craft access to waterbodies, and require that all incoming
and outgoing craft be disinfected.
* Establish education programs targeting all waterbody users, to increase
awareness of the issue and of ways to minimize the risk, e.g., post notices
in various locations, including the doors of public restroom stalls at day-
use facilities at docks, beaches and launch ramps.
Provide hoses to rinse boats and other aquatic equipment at all marinas,
beaches and other waterfront areas used for recreation.
Accidental
Establish education programs targeting aquaculture facilities and the
points of purchase for bait and pond/aquarium species, to increase
awareness of the dangers and to offer ways to minimize the risk.
Require that fail-safe designs be incorporated into aquaculture facilities, to
minimize the risk of escape.
Ban the use of live bait.
42
-------
Regulate the sale of live bait, to avoid between-lake transfer of bait and
bait water. One method might be to require that bait purchases be
registered, and that the bait bucket and any unused bait be returned to
the point of purchase. A penalty could be levied in cases of non-
compliance, and offenders would be identified through the purchase
registration.
Quarantine incoming bait fish, and aquaculture and aquarium species, to
minimize parasite transfer.
Require that incoming fish for aquaculture be disinfected to kill external
parasites.
Deliberate
Implement better regulations.
Improve enforcement. One method might be to make those responsible
for introducing an exotic species (if they can be identified) pay for the cost
of any necessary control and environmental restoration measures.
Improve communication, both to the public and between regulating
bodies. This type of public education could be facilitated by distributing
fliers at state lines and at national borders.
Standardize regulations across jurisdictions, with respect to which species
may be removed or brought in. This could begin with national standards
(i.e., the same regulations across states), or even global standards.
Ban the commercial sale of exotic species.
Decrease market demand for exotic species.
Information gathering and monitoring are important components of any
prevention program. Useful information might include a list of injurious or potentially
problematic species that should be considered in designing prevention programs. This
would require information exchange on a global scale. Monitoring should be
conducted for compliance as well as for effectiveness, to determine whether 1) people
are abiding by the requirements/regulations, and 2) the measures taken are working.
Bans of various kinds and education programs are most likely to be workable
management approaches. Although some of the bans listed above are unrealistic, the
problem was considered to be sufficiently serious to consider the bans. Education
programs, however, are relatively easy to implement and can be started immediately.
43
-------
5.3 Evaluation of Management Options
Three of the management alternatives listed above were evaluated according to
whether they were advantageous or disadvantageous from an environmental,
economic, social, and political perspective. These options were chosen because they
target the most important and manageable introduction vectors. They are not meant
to be interpreted as our preference or recommendation.
Closing Boat Access into and out of the Great Lakes
Closing access to the Great Lakes would be beneficial from an environmental
perspective. Closure would mean fewer spills and less dumping of waste from ships,
and there would be a reduced need for dredging in the lakes. A disadvantage would
be the probable switch to ground transport (trucks, rail) which increases air pollution
and fuel consumption. It is also likely that such a measure would only displace the
threat of new introductions from the Great Lakes to other areas.
From an economic perspective, this measure would probably benefit the rail,
trucking and air cargo industries, but would also increase the need for road and rail
maintenance. The cost of decommissioning the St. Lawrence Seaway and other entry
points would be substantial, and the shipping industry as well as harbor facilities in the
area would be devastated; these industries would be forced to move or shut down.
The social effects would encompass the displacement of workers from the
shipping and harbor industries into ground transport industries. Tourism might benefit
from a more favorable environment for recreational activity and the improved aesthetic
value of the area, but would suffer the loss of tourists who visit locks to watch the
boats go through.
Although this measure could be highly effective, it is unlikely that any Great
Lakes area politician would support such drastic action. There might, however, be
regional support in areas that could benefit from the shift in transportation mode.
Inspections of Ship Hulls, Ballast, and Cargo
This measure would be environmentally and socially neutral. It would be hard to
enforce, and therefore from an economic perspective it would be resource-intensive. It
would likely cause delays to incoming vessels. It would, however, provide the teeth
with which to enforce treatment requirements. Politically, such a measure could be
viewed as favorable because it is cautious and relatively non-disruptive. This measure
could be very effective in the Great Lakes.
Treatment of Hull. Cargo, and Ballast
The subgroup did not have the necessary information or expertise to evaluate
different treatment options, as the environmental, economic, social and political
implications would be treatment-specific. In general, however, the subgroup
recognized that the use of toxic substances could have negative environmental and
social effects, but that treatment measures could be politically favorable because once
the technology is available it would be a relatively quick solution.
The location of the ship when ballast treatment is performed is important;
different countries have different laws for chemical use. If global standards cannot be
44
-------
developed for the use of biocides or other treatment methods, this issue should be
taken into account.
Evaluation Criteria
The subgroup agreed that future evaluation criteria for any prevention measure
should consider:
1) the costs and benefits of implementing that measure;
2) the cost of not implementing that measure; and
3) the effectiveness of that measure with respect to
a) the goal of the prevention program, and
b) other alternatives.
45
-------
INTRODUCED SPECIES WORKSHOP
Saginaw Valley University Theater
September 26,1990
MORNING SCHEDULE
SOURCES, PREVENTION AND MANAGEMENT
J. David Yount, Organizer and Moderator
8:15 Welcome
Erich Bretthauer - Assistant Administrator for Research & Development,
USEPA
BIOLOGY AND ECOLOGY
8:30 Ecology of introduced fishes and aquatic invertebrates in North America
Peter Moyle - Department of Wildlife and Fisheries Biology
University of California, Davis
9:00 Ecology of the Ruffe (Gymnocephalus cernuus) in Europe
Craig Sandgren - Center for Great Lakes Studies, Milwaukee, Wl
John Lehman - University of Michigan Department of Biology, Ann Arbor
9:30 Ecology of the Cladoceran Bythothephes cederstroemi (spinywater flea
or "BC") in the Laurentian Great Lakes.
10:00 Break
10:15 Invasive introduced plant species in the Great Lakes
Tony Reznicek, University of Michigan Herbarium, Ann Arbor, Ml
10:45 Biology & ecology of Dreissena polymorpha from the European USSR
N.F. Smirnova - Institute for the Biology of Inland Water Bodies, USSR
11:15 Ecology and Use of Zebra Mussels in the Netherlands (Europe)
Henk Smit, Institute for Inland Water Management, Dordrecht, the
Netherlands
11:45 Zebra Mussel biology and ecology in North America
Gerry Mackie - Department of Zoology, University of Guelph, Guelph,
Ontario
-------
INTRODUCED SPECIES WORKSHOP
Saginaw Valley University Theater
September 26,1990
AFTERNOON SCHEDULE
SOURCES, PREVENTION AND MANAGEMENT
J. David Yount, Organizer and Moderator
1:30 Species invasions in the Great Lakes: Historical Trends and Entry
Vectors.
Ed Mills - Cornell University, Biological Field Station, Wheatley, Ontario
Joe Leach - Ministry of Natural Resources, Lake Erie Fisheries Station,
Wheatley, Ontario
2:00 Preventing introductions of species into the Great Lakes via shipping
Lt. Cmdr. Randy Helland - U.S. Coast Guard, Washington, DC
2:15 Ship ballast water designs to kill organisms before discharge
Jack Woodward - University of Michigan, Department of Naval
Architecture and Marine Engineering, Ann Arbor
2:45 Break
3:00 Strategy for controlling the Dreissena population in North America.
V.N. Karnaukhov - Institute of Biophysics, USSR Academy of Sciences
3:30 The Zebra Mussel: Chemical and physical control methods for industry
Donald Lewis - Aquatic Sciences, Inc., Ontario, Canada
4:00 Successful management of an introduced species. Sea Lamprey: past,
present and future control species.
Terry Morse - US Fish & Wildlife Service, Marquette Biological Station
4:30 Questions and comments from the audience
-------
ECOLOGY OF INTRODUCED FISHES AND AQUATIC INVERTEBRATES IN NORTH
AMERICA.
Peter B. Moyle, Department of Wildlife and Fisheries Biology, University of California,
Davis, Davis, CA 95616.
The introduced aquatic organisms in the Great Lakes have received a great
deal of attention, but they are only one of the most visible parts of a worldwide
phenomenon of species introductions. I will discuss the problem of introduced
species in North America by addressing four questions:
1. What is the extent of introduction of aquatic organisms in North America?
2. What has been the impact of these introductions on native species and
ecosystems?
3. What allows introduced aquatic organisms to become established?
4. Do introduced species fill vacant niches?
Extent of introductions. Introduced aquatic organisms are found throughout
North America, although some regions have a higher percentage of introduced fauna
than others. The southwestern United States has particularly large numbers; in
California, for example, 48 of 137 freshwater fish species have been introduced. Other
freshwater regions with large numbers of introductions are the Great Lakes, drainages
of the Eastern Seaboard, and freshwaters of Florida. Some organisms brought in from
abroad, such as common carp and Corbicula clams, are found in suitable habitats
throughout the continent, while many North American species, such as green sunfish
and opossum shrimp, have had their ranges greatly expanded. Most successful
introductions quickly expand their populations far beyond the water into which they
were introduced. The inland silverside, for example, spread from Clear Lake in
northern California (where it was introduced for insect control) to reservoirs in
southern California in less than 20 years, becoming one of the most abundant fish
species in the state.
Prior to 1970 or so, most aquatic introductions were made deliberately, often to
improve fishing. For the past 100 years there has also been a steady stream of
accidental introductions as organisms have moved through canals or hitched rides in
or on ships. In recent years, however, there has been a dramatic rise in the number
of introductions, either accidental (e.g. via ballast water) or unauthorized (e.g. via bait
buckets or aquaria). This coincides with major changes in transportation systems
combined with major ecological changes in inland waters and in the Great Lakes or
the Sacramento-San Joaquin estuary.
Impact of introductions. To succeed, an introduced species almost always has
to change the environment into which it is introduced, most commonly by reducing the
1
-------
numbers of native organisms. For example, 24 of the 48 fish species introduced into
California have documented negative effects on native fishes, 22 have not been
studied enough to document effects (or lack of them) and 2 are known to be benign
(but have very limited distributions). In the Sacramento-San Joaquin estuary, two
introduced species of copepod appear to be displacing the dominant native species,
and both of the new species are less vulnerable to predation by larval fish than the
native species. Also, in the estuary, a recently introduced species of clam has
become enormously abundant and may be causing (through efficient filtration) the
record low numbers of phytoplankton observed with consequent reduction of
zooplankton. This species is quite likely causing major parts of the estuary to shift
from planktonic to benthic food webs. The estuary is already highly disturbed, and
about half the fish species are not native, including a small oriental goby which has
become very abundant in the past four years.
Characteristics of successful introduced species. Successful introduced
species usually have several of the following characteristics: (1) They are hardy, thus
can survive transport under adverse conditions. (2) They are aggressive, either
behaviorally or physiologically, thus can displace native organisms. (3) They have
reproductive strategies that allow them to expand their populations rapidly. (4) They
have the ability to disperse rapidly. These characteristics are especially helpful when
the species invades an environment that is highly disturbed by human activities. Thus
44 of the 48 introduced fishes in California thrive primarily in disturbed environments.
Vacant Niches. This concept is brought up because it is used so frequently to
justify an introduction or to 'excuse1 one that has already been made. Basically,
niches cannot be "vacant" because they are characteristic of the organism, not the
environment. Therefore, an invading species carries its niche with it and almost
always displaces or shrinks the niche of another species (or many others) when it
invades. Introduced species often appear to have no effect because the time frames
of studies are too short or researchers do not study the appropriate native species
(e.g., clams can compete with larval fish for food).
Understanding the effects of introduced species, regulating these effects, and
preventing further introductions into aquatic systems are important activities for many
reasons. Perhaps the most important, however, is that introduced species are
contributing in a major way to the worldwide loss of biodiversity.
References
Herbold, B. and P.B. Moyle. 1986. Introduced species and vacant niches. American
Naturalist 128:751-760.
Moyle, P.B. 1986. Fish introductions into North America: Patterns and ecological
impact. Pages 27-43 JD H.A. Mooney and J.A. Drake (eds). Ecology and
biological invasions of North America and Hawaii. Springer-Valag, N.Y.
-------
Moyle, P.B., H.W. Li and B.A. Barton. 1986. The Frankenstein effect: Impact of
introduced fishes on native fishes in North America. Pages 415-416 jn R.W.
Stroud (ed). Fish culture in fisheries management. American Fish. Soc.
Bethesda, MD.
Moyle, P.B. and R.A. Leidy. 1990. Loss of biodiversity in aquatic ecosystems:
Evidence from fish faunas. Jn P.L Fiedler and S.A. Jain (eds). Conservation
Biology: The theory and practice of nature conservation, preservation, and
management. Chapman and Bell N.Y. (in press).
-------
ECOLOGY OF THE RUFFE GYMNOCEPHALUS CERNUA (LINNAEUS 1758) IN
EUROPE.
Peter S. Maitland, Fish Conservation Centre, Easter Cringate, Stirling, Scotland.
The Ruffe (sometimes called the Pope) is a small member of the perch family.
Ruffe are found in lakes, slow flowing rivers and canals throughout northern Europe
and across central and northern Asia. It is a recent introduction to North America.
The species also occurs in the low salinity areas of the Baltic Sea where it reaches its
maximum size of 45-50 cm and about 750 gm. Elsewhere, it seldom reaches more
than 20 cm, except in a few favorable habitats.
In the British Isles it is indigenous to eastern and southeastern England and is
common locally, but it has been redistributed to some extent by canal networks within
the English midlands and has now reached the lower Severn and Welsh Dee systems.
It is absent from Ireland, and was absent from Scotland until very recently when it
became established in Loch Lomond, evidently brought in as bait by Pike anglers. It
has also appeared recently in southwest Scotland in Loch Ken.
Gonad development and sexual maturation are temperature dependent.
Spawning takes place from March to May, when shoals of Ruffe move into shallow
water. The spawning migration starts at some 4°C and spawning itself can occur at 6-
8°C, although the normal range is 11-18°C. The eggs are yellowish white in color (the
yolk sac contains a large oil globule) and 0.5-1.0 mm in diameter. Each female can
produce 4,000-100,000 eggs depending on her size, but spawning is sometimes
intermittent and the eggs may be laid in one or more batches. The adhesive eggs are
deposited individually, sticking to stones and vegetation. The eggs hatch in some 8-
12 days when water temperatures are between 10 and 15°C.
In some ways, Ruffe are very similar to Perch; indeed the two species can
hybridize and this appears to occur naturally in some parts of the River Danube. The
progeny, however, are sterile. In general, the range of the Ruffe is more northerly
than that of the Perch, and one author has referred to it as an "Arctic Perch." Ruffe
have a lower oxygen requirement than Perch and are thus able to occupy habitats
where Perch would be under stress (e.g. mildly polluted waters).
Newly hatched fry are transparent and 3-4 mm in length. By the end of the first
year they may reach 3-6 cm, and 7-9 cm by the end of the second year. Growth then
seems to slow and by the time they are four years of age they may only be around 10
cm. In many waters, very few Ruffe seem to live beyond five years of age. They
mature at an early age - males in their first or second years and females in their
second or third years.
-------
Ruffe are gregarious fish, often feeding in shoals - though these are rarely as
large as some Perch shoals. Usually they feed actively during the day, with a peak
towards dusk. At night Ruffe lie concealed on the bottom. They are exclusively
carnivorous, feeding on bottom-living invertebrates, especially mollusks, crustaceans
and insect larvae (notably midge larvae, which form a significant proportion of their
diet). They take approximately the same range of organisms as Perch, but because
they are more benthic in habit than Perch, Ruffe appear to take a greater proportion of
mud dwelling invertebrates. They also take fish eggs (e.g. of Smelt Osmerus
eperlanus) and small fish, and it has been shown in some large Russian lakes that
where Ruffe and whitefish (Coregonus) occur together, the Ruffe exert a significant
control over the production of whitefish because of the enormous number of whitefish
eggs which they consume. Unlike Perch, they feed throughout the winter but at a
reduced level.
Ruffe have several natural predators and in some waters form an important item
in the diet of Pike (Esox lucius). Pikeperch (Stizostedion lucioperca) and Burbot (Lota
lota). The species is also eaten by piscivorous birds. Ruffe also have a number of
parasites including various Cestoda, Trematoda and Nematoda.
Ruffe are easily caught by angling with bait such as maggots or worms, but
they are not considered to be an important sport fish. The present British rod-caught
record is for a fish of 148 gm caught in 1980 in a pond at West View Farm in Cumbria.
Often, small Ruffe and small Perch may be caught at the same time at the same spot.
Many anglers consider them to be a great nuisance, taking the bait before a more
acceptable species can get to it. As a dead bait they are favored by Pike anglers.
Their flesh is well flavored, like that of Perch, and there was originally an extensive
fishery for Ruffe in the lagoons of the Baltic Sea. This has declined greatly in recent
years owing to lack of demand.
Studies of the ecology of the new population of Ruffe in Loch Lomond, first
detected in 1982, have indicated an enormous increase in population size. Numbers
taken on the intake screens of a water supply facility have increased from nil in 1981
and 17 in 1982 (8.1% of the catch) to 1280 in 1987 and 3015 in 1988 (91.6 and 88.9%
of the catch). The species is now very widespread through the whole of Loch
Lomond (71km2) and its major inflow and outflow. The biology is similar to that
reported in other waters, though in the early 1980's only a few year classes (0-4 + )
were caught. Growth is variable but most fish reach 7-9 cm by the end of their
second year and 9-11 cm by the end of their fourth year. Spawning occurs in April
and May. The main food is aquatic benthic invertebrates, but eggs of the Powan
Coregonus lavaretus (occurring in only two lochs in Scotland) are eaten extensively in
winter when Ruffe are still very active. Ruffe now form an important part of the diet of
Pike in Loch Lomond.
-------
ECOLOGY OF THE CLADOCERAN BYTHOTREPHES CEDERSTROEMII (spiny water
flea or "BC") IN THE LAURENTIAN GREAT LAKES.
Craig D. Sandgren, Center for Great Lakes Studies, University of Wisconsin-
Milwaukee, and John T. Lehman, Department of Biology, University of Michigan.
Bythotrephes cederstroemii is a predatory zooplankter that has recently invaded
the Great Lakes region. Bythotrephes is morphologically distinctive, having a large
protruding pigmented eye, an enlarged dorsal brood sac, and a very long caudal
spine. The animal is very large for a zooplankter, and is easily seen with the naked
eye; total length of adults can be as great as 13-15 millimeters including the spine. It
was first reported in southern Lake Huron in December 1984, and subsequently
spread east to Lakes Erie and Ontario in 1985, west into Lake Michigan in late
summer 1986, and into Lake Superior in 1987. It seems most probable that this
animal entered the Great Lakes system via ballast water from ships frequenting
European ports with low salinity harbors. Bythotrephes is native to lakes in Europe
and the western Soviet Union, where it is typically a minor component of the
planktonic invertebrate assemblage and has been little studied.
Each Laurentian Great Lake has responded to Bythotrephes in a different
manner, probably as a result of their different fish communities since planktivorous fish
can act as predators on Bythotrephes. The most dramatic response and probably the
best studied invasion sequence has been in Lake Michigan. The information reported
here is a summary of the basic biology of this animal and its impact on the Lake
Michigan food web, as documented over the last four years.
The reproductive biology, seasonal population cycle, and distribution pattern of
Bythotrephes within Lake Michigan are the subjects of intense current research efforts.
The annual cycle of population development is generally similar to native cladoceran
crustaceans. The first animals entering the plankton are females recruited from
sedimentary resting eggs in early summer. Summer populations result from repeated
cycles of asexual or parthenogenetic reproduction by females. They produce from 4-
12 embryos in a brood; the neonates are subsequently released with well-formed
spines. Development rates are strongly dependent on temperature; the reproductive
cycle from mature female to a new mature female is estimated to require as little as 10
days under optimal conditions. Maximum population abundances occur in late July
and August, and have been estimated to be as high as 1,000 animals per square
meter of lake surface.
Bythothrephes populations are usually restricted to the epilimnion and upper
metalimnion; they do not exhibit strong or consistent diurnal vertical migration
patterns. Abundances are generally higher offshore than in shallow water, but the
horizontal distribution appears to be very patchy and local areas of very high
nearshore abundances have been reported by fishermen. Populations become food
1
-------
limited at times during the summer, inducing a switch to sexual reproduction, the
production of resting eggs, and a decline in numerical abundance. Sediments of Lake
Michigan have been estimated to now contain as many as 10,000-50,000 resting eggs
per square meter.
The Bythotrephes invasion has resulted in many biological changes throughout
the Lake Michigan food web. The most profound changes have concerned the
structure of the zooplankton community. In Europe, Bythotrephes is reported to feed
on diverse size classes of herbivorous zooplankton; however in Lake Michigan it
appears to have specialized on species of Daphnia. the dominant herbivores in the
system. Daphnia abundances declined drastically in 1987. Subsequently, the
helmeted species D. galeata-mendotae has been able to coexist in the presence of
Bythotrephes but the smaller species, J3. retrocurva and the unhelmeted D. pulicaria
have been severely reduced in abundance compared with pre-invasion levels.
Associated with the Bythotrephes invasion of Lake Michigan has been a decline in
recruitment success of the bloater chub (Coregonus hoyi). the dominant pianktivorous
fish in the offshore region and an increasingly important food item in the diet of the
lake's highly managed salmon populations. Bythotrephes may be successfully out-
competing young-of-the-year bloaters for the same food resource - Daphnia.
Bythotrephes may thus be serving as a food web "bottleneck", diverting resources
from the managed fishery. The native zooplankton community has also been
impacted. Leptodora kindti, a native predatory cladoceran, has declined in
importance, and two of its primary food items, the colonial rotifer Conochilus unicornus
and the small herbivorous cladoceran Bosmina longirostris. have subsequently
increased in abundance. Other small zooplankters have also increased in importance,
perhaps signalling a shift to a generally smaller-bodied zooplankton assemblage as
Daphnia has declined. The phytoplankton community has also responded, but in
unsuspected ways. Despite the dramatic changes in the herbivorous zooplankton
assemblage, the algal biomass (as chlorophyll), size distribution and dominant species
have remained unchanged. There has, however, been an apparent increase in
biomass-specific production and potential growth rates of the dominant small-sized
algae. It is unclear at this point where this additional production is going, but it does
not appear to be entering the traditional large zooplankton-to-fish food chain.
All these changes may be influencing the flux of carbon and energy through the
food web in such a manner that the future may require fundamental changes in
fisheries management practices and a reevaluation of realistic sport fishing
expectations. Unlike the zebra mussel invasion, where economic impact can be
measured in terms of direct costs to clean up mussel-fouled water intake systems, an
assessment of the economic impact of Bythotrephes must wait until a clear fisheries
response to the fundamental and complex food web alterations of the last few years
can be ascertained.
-------
INVASIVE INTRODUCED PLANT SPECIES IN THE GREAT LAKES.
A.A. Reznicek, University of Michigan Herbarium, Ann Arbor, Michigan.
Invasive plant species of Great Lakes wetlands and aquatic systems form a
complex topic. There is no such thing as an intrinsically invasive species. Many of
the worst pests in the Great Lakes region are rare plants in parts of their native range.
There are species, however, both native and introduced, that find conditions at a
certain point suitable for their spread. Although this means that one cannot fully
understand invasive species without a full environmental context, such a context is
beyond the scope of this abstract.
Introduced species are also not intrinsically harmful. In eastern North America,
about 20% of the flora is introduced. Most of these species are rare waifs, and most
are terrestrial. In western Lake Erie, the most affected portion of the Great Lakes,
about 10% of the flora is introduced. Other areas of the Great Lakes (with a total
wetland flora of about 450 species) would have a somewhat lower percentage.
Considering the excellent dispersability of aquatic organisms, this is not high. Of these
introduced species, most are ruderals and merely facultative aquatics, or else are rare
and strong competitors. However, the percentages do not reflect the communities in
western Lake Erie, and many wetland communities elsewhere in the Great Lakes are
dominated by introduced species.
The following plants, listed with annotations, are the major species of invasive
plants in the Great Lakes, based on current knowledge, with comments on the timing
of their spread, if available, and their actual or potential impact, as far as is known.
Purple loosestrife, Lythrum salicaria. is the best documented invasive introduced
species, and the one with the greatest pest potential. It is an extremely good
competitor with a tremendous seed bank of up to 21,000 seeds per m , which makes
control very difficult. Although purple loosestrife has been in the Great Lakes region
since the 1880's, extensive spread to become a severe pest has been much more
recent. Nevertheless, purple loosestrife has been recognized locally as a problem by
botanists since the 1930's. Purple loosestrife has a severe impact on wetlands. It is
unpalatable, therefore of little value as wildlife food, and crowds out other vegetation,
sharply reducing diversity.
Hybrid cattail, Typha x glauca. is poorly documented in terms of overall
occurrence, but extensively studied from the viewpoint of systematics and ecology. It
is a hybrid of the native X- latifolia and X anqustifolia. introduced from the east coast
of North America. The hybrid is now widespread and is an extremely strong
competitor. It is much more tolerant of salt and other pollutants, because the X
angustifolia parent is a salt marsh species and, with hybrid vigor, is more able to take
-------
advantage of excess nutrients. The impact of hybrid cattail is as an extremely strong
competitor able to generate monodominant, low diversity vegetation.
Common reed, Phragmites australis. is native to the Great Lakes region
generally, but was almost certainly rare and sporadic in Great Lakes wetlands in pre-
settlement times. It is a very recent rapid invader, having become abundant since
about 1970. The species is a very strong competitor, able to spread vegetatively with
tremendous rapidity by stolons up to 30 m long, as well as by rhizomes. It is very salt
and pollution tolerant, and has also spread along heavily salted roadsides, especially
expressways, as well as wetlands. It forms extremely dense monodominant stands of
unpalatable vegetation, greatly decreasing diversity of wetlands.
Frog's bit, Hydrocharis morsus-ranae. is probably the most recent potentially
serious invader, having entered North American wetlands as recently as 1939, and the
Great Lakes substantially later. Frog's bit is now present in Lakes Ontario and Erie. It
is a free-floating aquatic that forms monodominant stands not limited by water depth.
Its full impact is unknown, but potentially severe. The absolute coverage of the water
surface in areas where it is abundant substantially reduces submerged aquatic species
and may even suppress emergents.
Eurasian water milfoil, Myriophyllum spicatum. is another well-studied invader. It
was recognized late due to confusion with native species and is somewhat poorly
collected, but is evidently a recent spreader. It is now present in all the Great Lakes
but is only locally a problem. It is most likely an opportunistic species that will invade
holes under optimal conditions. Although a submerged aquatic, since it branches
close to the water surface, it is able to grow in turbid water, as well as to shade out
other submerged aquatics if any are present. Fruit production is low, so the species is
less valuable as wildlife food than the plants it displaces.
Curly-leaved pondweed, Potamogeton crispus. is another well-studied species.
It has long been present in the Great Lakes, but has only relatively recently been a
major invader of wetlands. It is only a local problem, and like Eurasian water milfoil is
a surface brancher able to grow in turbid water and displace other species if any are
present. Also like Eurasian water milfoil, it is an opportunistic species that probably
invades areas where other species have been eliminated. Its impact is probably low,
but it can shade out submerged aquatics and reduce diversity of wetlands. Fruit
production is low, so it has only modest value to wildlife.
Additional presently-minor introduced species that may cause problems locally
or may spread in the future are reed canary grass (Phalaris arundinacea). slender
naiad (Najas minor), small-flowered willow herb (Epilobium parviflorum). and flowering
rush (Butomus umbellatus).
-------
In the most basic terms, the reason that introduced species are a problem is
because the ecosystem has been perturbed, and is responding with the resources
available to it, which includes introduced species and genotypes. This may sound
trivial, but is an essential concept since it mandates ecosystem-based solutions to the
problem of introduced species if any solutions are possible. Past responses to
introduced aquatic weed problems have typically been at the level of "this is a bad
plant, we must kill it", hardly an ecosystem approach and one reminiscent of the
discredited concept that predators are bad and must be killed. In all cases, when
dealing with introduced species, it is essential to try to understand the system before
taking action.
Weed problems in the Great Lakes are, on a broad scale, due to the interplay
of three classes of environmental parameters: turbidity, nutrient levels, and the
competitive ability of participating species under existing conditions. All three of these
factors are complex and other variables may also play a role locally, including levels of
non-nutrient pollutants and marsh management schemes. Fundamentally, turbidity
reduces the depth to which aquatic species can grow. This is most serious, since it
greatly reduces the area that macrophytes can occupy on a lake bottom. It also gives
an advantage to species such as Eurasian water milfoil, elodea, curly-leaved
pondweed, sago pondweed, and coontail, which are surface branching submerged
macrophytes; as well as floating-leaved and entirely floating species. The effect of
nutrients is largely to provide a few very good competitors with sufficient nutrients that
they can completely dominate sites. These species can be either native or introduced,
and are simply showing a natural response to altered ecosystem parameters.
Competitive ability then is a predictor of those species that are likely to become
serious pests if nutrients become available in excess.
Solutions to the problem of invading introduced species are, in the long run, to
improve water quality in the Great Lakes, especially decreasing nutrient loading and
turbidity, and to ensure the natural water level cycling and concomitant flushing and
rejuvenation of shoreline wetlands. Little can be done in the short term, although
physical removal of the offending biomass is as effective as anything on a local scale,
and at least removes nutrients from the system. Attempts to simply kill the offending
species do nothing to ameliorate the basic causes of the problems. In this light, the
tremendous filtering ability of the zebra mussel may be of benefit to aquatic
macrophytes.
-------
BIOLOGY AND ECOLOGY OF DREISSENA POLYMORPHA FROM THE EUROPEAN
USSR
N. Smirnova, Institute of the Biology of Inland Waters, USSR Academy of Sciences,
Borok, USSR
Dreissena was first found in the lower course of the Ural river in 1769 by a
famous traveller and well-known Russian zoologist Piter Pallas. As a zoological
species Dreissena polymorpha (Pallas) was described by him in 1771. Dreissena
became of great interest during the third decade of the 19th century when it was
found in London docks, in Kurishgaf, and then in different places of Western Europe.
In Germany, it acquired the name of wandering mussel ("Wundermuschel"). A little
later, alarm signals appeared when this mollusc blocked pipes and spoiled water in the
water supply system of Budapest (1878), Hamburg (1886), Paris and Arli (1893), Berlin
(1895), and many other towns in Europe.
In the USSR., many water pipes, hydrotechnical structures, and ships suffer
from Dreissena. It would be erroneous, however, to consider Dreissena as only a
menace in the economy. It is undoubtedly useful as an effective freshwater filtrator,
which forms a powerful filtratory belt, improving the water quality (Stenczykowska,
1968; Lvova-Kachanova, 1971; Lvova, 1977). This ability of Dreissena is just
becoming necessary in connection with increasing anthropogenic eutrophication and
water pollution, especially if the water is used for drinking or technical purposes.
In addition, Dreissena serves as a food for some commercial fish species
(Vorobyev, 1949; Kondratiev, 1958; Yablonskaya, 1975). A rapid dispersal of
Dreissena is facilitated by its biological peculiarities.
Dreissena is a dioecious organism. Fertilization occurs in the external water,
which is associated with a high absolute fecundity. The gonad weight makes up 10.0-
17.0% of the total wet weight in females and 4.0-12.0% in males (Spiridonov, 1971).
The mollusks rapidly attain maturity. Mature individuals occur among 6mm long males
and 7mm long females; all Dreissenas 10mm long are mature.
The trochophor, 60-70 microns in size, develops from the egg. The larva is
termed veliger from the moment of shell formation until attachment to a substrate. The
veliger floats in the water with the help of a velum. The organs of digestion, blood
circulation, excretion and others develop in it. Boundaries between separate periods
of growth become visible on the veliger's shell. The veliger dimensions are 250-255
microns. In the water-bodies of the European USSR, the larvae stay in the plankton
for 7-10 days according to many authors (Kirpichenko, 1965; Skalskaya, 1976;
Karataev, 1983; and others).
-------
The veliger which settles on a substratum quickly develops into a postveliger
having a long and powerful foot. The foot has a deep slit-like pit on the sole, which
helps the mollusc to be firmly attached to the substratum and to glide even on the
water surface tension film. The postveligers are from 250 to 700 microns in size. The
growth and development of postveligers are manifested externally in changes of the
shell shape and size. The settling veliger has a symmetric round shell. Then the shell
begins to elongate and grow asymmetrically, acquiring a triangular shape. The
branchial and anal syphons appear (syphon forming stage, Kirpichenko, 1965). After
some time, the mollusc excretes from the foot sole thin threads of mucus, which, on
solidifying in water, form the so-called bissus, firmly attaching the mollusc to the
substratum (definitive stage).
During conversion of the larva from the veliger to the definitive stage, about four
lines of growth are formed on the Dreissena shell. Further formation of the growth
lines and rings on the shell is conditioned by various other causes: wintering, episodic
deterioration of environmental conditions (oxygen deficiency, sudden drop in
temperature, etc.), when the animal's growth temporarily ceases or slows down. It
has been noted that a distinct growth line is formed even if the animal slightly dries up.
In this case, the shell becomes teratic with a sharp line. A rather distinct line on the
shell is also formed after egg laying, since the mollusc does not grow during
spawning, accumulating nutrient substances for sexual products.
The maximal size of the adult mollusc may reach 40mm. The Caspian and Aral
Dreissenas are significantly smaller than the river and lake forms. Large Dreissenas
are almost incapable of moving by themselves. Only extremely adverse conditions
make adult Dreissenas leave their bissus and move slowly from one place to another.
It is the pelagic larva, which may be carried over great distances by the current, and
the bissus, which helps the mollusc to attach itself to ships, rafts, water fowl, fishing
gear, and some aquatic organisms, that secure successful spreading of Dreissena
over water systems.
Spawning is very much prolonged due to gradual ripening of the sexual
products and occurs at a temperature of 15-17° C (Kirpichenko, 1965; Spiridonov,
1971; Karataev, 1983). It ends at 11° C. During spawning, two peaks of veliger
abundance are clearly seen in July and August, which may shift in time depending on
conditions.
Under favorable conditions, the veligers play a dominant role in the number and
production of the zooplankton (Karataev, 1983). During the great peak, the number of
larvae in the water may reach 40 to 400 thousand individuals per cubic meter
(Kirpichenko, 1965; Spiridonov, 1971).
Growth of Dreissena after wintering starts at 10-11° C. With increases in
temperature, the specific growth rate of postveligers increases. Some observations on
-------
cooler waters, where the temperature in the littoral is four degrees and in the profundal
1-2 degrees higher than in naturally heated waters, are of interest (Karataev, 1983).
The density of larvae has been shown to be higher in a zone with a natural thermal
regime. Thus in Lake Lukomlskoe (B.S.S.R.), the mean seasonal number was 2.5
times and biomass was three times as great as that in the unheated zone of the lake.
The larvae develop better in the upper layers of water to a depth of 10m. Diurnal
migrations of the larvae also occur. The maximal concentration of the larvae is
observed near the surface at night, and at a depth of 3m in the daytime. The
Dreissena veligers have been shown to be more resistant to adverse environmental
conditions than the adult organisms. It was found, that the adults were absent in the
zone polluted by waste waters of food and metallurgical industry, while the larvae
numbered more than 1,000 individuals per cubic meter in the plankton (Dyga, 1966).
Being very resistant to unfavorable environmental conditions, the Dreissena
larvae are at the same time very sensitive even to the slightest changes in
environmental conditions, which is manifested in its development, growth and
abundance. This sensitivity is one of the essential features of its adaptation and allows
the organism to prepare to withstand more adverse oncoming conditions.
Fluctuations of the water level play a great role in the life of the veligers, since in
winter they influence mortality in the littoral Dreissena populations due to freezing, and
in summer, they determine the character of the relationship between populations of the
protected inshore zone and of the open water, which facilitates enriching of the
genofund and leads to flourishing of the species (Skalskaya, 1987).
Some authors have shown that natural fluctuations of the abundance occur. In
the Dnepropetrovsk reservoir each third year was a bad harvest (Dyga, 1966). In the
Kyibyshevsk reservoir it was bad each fourth year (Kirpichenko, 1964). The periodicity
in Dreissena reproduction is a regularity, not the same for different waters.
During the first stages after settling in new areas, Dreissena occurs at all
depths, then it forms aggregations in places rich in suspended food and having a
favorable hydrochemical regime. Dreissena inhabits mostly eutrophic and mesotrophic
lakes. In lakes, it prefers silted sands and occurs in least numbers on liquid muds of
the profundal zone.
In reservoirs, very high numbers are observed on stony substrates, and
insignificant numbers are found on muds, silted sand and clay. The quality of the
substrate influences the number of mollusks if the colonies settle directly on that
substrate. Dreissena does not inhabit pure sandy substrates and places with a great
amount of mud and no current. It is especially numerous on flooded forest, bushes,
stumps and snags.
-------
For Dreissena. the oxygen demand of the water and its hardness are very
important. It is known from observations in nature that Dreissenas do not occur in
waters rich in organic matter of humic character (with high oxygen demand).
It is also known that it does not live in low salt (soft) waters. There is no
Dreissena. for instance, in Lake Ladoga having very low water hardness, in spite of a
possibility of Dreissena immigration from Lake llmen. This mollusc resists high salt
content in the water much better. Dreissenas resist well low sodium and chloride
content, but not low calcium and magnesium sulfates. The main reason for this is the
salt content of the Caspian water, from which Dreissena originated.
Both the larvae and adult organisms are filter feeders. They deal with a great
amount of suspension and sort out the seston into edible and non-edible fractions.
The branchial and anal syphons take an active part in this. The branchial syphon
serves as a filter in preliminary purification of water from coarse suspension. Fine
suspension particles pass freely through the net of tentacles of the branchial syphon.
Then in the posterior part of the mantle cavity one more sorting of the suspension into
edible and non-edible components takes place. The unusable part of the suspension
is removed from the mantle cavity in the form of agglutinates.
By the character of feeding Dreissena is a clear detritivore (Mikheev, 1966,
1967). Detritus makes up more than 90% of the total food; the remaining 10% is
plankton represented by small phyto and zooplankton.
Food consumption increases with increase in the mollusc size. In the
Kuibyshevsk reservoir detritus is the sole food for Dreissena less than 1mm in size.
The mollusks 2-3mm long feed on the protococc and diatom algae in addition to
detritus. In Dreissenas of average size, the phytoplankton food is represented by the
blue-green, diatom, green and peridinium algae. They do not feed on zooplankton,
however. Only large individuals are capable of feeding on zooplankton, mostly rotifers
and Dreissena veligers. An increase in the food diversity during Dreissena growth is
associated with the increase in the water filtration rate.
The water temperature from 15-17 to 23-24° C is optimal for feeding of
Dreissena. and therefore, for its living activity. At 30° C., Dreissenas filter water very
unevenly. This temperature is very close to the upper temperature limit equal to 32-
33° C. Temperature below 3° C is unfavorable for Dreissena.
The filtration rate depends on seston concentration in the water. The mollusks
filter most effectively at a low suspension concentration. With an increase in
suspension content in the water almost the same amount of suspension is consumed
for feeding as at low content, but the ability of the mollusks to flocculate seston greatly
increases.
-------
Oxygen regime in the water-body greatly influences the feeding rate. An
oxygen saturation of 80-85% is optimal. At a decrease in oxygen content, Dreissena
excretes 3-5 times smaller amounts of metabolites than under optimal conditions.
Current velocities from 0.1 to 1 m/sec are favorable for the living activity of
Dreissena. At velocities greater than 1-1.5 m/sec feeding decreases even though food
is abundant. Very fast water flow deforms the mollusc's syphon protruded from the
shell, and if the seston concentration is low, the mollusks suffer from hunger.
It is clear from the above that when great masses of Dreissena accumulate in
reservoirs, these mollusks perform a great work of filtering the water and accumulating
metabolites. In the Volgogradskoe reservoir Dreissenas filter on the average two fifths
of the total water volume daily during the summer (Mikheev, 1966). At the same time
the process of sedimentation is accelerated due to formation of agglutinates and feces
in places inhabited by Dreissena.
The water which passed through the filtering apparatus of Dreissena is almost
free of suspension. Therefore, the food resources for zooplankton filtrators are
reduced, and for benthic pelophillic species are improved. Developing on different
substrata, the Dreissena accretions create favorable conditions for phyto-detritovore
filtrators, which make up 90% of the total benthos biomass (without Dreissena). and
for phyto-detritovore filtrators + scavengers (1.6-5.2%)\ An insignificant role is played
in the Dreissena community by omnivorous scavenger-swallowers and predatory
invertebrates.
Thus, at high population levels Dreissena acts as an environment-forming
element, as a biotic factor changing essentially the living conditions for other species.
This results in changes of the trophic structure of aquatic ecosystems.
Ecological, physiological and morphological features of Dreissena are of great
interest. It is well-known that species populating wide areas and adapted to diverse
environmental conditions are able to rather rapidly produce some local, clearly distinct
forms (populations, ecotypes, races). Dreissena is a good example of this. Being one
of the most numerous components of benthic communities and spreading easily along
the Volga channel, which seems to mix up its populations and level them, it has
formed populations different significantly in ecological, physiological and morphological
characteristics. This has been shown in studies of resistance of the mollusc to
changes in temperature and salinity on the whole organism and on the cell level
(thermo- and osmoresistance of the cilated gill epithelium) (Shkorbatov, 1986). The
Tybinsk, Kostroma, Kuibyshev, Samara, Chapaev and Astrahan populations were
studied.
Evidenced by the heat resistance of the whole organism, the Astrahan and
Kostroma populations are clearly the most resistant, those of the Rybinsk and
-------
Kuibyshev area are the least resistant. These differences correspond to environmental
conditions of the compared groups: the Astrahan is the most southern, the Kostroma
inhabits a zone influenced by discharge of heated waste waters from the thermal
power station.
The salt resistance of the mollusc differs even more distinctly. The Astrahan
group, living near the marine part of the species' distribution area, has been shown to
be the most resistant; the least resistant is the Rybinsk group, most distant from the
Caspian sea.
Survival of the ciliated epithelial cells under increased salinity conditions (25 per
mille) is highest in the Astrahan group and lowest in the Rybinsk group.
Oxygen consumption at different salinities differs distinctly, which confirms the
data on general and cell salt resistance.
The characteristics presented here illustrate well the ecological and
physiological differentiation of the species. The differences in the investigated
characters appear quite stable (adaptation to the same conditions has not leveled then
down), and correspond to climatic and environmental conditions of the habitats of the
compared groups.
In addition to ecological and physiological peculiarities some statistically
significant differences have been established in morphology of the compared groups.
The materials provided here show how the symptoms of interspecific
differentiation of Dreissena are diverse and significant within the Volga part of the
species' distribution area, where isolation of separate groups is quite relative. It is
natural that the populations of this species from different more isolated parts of the
distribution area differ to a much greater extent.
Analysis of polymorphism of color and pattern on the Dreissena shells taken
from various parts of the European USSR has revealed four main varieties: dark
stripeless, light stripeless, radial stripped and dentated striped. Distribution of the
occurrence frequency of the varieties of Dreissena distinguishes four main groups: the
Aralo-Caspian, Ponto-Caspian, Middle-Russian, Baltic and the Northeast. They differ in
both the number of the varieties and the ratio of these varieties (phenes). The
maximum number of varieties (all four) and the greatest differences in the ratio of
these phenes are found in the Arab-Caspian group, which is indicative of its unique
position in the system of the inter-specific differentiation of Dreissenas (Biochino,
Slynko, 1988; Biochino, 1990). Since all the groups, in addition to their phenotypical
peculiarities, are bound to certain geographical regions differing in the time of
colonization by Dreissena (Morduhai-Boltovskoi, 1960) and coincide with
zoogeographical division of the Eurasian mammal fauna (Starobogatov, 1970), one
-------
may propose that these groups possess the status of geographical races (Mayer,
1974).
Studies of the geographical variability have shown that the polymorphism
decreases with approach to boundaries of the species distribution area.
To explain the obtained data on ecological, physiological and morphological
peculiarities of Dreissena one should consider the history of its origin, which was first
described by A.I. Andrusov as early as in 1897. The contemporary family of
Dreissenas is represented in the world fauna by only two genera, JDreissena and
Congeria. The most ancient representatives of Dreissena belong to the genus
Congeria. which appeared in the early Eocene. The greatest development of this
genus occurred during the epoch of the 1st and 2nd Pontic tier. In the Pliocene
Congeria almost completely disappeared from Europe replaced by the genus
Dreissena. The maximum development of Dreissena occurred during the Khvalynsk
time of the Quartionary period. During this period, it became widely spread over the
Volga and its tributaries, occupied Northern areas of Eastern Europe, penetrated into
Western Europe and also settled in the Aral sea.
In the Upper Pliocene Dreissena penetrated into the area of Slavonia and at the
beginning of the Quartionary time into Albania. It is worth mentioning that looking at
the map of distribution of the family of Dreissenids, presented by Andrusev (1897) and
supplemented by Zhadin (1946), it is easy to understand why Dreissena polymorpha
was absent in America till recent time.
As has been said already, the time when the genus Congeria appeared in
Europe is ancient Eocene. At that time, according to Wegener's theory (1925) of
continental drift, Europe and Africa were in contact with the American continent and
could have a common fauna or could exchange their faunas. Later, in Pliocene, when
the genus Dreissena differentiated in Europe, Europe had already separated from
America and penetration of a new species there became impossible.
During the Quartionary glacial epoch Dreissena was rapidly displaced from that
huge distribution area which it had occupied in the Khvalynsk time. It was not only
because of climatic conditions; the erosion by glaciers probably affected Dreissena
much more strongly. The waters of the glacial time were saturated with coarse
suspensions, which had an adverse effect on both the adult and larval mollusks. The
disastrous effect of turbid glacial flows could be traced far beyond the glaciers
themselves. On the other hand, favorable oases of clean water might be preserved in
some places, where Dreissena could have survived the glacial time.
Thus, Dreissena survived the glacial epochs not only in the brackish waters of
the Caspian and Aral, in the freshened parts of the Azov and Black sea, but also in
some water-bodies of the Balkan peninsula and Near Asia and, probably, directly in
-------
the area of glaciers. This is confirmed by Dreissena findings in intraglacial deposits in
both East and West Europe. After the glacial phenomena receded and the water in
rivers became clear, Dreissena started to conquer the lost habitats.
At the present time, owing to peculiarities of its biology and to a great
physiological durability, Dreissena rapidly spreads to new areas suitable for its life.
REFERENCES NOT AVAILABLE
8
-------
ECOLOGY AND USE OF ZEBRA MUSSELS IN THE NETHERLANDS (EUROPE).
H. Smit, A. bij de Vaate, H. Reeders, E. van Nes and R. Noordhuis, Inland Institute for
Water Management and Wastewater Treatment, Lelystad, The Netherlands.
The zebra mussel is an indigenous species in Europe, since it was present here
before the last glacial era. Recolonization took place about 160 years ago by
merchant vessels and through the inland waterways.
In the Netherlands, the embankment and subsequent freshening of former
estuaries has created several suitable zebra mussel habitats. From a study in Lake
Volkerak, it is concluded that also in The Netherlands zebra mussels are very rapid
colonizers. A population is gradually built up in two successive years. Release of
oocytes and spermatozoids starts in spring as soon as the water temperature rises
above 12° C. A second release of reproductive materials takes place during summer
at a temperature range of 16-21° C. The veliger larvae settle after 2-3 weeks on solid
substrates. The young mussels may reach maturity the same summer, if
environmental conditions are suitable. A reproduction peak in September is probably
attributable to the young mussels. This means that the zebra mussels may have two
generations annually. Low temperatures during winter induce gonad development.
From the reproductive cycle it can be deduced that zebra mussels are restricted to
water bodies with summer temperatures above 12° C and low water temperatures
during winter.
Zebra mussels tolerate chloride concentrations up to about 600 mg/l. In the
Netherlands, shell growth is positively related to average summer temperatures.
Growth in the River Rhine nearly always exceeded that in the connected lakes, in spite
of lower chlorophyll-a concentrations. Water movement is probably essential to zebra
mussel growth.
In small and shallow Lake Veluwe eutrophication has led to the disappearance
of zebra mussels. Large phytoplankton concentrations enhanced the amount of
sedimented organic matter that covered the solid substrates. In the closed off Rhine-
Meuse estuary sediment transport limits the establishment of a permanent zebra
mussel population. In terms of biomass, zebra mussels are dominant invertebrate
species in the River Rhine and the connected lakes with a surface exceeding 50 km2.
Its role in the aquatic ecosystem is therefore important. In zebra mussel
colonies, an interesting ecological community may develop, consisting of very high
densities of worms, midge larvae and leeches. Diving ducks (e.g. Tufted duck,
Pochard and Scaup) are important regulators of zebra mussel densities. They
overwinter on the Dutch lakes that freeze only occasionally. Their population level has
increased steadily over the last 150 years. Several fish species (e.g. Eel and Roach)
also consume zebra mussels. Their impact on the zebra mussel population level is
1
-------
not known. The possibility of using zebra mussels in water management is now being
studied. Its filtering capacity can be used to decrease phytoplankton concentrations
by increasing the zebra mussel density. Experiments in two connected ponds at
Roggebotsluis revealed that 370 mussels/rrr were able to increase water clarity from
40 to 80 cm on average during summer. Hanging cultures of zebra mussels can
serve as a 'biological filter1 to remove contaminated suspended matter from the water
phase. Mucus sticks the rejected particles together as pseudofaeces that sediments
faster than the original suspended material. In this way, the pollution load can be
concentrated on a small surface. A biological filter is now being developed to prevent
the intrusion of polluted suspended matter in Lake Volkerak.
Zebra mussels are very suitable for several biomonitoring purposes. Since they
accumulate micropollutants, they can serve as bioindicators when concentrations in
the water phase are below the detection limit. Histopathological analyses of the body
tissues give good insight into the effects of environmental stress on the health of the
organism. Its suitability as an effect indicator of micropollutants in routine monitoring
is still being studied. Valve movements respond to very low concentrations of some
toxic chemicals and can be used as an early warning system for accidental pollution.
An operational pollution monitoring system is commercially explored in the
Netherlands.
If the spread of zebra mussels through the Great Lakes cannot be stopped, it
would be advisable to use them for water management purposes.
-------
ZEBRA MUSSEL BIOLOGY AND ECOLOGY IN NORTH AMERICA
Gerry Mackie, University of Guelph, College of Biological Science, Guelph, Ontario,
Canada.
Standing crops of zebra mussels in the Great Lakes are currently increasing by
an order of magnitude annually. Zebra mussels already outnumber native species of
unionid bivalves by three to four orders of magnitude. They are strongly byssate and
with their epifaunal mode of life are colonizing all hard substrates, a habitat that has
not been previously exploited by any benthic organism. The species is exhibiting life
history features which not only explain why zebra mussels are already the dominant
mollusc but indicate that some native species of bivalves may even be eliminated from
the Great Lakes. Compared to native species of bivalves, these features include:
external fertilization which allows for greater reproduction than internal fertilization; a
free-swimming larval stage for more effective and faster dispersal rates ( >250 km/yr
in Lake Erie); a longer (June to October) birth period; up to four orders of magnitude
greater recruitment and standing crops; and a faster growth rate. The population of
fj. polymorpha in Lake St. Clair has a different growth rate and life span than
European populations. The Lake St. Clair population is short-lived (2 years), fast-
growing (about 2 cm/yr) and small in adult shell length (less than 3 cm maximum
size). Massive encrustations of zebra mussels are hypothesized to have one or more
of the following effects on native unionid clams: (i) impairment of normal locomotion
and burrowing activities; (ii) prevention of valve closure by invasive growth of zebra
mussels thus exposing the unionid to predation, parasitism and environmental
extremes; (iii) prevention or limitation of valve gaping to affect normal metabolic
functions for feeding, growth, respiration, excretion and/or reproduction; (iv)
interference with normal functioning of the siphons and processes associated with
them (e.g. respiration and feeding); (v) stripping the water of food and nutrients
making little or none available to the unionid host which may ultimately starve to death;
(vi) causing shell deformities that may ultimately result in premature death of the
unionid; (vii) smothering by complete occlusion of the siphon region.
-------
SPECIES INVASIONS IN THE GREAT LAKES: HISTORICAL TRENDS AND
ENTRY VECTORS.
Edward L Mills, Department of Natural Resources, Cornell Biological Field Station,
Bridgeport, New York; Joseph H. Leach, Ontario Ministry of Natural Resources, Lake
Erie Fisheries Station, Wheatley, Ontario, Canada; Carol L Secor, Department of
Natural Resources, Cornell Biological Field Station, Bridgeport, New York; and James
T. Carlton, Maritime Studies Program, Williams College-Mystic, Mystic, Connecticut.
Scientists have been concerned for many decades about risks associated with
non-indigenous species in the Great Lakes ecosystem. The impact of exotic species
in the Great Lakes has been highly variable, ranging from those which have simply
supplemented existing communities to those which have posed a threat to the integrity
of the Great Lakes resource. The objective of this study has been to document
known non-indigenous flora and fauna in the Great Lakes since the early 1800s and to
ascertain the most probable vector each organism used to enter the lakes. For
purposes of this study, we defined a non-indigenous organism as a successfully
reproducing non-native species transported by human activity into the Great Lakes
watershed and an entry vector as the most probable means by which a species was
introduced by humans into the Great Lakes watershed. Our results clearly indicate
that exotic species have been successfully invading the Great Lakes since the early
1800s. To date, 115 different organisms have been identified as successfully
reproducing non-indigenous species in the Great Lakes. The bulk of these organisms
have been represented by aquatic plants (28%), fish (19%), algae (23%), oligochaetes
(10%), and mollusks (9%). While exotic species have been entering the Great Lakes
for at least two centuries, 46% have been identified in the Great Lakes during the last
30 years. This recent surge also coincides with the opening of the St. Lawrence
Seaway in 1959.
Non-indigenous Great Lakes species have entered the Great Lakes though a
variety of vectors. We have grouped entry vectors into five categories. These include
accidental release (e.g. bait, escape from fish culture, escape from cultivation, release
with infected fish, etc.), deliberate release (e.g. stocking or planting), waterfowl, ships
(e.g. solid ballast, ballast water, fouling), and migration through canals. Thirty-five
percent (40) of the exotic species identified for the Great Lakes have entered through
ship activities, and of these, 28% have entered through ballast water. The second
most common vector has been identified as accidental release (23%). Canals have
represented a small percentage (5%) of the entry vectors but species such as the
lamprey, alewife, and white perch, which have all entered the Great Lakes through this
vector, have had significant ecological and economic impact. Currently, vectors for
25% of Great Lakes exotic species are unknown.
Non-indigenous species have had both significant positive and negative impacts
in the Great Lakes ecosystem. We have identified 15 out of 115 non-indigenous
1
-------
species, or 10% of the successful invaders, which have had a significant ecological
and/or economic impact in the Great Lakes. This list includes the alewife, sea
lamprey, purple loosestrife, brown trout, Chinook salmon, furunculosis, white perch,
the spiny water flea, ruffe and zebra mussel.
-------
PREVENTING INTRODUCTIONS OF SPECIES INTO THE GREAT LAKES VIA
SHIPPING.
Lieutenant Commander Randy Helland, U.S. Coast Guard, Washington, D.C.
Introduction. The issue of exotic species introduced by discharges of ship
ballast water into the waters of the U.S. first came to national attention in 1988. Ballast
water has now been widely recognized as an important factor in the accidental
transport and discharge of exotic plants and animals. The question remains, how to
prevent further introductions of exotic plants and animals into U.S. waters.
Coast Guard Authorization. The Coast Guard Authorization Act (P.L. 101-225)
enacted in December 1989, required the Secretary of Transportation to submit to
Congress a report on the options to control the infestation of the waters of the United
States, including the Great Lakes, by exotic species from ships' ballast water. An
interim report was transmitted to Congress in August, 1990 which identified those
options. We indicated further research must be conducted on those options that
appear both practically and economically feasible. A final report will be submitted by
the end of 1991.
Options Study. The content of the interim report was not the result of my ideas
alone. It was the culmination of several brainstorming sessions at international
conferences such as this. Participants from Canadian provincial and state
governments, academia, industry, U.S. federal and state agencies, the Great Lakes
Fishery Commission, the International Joint Commission, and other organizations
provided significant input. However, in my opinion, the majority of credit must go to
Dr. Jim Carlton, author of the Paper on "Preventative Option for the Management and
Control of Accidental Intercontinental Transfers of Exotic Organisms by Ballast Water."
His paper provided the basis for the interim report.
During the many deliberations we did not look at the practicality, feasibility, or
associated costs of a particular control option because we felt that would limit the
brainstorming process. Additionally, our concentration was on commercial vessels
since they are suspected of being the major vector for transferring exotic species by
ballast water from overseas ports. Pleasure boats were not studied in depth; however,
we recognize that they are a major transportation vector for spreading exotic species
(e.g., zebra mussels) after they are introduced into the ecosystem. Pleasure boats will
be the topic of future studies.
There are several control options that require additional research into their
feasibility and practicality for shipboard use. They include ballast water exchange;
electrical current; heating ballast water; treatment facilities; use of screens and filters;
high velocity water flow; addition of biocidal agents; ultraviolet light; and ultrasound. I
will briefly discuss some of these options.
1
-------
Ballast Water Exchange. The most attractive option, at this point, is ballast
water exchange. Therefore, I will spend the most time addressing this control option.
Ballast water exchange appears to be the most attractive option because it requires
the least amount of change (i.e., modification to the vessel) and the process is
currently being done by vessels entering the Great Lakes in order to comply with the
Canadian voluntary guidelines. However, before we can make a final determination
regarding the feasibility of this option, there are two major concerns that must be
addressed; 1) ship safety and 2) biological effectiveness.
Some of the ship safety factors include:
* The safety and stability concerns for an unladen vessel to exchange ballast at
sea. Shifting of ballast during a voyage can be extremely hazardous due to the
potentially large free surface effects and rise in the vertical center of gravity. In
addition, the stress to the vessel's hull must be evaluated.
* The costs associated with delays, if any, when conducting at-sea ballast
exchange.
* Vessel manning needs and crew fatigue issues as a result of the extra work
load.
* The impact of coastwise voyages. Would this requirement force vessels to
proceed to open seas for ballast water exchange? Is it economically feasible?
The biological and ecological effectiveness of ballast water exchange also
needs to be determined. Rarely is there 100 percent exchange of water when vessels
exchange ballast water at sea. It is possible, for example, for several million gallons of
original water to remain at the bottom of ballast tanks and in various compartments
even after an "exchange" has been made. A study has been ongoing since June 1990
which is focusing on sampling "exchanged" water and determining the species and
numbers of residual organisms, if any, remaining in inbound vessels in transit on the
Great Lakes.
Heating Ballast Water. This also seems to be a feasible option. Questions
include 1) how hot does the water have to be in order to kill organisms, and 2) what
effects does heating ballast water have on the ships' hull?
Treatment Facilities. Treatment facilities would be used to off-load contaminated
water to the facility and, when necessary, to load treated water. Some liquid bulk
facilities may already have treatment facilities in place. While this option would provide
the needed protection against accidental discharges, it may be cost prohibitive for dry
cargo facilities to construct such a facility.
-------
Screens and Filters. The use of screens and filters has merit. Questions such
as 1) the strength of the mesh, and 2) the size of the mesh needed to filter the smaller
organisms must be resolved. A problem with this option is that filters and screens
small enough to capture and retain smaller organisms become clogged so quickly that
they would need to be constantly monitored and changed.
High Velocity Water Flow. It has been reported that very high velocity water
flow during pumping has been used in industrial water systems in an attempt to
increase the mortality of entrained organisms. Ships ballast pumps are high volume
but low pressure, and are not designed to achieve such velocities. Additional research
must be conducted to determine if such a pump can be modified for shipboard use.
Biocidal Agents. The use of biocidal agents in industrial applications has
reportedly been effective in controlling zebra mussels. I understand that several
industries in the State of New York have received approval to use chlorine in clearing
intake pipes of zebra mussels. For shipboard use, however, there are several
concerns or difficulties that must be addressed. First, the amount of poison required
to kill many species is unknown. Second, the total quantities necessary for various
species and the associated expense must be determined. Third, the method of
application, including access to the many separate ballast tanks while at the same time
achieving good mixing, needs to be considered. One application method might be to
access most tanks by sounding tubes or manhole covers; mixing could be achieved
by adding the biocide during ballasting. Fourth, potential human health hazards must
be considered. Fifth, subsequent disposal of the contaminated ballast water must be
dealt with. Sixth, highly trained personnel are required to apply the biocidal agent.
With any control option that is considered, it must be effective against
organisms in the upper, middle, and lower levels of the ballast tank.
Legislation. At this time there are over seven pieces of legislation currently
before congress that address this issue. However, I will discuss the two major pieces
of legislation, S. 2244 and H.R. 5390. Both the House and Senate versions, although
somewhat different, both mandate that the Coast Guard issue voluntary guidelines for
the Great Lakes within 12 months after enactment, and publish regulations for the
Great Lakes within 24 months after enactment. I anticipate that the final version will be
passed before the end of this Congress. The International Maritime Organization's
Marine Environment Protection Committee determined during last year's (1989)
meeting that exotic species are an international problem which requires an
international approach. As a result, a working group is planned for the meeting in
November of 1990 to begin work on developing international standards for preventing
the discharge of exotic species by ships' ballast.
Conclusion. According to U.S. Customs figures, there were over 67,000 port
calls in the U.S. in 1989 by commercial vessels. As you can see, we have a
-------
formidable task ahead. We will continue to work with the International Maritime
Organization, Canada, Mexico, and other organizations to develop the best possible
national program.
-------
SHIP BALLAST WATER DESIGNS TO KILL ORGANISMS BEFORE DISCHARGE.
John B. Woodward, University of Michigan, Department of Naval Architecture and
Marine Engineering, Ann Arbor, Ml.
Opening reference is made to papers presented at the workshop "Exotic
Species and the Shipping Industry," March 1-2, 1990. Possible options to eliminate
ship ballast water as a vector for migrating organisms, as discussed in those papers,
are listed here. They are:
Coat tank walls with biocide
Load pre-treated ballast from shore
Treat ballast with ultrasound
Treat ballast with electrical currents
Dilute sea water with fresh water
Discharge ballast to shore facility
Pump water at high velocity
Remove organisms by screening/filtering
Treat ballast with ultraviolet radiation
Dilute fresh water with sea water
Exchange ballast offshore
Brief comments are made on each of these, with the general tenor of comments being
that the effectiveness and even feasibilities of these options are virtually unknown.
The ballasting requirements (i.e. tonnages of ballast, and times allowed for
ballasting and deballasting) of several disparate ship types are presented. It is seen
that for some ships, especially bulk carriers, the tonnages are large and the times are
short, circumstances that may make treatments during ballasting/deballasting difficult if
not completely infeasible.
Speculative quantitative analysis is done for two possible on-board ballast
treatment methods. One is heating ballast to a lethal temperature through use of
exhaust heat from a ship's propulsion engine. Back-of-envelope calculations show
that if the temperature is low enough (120° F) and the time available long enough (six
days), such a thing might be accomplished. It is noted, however, that the concept
might require heavy insulation of ballast tanks, and might usurp a heat source that is
often fully exploited for other purposes.
The other speculative analysis concerns use of sand filters, similar to those
commonly used in municipal water treatment, for on-board cleansing of ballast water.
The figures show that such a concept may be feasible, but major uncertainties are
obvious (e.g. would ship motion disturb the filter, would sufficient space be available
aboard ship for the filters?).
1
-------
In closing, a reminder is given that the Great Lakes are often spoken of,
especially in Michigan, as a world-unique resource to the people who live in their
watershed. If such beliefs are as strong as their proponents allege, then the
"unthinkable solution", namely closing the Lakes to marine intercourse with the outside
world, should be considered.
-------
STRATEGY FOR CONTROLLING THE DREISSENA POPULATION IN NORTH
AMERICA.
V.N. Karnaukhov, Institute of Biological Physics of the Academy of Sciences of the
USSR, Pushchino, Moscow District, 14229r USSR.
A.V. Karnaukhov, NTTM "Contract" Center, Smolenskii Bui var, 4, Moscow, 119034,
USSR.
Essence of the Problem. In the summer of 1988, a new type of mollusk not
native to the Great Lakes was discovered in Lake St. Clair in the Great Lakes system.
The American press began to call this newcomer the "zebra mussel". In the course of
a single year (1988/89) in several regions of Lake St. Clair the population of this
mussel grew a thousand fold, from 0.5 mussels/nf to 4,500 mussels/m2.
This explosive growth of the new type of mollusk is a phenomenon typical of
the introduction of a species into a new habitat and may have a major negative
economic effect. It turned out that larvae of the zebra mussel (from here on we will
call it by its scientific name, Dreissena) were brought to the Great Lakes by ships
discharging ballast water taken aboard in Europe at the mouths of the Elbe and Rhine
rivers.
Even now, in just one year, the drastic increase in this mussel population is
creating complex economic problems for hydroengineering and water intake
installations. For example in Monroe, Michigan repair of damaged water supply lines
was estimated to cost fifty million dollars; in Cleveland, Ohio one-hundred million
dollars. The repair of a water intake cooling system at a thermal power station in
Detroit, Michigan is estimated at one-hundred and fifty million dollars, and one to two
years after these repairs, similar amounts will be needed for new repairs, etc.
We must consider that the mussel intrusion has just begun and that it will
embrace all the fresh waters of the United States and Canada, despite the control
measures taken. Control has come too late; there is a high probability that this
mussel has penetrated the Mississippi basin.
It is quite natural that administrators and scientists in the United States and
Canada, faced with this complex ecological problem that has caused such economic
losses, would raise the problem of developing a strategy for bringing the problem
under control. It is clear, however, that the right strategy can be developed only if we
correctly understand the essence of the situation that has arisen in the Great Lakes,
or, more accurately, on the North American continent, that is, if we arrive at the proper
diagnosis. Are we on the threshold of an ecological crisis for which there are parallels
in. Europe, or are we on the threshold of a unique ecological disaster? The answer to
this important question will also determine the strategy for action.
-------
The Ecological Crisis. The mussel Dreissena polymorpha evolved as a species
millions of years ago in the huge saline waterbasin which includes the present Aral,
Caspian, Azov, and Black seas. It was in the mouths of the rivers that flowed into
these seas, such as the Volga, Don, Dnieper, and Danube, that there were stable
ecological communities in which the Dreissena population was in equilibrium with its
natural enemies.
About 200 years ago, evidently in connection with the construction of canals
and increased eutrophication of the water basins, Dreissena began to penetrate the
North European rivers that emptied into the Baltic Sea. Every time Dreissena entered
a new region approximately the same situation developed as now in the Great Lakes -
damage to water intake equipment, water supply lines, and other hydroengineering
installations.
About 40-50 years ago the Dreissena mussel problem arose again in the USSR
because that mollusk began to move quickly northward along rivers (Volga, Don,
Dnieper), the mouths of which were the "motherland" of this mussel. The reason for
the abrupt growth of the Dreissena population in this case was the sharp increase in
the contamination of these rivers by biogenic and organic elements in connection with
the flooding of large regions caused by the construction of a series of hydroelectric
station reservoirs.
In this case, we can see a clear example of the main reason for population
explosion of Dreissena. namely water pollution; the increase of the biomass of
microplankton, the food of the filtrator mollusk Dreissena. in these polluted waters. I
prefer to call this phenomenon an ecological crisis (by analogy with the human
recovery after a serious illness), since as a result of this process a more powerful
system of biological self-purification of the water basin takes place, in which the
mollusk-filtrators (including Dreissena) play a decisive role.
The crisis process itself - the establishment in the reservoir of a new, greater
degree of contamination of the system of self-purification - takes about 20-30 years,
depending on the features of the specific water basin. This corresponds in its general
features to what takes place in a number of reservoirs in the European part of the
USSR. When the biomass of Dreissena increases, the biomass of the river roach
(Rutilus rutilus). one of the most widespread types of fish in the rivers of the European
USSR, also increases. In such water basins the roach, reaching a length of 13-15 cm,
feeds on Dreissena. Its growth rate increases and it becomes larger and fatter.
When we first heard of the intrusion of Dreissena into the Great Lakes, we
presumed that North America was on the threshold of a major ecological crisis in its
freshwater basins, which would gradually spread from one water basin to another and,
therefore, the general continuing crisis would be somewhat greater than was generally
the case for Europe. The process may last from 30 to 50 years.
-------
Strategy for a Crisis Situation. The cost of repair of hydroengineering
installations, including repair of water supply and water intake systems for that period
(30-50 years) over a vast territory may amount to 200 to 500 billion dollars. The
natural inclination to reduce these expenses should result in the introduction into North
America of a number of European methods of protecting hydroengineering
installations from Dreissena and the introduction of new methods based on more
extensive research into the biology and ecology of this mussel.
However, the application of these protective methods should be strictly local
and controlled. They should be limited, for example, to physical and biological
(ecological) methods. The uncontrolled use of chemical compounds (biocides,
molluscicides) supposedly specific only to mollusks, should be avoided.
Our research has established that the high resistance of the mussels to
contamination of the medium and the effects of toxic chemical is connected with the
presence in their cells of high concentrations of carotinoids that participate in the
formation of energy producing intracellular organoids which we have called
cartionoxisomes. A similar type of organoid ensures the resistance of the cells
(particularly of the brain and heart) of middle-aged and old humans. Therefore, toxic
chemicals specific for mollusks may also be specific for middle-aged and elderly
humans.
Instead of using chemical methods to reduce the population density of the
mussels, one should use ecological methods of control. One of these methods
consists of industrial removal of some of the mussels from the water basins and
converting them into protein fodder. In the process a technology may be developed
for using the water basin substrates for cultivation of the mussels. When appropriate
laws have been made, and probably tax breaks, this method may yield annually
millions of tons of valuable protein fodder rich in vitamins and microelements and thus
reduce the general losses involved in the introduction of Dreissena into water basins.
The biomass of Dreissena may also be used as raw material for the pharmaceutical
industry.
The proposed method of reducing the population density of Dreissena will
reduce their total burden on water intake and hydroengineering installations. Besides,
such systems of basin substrates for cultivating mussels may be located in the
immediate vicinity of hydroengineering installations for local protection from their
encrustation with Dreissena.
This, in its general outlines, should be the strategy for control of the Dreissena
population in North America, if what is now happening is the initial stage of the
ecological crisis of the water basins.
-------
The Possibility of an Ecological Disaster. Unfortunately, the information we
have does not exclude the possibility that the events taking place in the Great Lakes
are the beginning of an ecological disaster, the likes of which have not been
experienced in Europe or the USSR. I have in mind the results of laboratory research,
conducted by Paul Hebert at Windsor University, reproducing the growth rate of the
Dreissena population of Lake St. Clair. This growth rate greatly exceeded that usually
observed in Europe in the first years of the intrusion of this mussel into a water basin
new to it.
These results put us on guard and we attempted to use a mathematical model
for analysis of the reasons for such a high rate of population growth of these mussels.
The results appeared paradoxical at first glance. The anomalously high growth rate of
the mussel population in Lake St. Clair could occur only if there were no (or almost
no) fish in the Great Lakes able to eat the mussels.
Analysis of the literature showed that this conclusion seems paradoxical only at
first glance. In Europe, carp are the principal predators of Dreissena. including the
aforementioned roach (Rutilus rutilus). In all, there are about 1,500 species of carp,
including about 50 species that inhabit the Great Lakes. However, carp can be
divided into two groups:
1) those with weak pharyngeal teeth that are not capable of feeding on
mussels;
2) those with two or three rows of strong pharyngeal teeth easily capable of
crushing mussel shells.
In Europe and especially in the mouths of the rivers of the Azov-Caspian basin,
there are a considerable number of fish belonging to group 2, for which mollusks, and
especially Dreissena. are the main source (70-80%) of their food. These are principally
subspecies of the roach such as the Caspian roach (Rutilus caspicus) and the Azov-
Black Sea carp (Rutilus heckeli). which, perhaps, came into being at the same time as
Dreissena. These species of fish form a considerable part of the commercial catch of
fish in the lower course of the Volga, Don, and Dnieper.
Among other molluscivorous fish in this basin are the roaches Rutilus frisii.
Rutiius frisii cutum. the gustera (Blicta bioerkna). the Aral barbel (Barbus
brachycephalus). and sturgeons (Acipensetidae).
In contrast to this, in the rivers of North America most of the carps belong to
group 1, these with weak pharyngeal teeth evidently incapable of feeding on mussels.
There appear to be few fish capable of feeding on mussels. This is the reason (the
lack of molluscivorous fish in the North American water basins) that may lead to an
ecological crisis of disastrous proportions in these waters. The scenarios for the
-------
development of this ecological crisis may differ depending on the characteristics of
specific water basins.
In the most favorable scenario of an ecological disaster, the biomass
(population) of the Dreissena mussel will grow much faster and reach the maximum
sooner with a total population of mussels several times that of European water basins.
In contract to crises in European water basins, the biomass of fish in the case of a
disaster will decrease because the fiitrator mollusk Dreissena with its gigantic biomass
will be a strong competitor with the fry and larvae of fish for microplankton, and with
small Crustacea that serve as food for fish fingerlings.
In the first stages, this should lead to a reduction of the fry and fingerlings of
native fish. As of August, 1990 we do not have direct data to confirm this hypothesis.
However, the laboratory data of Paul Hebert of August, 1989 showed a reduction of
the fat content of native species of double-walled, fiitrator mollusks (Unionides) as a
result of the competition for food (microplankton) by Dreissena.
The filtering action of Dreissena reduces the population (biomass) of
microplankton and has reduced the turbidity of the Detroit River. The increased
transparency of the water of the Great Lakes has been noted in other work as well.
Perhaps by the fall of 1990 there will be direct data on the change in population of the
larvae and fingerlings of native species of fish.
Thus, the maximum Dreissena population in the Great Lakes will be determined
solely by the supplies of biogenic elements and organic substances capable of
transforming into microplankton. When the Dreissena population reaches its
maximum, it will begin to fall to a level determined by the entry rate of biogenic
elements and organic substances into the water basins and the rate of their
transformation into microplankton.
In a less favorable scenario for disaster, after the maximum population of
Dreissena has been reached the system will convert into an unstable regime whereby
most of the mussels will perish because of a still unknown disease that is highly
probable with such a large Dreissena population density. This means that in the
waters of the Great Lakes there may be millions of tons of decaying biomass which
will lead to a sharp drop in the oxygen content of the water and complete destruction
of the fish. The quality of the drinking water will become very low.
In the best case, the diatomic microplankton in the waters of the lakes will
increase rapidly, a normal level of oxygen will be reached, and the explosion of the
Dreissena population will occur again. In the worst case, the oxygen-deprived waters
of the Great Lakes will capture blue-green autotrophic-heterotrophic microorganisms
capable of precipitating toxins into the surrounding medium. Then the water will
become unsuitable for drinking.
-------
Disaster Strategy. The possibility of a disaster is associated with the absence
of molluscivorous fish in North America. Under these circumstances the creation of an
industry to extract and process the Dreissena mussel into protein fodder is the only
possibility for controlling the Dreissena population in North America that would not
have adverse ecological side-effects. However, this measure may not be sufficient or
realizable in time and it may be necessary to introduce molluscivorous fish into North
America in large numbers.
What Should Be Done in the Immediate Future? Inasmuch as events develop
rapidly, it may be necessary to create an Emergency Dreissena Ecological Program in
no more than 2-3 years. The aim of this program would be to concentrate efforts to
learn as quickly as possible what it is that threatens North America - an ecological
crisis or an ecological disaster - and to prepare for the worst case scenario.
It is probable that the following would be the basic directions taken by this
program:
1) Sharply increase research on the changes in the ecological communities
of the Great Lakes, and first of all in Lake St. Clair, to find the answer to
the question posed here; are the developing events the beginning of a
crisis or a disaster?
2) In parallel, arrange for American and Canadian scientists to conduct
research on the ecological communities of Dreissena in its "native land,"
the Aral-Caspian-Azov-Black Sea basin, where this mussel has natural
enemies and competitors. This is necessary to help determine whether
molluscivorous fish should be introduced into North American waters if
the situation reaches disaster proportions.
3) To urgently undertake experiments on creating a mussel extraction
industry for conversion into protein fodder. At the same time the legal
aspects of such an industry must be explored, including, probably, tax
breaks.
4) Create the conditions and mechanisms for joint action of European
countries and the USSR in developing and applying methods of
protecting hydroengineering installations from encrustation by Dreissena
and testing these methods in the Great Lakes.
5) Sharply expand research on the biology and ecology of Dreissena to
develop new methods for their control and for preventing their
encrustation of hydroengineering installations, employing the scientific
potential of various countries and creating, if possible, regional
information centers and an infrastructure of scientific research.
-------
THE ZEBRA MUSSEL: CHEMICAL AND PHYSICAL CONTROL METHODS FOR
INDUSTRY
Donald P. Lewis, Aquatic Sciences Inc., St. Catharines, Ontario, Canada
The introduction of the zebra mussel (Dreissena polymorpha) to the Great Lakes
in 1985/1986 has had a dramatic impact on water users located on these lakes,
connecting waterways, and associated tributaries.
Aquatic Sciences has been helping industry cope with the zebra mussel
phenomenon since 1988, initially in a monitoring role and then as a consultant designing
and implementing zebra mussel control programs for industry and undertaking research
on alternate control methods.
This paper provided a review of the mussel's biology as it relates to mussel control
and then provided a survey of chemicals that have been used or proposed for control of
the zebra mussel in municipal and industrial settings.
The majority of chemical control programs recommended in European literature
focused on the use of chlorine which led to initial attempts in North America using
chlorine at levels between 0.5 ppm and 2 ppm for durations of 7 to 21 days. The
potential usefulness of other oxidants (bromine, potassium permanganate, hydrogen
peroxide, ozone) as well as molluscides and toxic coatings was discussed. The
importance of pH and temperature of incoming water was emphasized for all chemical
control programs.
The use of physical controls such as heat, hydrosonics, and electricity was
reviewed as potentially useful methods of reducing chemical use. Research efforts in
these areas were reviewed.
-------
SUCCESSFUL MANAGEMENT OF AN INTRODUCED SPECIES. SEA LAMPREY:
PAST, PRESENT AND FUTURE CONTROL STRATEGIES.
Terry J. Morse, U.S. Fish and Wildlife Service, Marquette Biological Station, Marquette,
Michigan.
The Sea Lamprey, Petromvzon marinus. is a species that parasitizes other fish
and is endemic to the North Atlantic. Lampreys migrated through the St. Lawrence
Seaway into Lake Ontario and became common there in the 1800's. Niagara Falls, a
natural barrier to the migration of lampreys into the other Great Lakes, was bypassed
by the Welland Canal in 1829 which provided lampreys a direct invasion route to the
other Lakes. By the late 1930's sea lampreys had spread throughout the Lakes and
targeted lake trout (Salveiinus namaycush). the dominant fish in the food chain, as a
primary food source. In the absence of natural controls, the sea lamprey population
expanded and quickly devastated the lake trout populations in Lakes Michigan and
Huron and in much of Lake Superior.
As a result of the total collapse of the fisheries in the Great Lakes, the Great
Lakes Fishery Commission was created by convention between the United States and
Canada to improve fishery resources and manage the sea lamprey. Early control
efforts centered on blocking spawning migrations with physical and electrical barriers.
These efforts were ineffective as the barriers were easily negotiated during periods of
high water, which were typical during spring spawning migrations. The search for a
better control technique led to testing of over 6,000 chemicals by scientists at the
Hammond Bay Research Laboratory. Finally, a larvicide, TFM (3-triflouromethyl-4-
nitrophenol), was found to selectively kill sea lampreys while having minimal effects on
most non-target organisms, and proved to be non-toxic to humans and other
mammals. Since the advent of chemical control in the Great Lakes in 1960, sea
lamprey populations were reduced by 95%. Today, the fisheries in the Lakes have
rebounded to a value in excess of $4 billion annually, due largely to the success of the
Sea Lamprey Management Program, which returns over $400 for every dollar spent for
control.
Although lampricides are currently the primary control tool, we are currently
striving to implement an integrated management approach for controlling sea
lampreys. This approach includes the following non-biocidal control methods which
would be used concurrently to control lampreys: physical and electrical barriers with
lamprey traps, and the Sterile-Male Release Technique.
Low-head barrier dams have been constructed on 28 streams in U.S. and
Canada to restrict spawning migrations of sea lampreys. Lamprey traps are fished in
conjunction with barriers to capture spawning-phase lampreys during spring migration.
Although trapping efficiency varies with the site, efficiencies as high as 75% have been
documented. Over 80,000 spawning-phase lampreys were captured during the 1989
1
-------
spawning season. Experimental electrical barriers using new electronics technology
have shown potential for the integrated control approach. The Michigan Department
of Natural Resources tested the new electric barriers on the Pere Marquette and
Jordan rivers, and a similar version was successfully tested on the Ocqeouc river by
U.S. Fish and Wildlife Service personnel.
The Sterile-Male Release Technique, the most promising of the new control
techniques, has been used successfully to control or eradicate insect pests.
Successful execution of this technique is dependent on capturing spawning-phase
lampreys, sterilizing the males and placing them back into the streams to mate with
the females, which would result in unfertilized eggs. Preliminary studies have shown
that spawning-phase lampreys could be effectively sterilized by an injection of Bisazir,
a chemical sterilant, without adversely affecting the spawning behavior. Temporary
intensification of chemical control combined with Sterile-Male Release and optimal use
of barriers with traps, might reduce the sea lamprey population to a point when the
release of sterile males would be all the control necessary. The Sterile-Male Release
Technique is scheduled to be implemented in Lake Superior and the St. 'Mary's River
in 1991.
The lamprey control program has successfully contributed to the recovery of
the fisheries in the Great Lakes by using biocides to control lampreys. However, we
are fervently working towards less dependency on biocides and more of an integrated
control approach, utilizing non-biocidal techniques whenever possible.
-------
APPENDIX B
LIST OF PARTICIPANTS
INTRODUCED SPECIES WORKSHOP
U.S. EPA
SEPTEMBER 26-28, 1990
-------
Participants - Introduced Species Workshop, US EPA, Sept. 26-28,1990
Pilie Bunnell
ESSA, Ltd.
3rd Floor, 1765 W. 8th Ave.
Vancouver, BC
CANADA V6J 5C6
Ph: 604-733-2996
Fax: 604-733-4657
Murray Charleton
Lakes Research Branch
National Water Research Institute
P.O. Box 5050
Burlington, ON
CANADA L7R 4A6
Ph: 416-336-4758
Fax: 416-336-4989
Rudy D'Allesandro
Org. for American Soviet Exchanges
1430 K Street NW Suite 1200
Washington, DC 20005
USA
Ph: 202-393-0985
Fax: 202-393-0989
Ronald Derrnott
Dept. of Fisheries & Oceans
Great Lakes Fisheries Lab, CCIW
P.O. Box 5050
Burlington, ON
CANADA L7R 4A6
Ph: 416-336-4568
Fax: 416-336-4819
Bill Freeman
Office of International Activities
US EPA
401 M St. SW
Washinton, DC 20460
USA
Ph: 202-245-3508
Fax: FTS-382-4470
Vic Cairns
Canadian Center for Inland Waters
Dept. of Fisheries & Oceans
867 Lakeshore Rd., P.O. Box 5050
Burlington, ON
CANADA L7R 4A6
Ph: 416-336-4568
Fax:
Renata Claudi
Ontario Hydro
700 University Ave. A7A4
Toronto, ON
CANADA M5G 1X6
Ph: 416-592-9140
Fax: 416-592-7066
Jeff Denny
Env. Res. Lab - Duluth
US EPA
6201 Congdon Boulevard
Duluth, MN 55804
USA
Ph: 218-720-5518 FTS-780-5518
Fax: 218-720-5539
Margaret Dochoda
Great Lakes Fishery Commission
1451 Green Road
Ann Arbor, Ml 48105
USA
Ph: 313-662-3209
Fax: 313-668-2531
Tom Freitag
US Army Corp of Engineers
Environmental Analysis Branch
P.O. Box 1027
Detroit, Ml 43231-1027
USA
Ph: 313-226-6753
Fax: 313-226-2056
-------
Bob Haas
Institute for Fish Research
Michigan Dept. of Nat. Resources
33135 South River Road
Mt. Clemens, Ml 48045
USA
Ph: 313-465-4771
Fax:
Randy Helland
US Coast Guard (G-MTS)
2100 2nd St. SW
Washington, DC 20593
USA
Ph: 202-267-0495 FTS-267-0475
Fax: 202-267-4085
Bill Hoppes
Water Management Division
U.S. EPA/Region 2
26 Federal Plaza
New York, NY 10278
USA
Ph: 212-264-5352 FTS-264-5352
Fax: 212-264-2194
Jory Jonas
Wis. Sea Grant Advisory Office
ES105, UW-Green Bay
Green Bay, Wl 54311-7001
USA
Ph: 414-465-2798
Fax: 414-465-2376
William Hall
U.S. Coast Guard
1240 E. 9th St.
Cleveland, OH 44199
USA
Ph: 216-522-3959 FTS-942-3959
Fax: 216-522-7537
Larry Herman
Env. Res. Lab - Duluth
US EPA
6201 Congdon Boulevard
Duluth, MN 55804
USA
Ph: 218-720-5568
Fax: 218-720-5539
Joe Hudek
US EPA/Region 2
2890 Woodbridge Avenue
Edison, NJ 08887-3679
USA
Ph: 212-340-6713 FTS-340-6713
Fax: 212-340-6622 FTS-340-6622
V.N. Karnaukhov
Institute of Biophysics
Academy of Sciences USSR
Pushino Moscow Reg., 142292
USSR
Ph:
Fax:
Mike King
University of MN-Duluth
Department of Biology
10 University Dr.
Duluth, MN 55812
USA
Ph: 218-726-6127
Fax:
Russ Kreis
Large Lakes and Rivers Res. Branch
US EPA, Env. Res. Lab. - Duluth
9311 Groh Road
Grosse He, Ml 48138
USA
Ph: 313-692-7615 FTS-378-7615
Fax: 313-692-7603
-------
Robert Lange
New York Dept. Env. Conservation
50 Wolf Rd.
Albany, NY 12233
USA
Ph: 518-457-6937
Fax:
Carl Latta
Institute for Fish Research
Michigan Dept. of Natural Resources
Ann Arbor, Ml 48109
USA
Ph: 313-663-3554
Fax:
Joseph Leach
Ministry of Natural Resources
Lake Erie Fisheries Station
RR#2
Wheatley, ON
CANADA NOP 2PO
Ph: 519-825-4684
Fax:
Gerry Mackie
University of Guelph
Department of Zoology
Guelph, ON
CANADA N1G 2W1
Ph: 519-824-4120 ext.3505
Fax:
John Lehman
University of Michigan, Ann Arbor
Department of Biology
Ann Arbor, Ml 48109
USA
Ph: 313-763-4680
Fax:
Peter Maitland
Fish Conservation Center
Easter-Cringate
Stirling FK7 9QX,
SCOTLAND, UK
Ph: 10288-011-44-0786-51312
Fax: 44-031-445-3943
Leif Marking
National Fisheries Research Center
U.S. Fish and Wildlife Service
P.O. Box 818
Lacrosse, Wl 54602
USA
Ph: 608-783-6451
Fax: 608-783-6066
Howard McCormick
Env. Res. Lab - Duluth
US EPA
6201 Congdon Boulevard
Duluth, MN 55804
USA
Ph: 218-720-5514 FTS-780-5514
Fax: 218-720-5539
Ron Martin
Bureau of Water Resources Mgt.
Wisconsin Dept. of Natural Resource
101 S. Webster St.
Madison, Wl 53707
USA
Ph: 608-266-9270
Fax: 608-267-2800
David McNeill
New York Sea Grant Extension Pgm.
248 Hartwell Hall, State University
Brockport, NY 14420
USA
Ph: 716-395-2638
Fax:
-------
Edward Mills
Cornell University
Biological Field Station
900 Shackleton Point Rd.
Bridgeport, NY 13030
USA
Ph: 315-633-9243
Fax:315-633-2358
Gary Montz
Minnesota Dept. of Nat. Resources
Ecological Services
500 Lafayette Rd.
St. Paul, MN 55155
USA
Ph: 612-297-4888
Fax: 612-296-3500
Peter Moyle
University of California, Davis
Department of Wildlife & Fisheries
Davis, CA 95616
USA
Ph: 916-752-6355
Fax:
Russell Moll
Michigan Sea Grant College Program
2200 Bonisteel Boulevard
Ann Arbor, Ml 48109
USA
Ph: 313-764-2426
Fax:
Terry Morse
Marquette Biological Station
U.S. Fish & Wildlife Service
446 E. Crescent St.
Marquette, Ml 49855
USA
Ph: 906-226-6571
Fax:
Carol Murray
ESSA, Ltd.
#308-9555 Yonge St.
Richmond Hill, ON
CANADA L4C 9M5
Ph: 416-508-0860
Fax: 416-508-0863
Tom Naiepa
Great Lakes Env. Res. Lab, NOAA
2205 Commonwealth Boulevard
Ann Arbor, Ml 48105
USA
Ph: 313-668-2285
Gary Peters
Saginaw/Midland Water Supply Corp.
4678 S. Three Mile Road
Bay City, Ml 48706
USA
Ph: 517-684-2220
-------
Anton Reznicek
University of Michigan Herbarium
N. University Bldg.
Ann Arbor, Ml 48109
USA
Ph: 313-764-5544
Fax:
Mike Rose
ESSA, Ltd.
#308-9555 Yonge St.
Richmond Hill, ON
CANADA L4C 9M5
Ph: 416-508-0860
Fax: 416-508-0863
Bill Rosenberg
US EPA
401 M St. SW
Washington, DC 20460
USA
Ph: 202-382-7400 FTS-382-7400
Fax:
Craig Sandgren
Center for Great Lakes Studies
600 E. Greenfield Ave.
Milwaukee, Wl 53204
USA
Ph: 414-229-4279
Fax:
Peter Seidl
International Joint Commission
P.O. Box 32869
Detriot, Ml 48232
USA
Ph: 313-226-2170
Fax: 519-256-7791
Henk Smit
Inst. for Inland Water Management
Van Leeuwenhoekweg 20
3316AV Dordrecht,
Hi*
Nataliya Smirnova
Inst. Biology of Inland Waters
Nekouzskiy Raion
Yaroslavskaya Oblast
Borok
USSR
Ph:
Fax:
Fred Snyder
Ohio Sea Grant Ex
Camp Perry, Buil<
Port
-------
Edward Mills
Cornell University
Biological Field Station
900 Shackleton Point Rd.
Bridgeport, NY 13030
USA
Ph: 315-633-9243
Fax: 315-633-2358
Gary Montz
Minnesota Dept. of Nat. Resources
Ecological Services
500 Lafayette Rd.
St. Paul, MN 55155
USA
Ph: 612-297-4888
Fax: 612-296-3500
Peter Moyle
University of California, Davis
Department of Wildlife & Fisheries
Davis, CA95616
USA
Ph: 916-752-6355
Fax:
Russell Moll
Michigan Sea Grant College Program
2200 Bonisteel Boulevard
Ann Arbor, Ml 48109
USA
Ph: 313-764-2426
Fax:
Terry Morse
Marquette Biological Station
U.S. Fish & Wildlife Service
446 E. Crescent St.
Marquette, Ml 49855
USA
Ph: 906-226-6571
Fax:
Carol Murray
ESSA, Ltd.
#308-9555 Yonge St.
Richmond Hill, ON
CANADA L4C 9M5
Ph: 416-508-0860
Fax: 416-508-0863
Tom Nalepa
Great Lakes Env. Res. Lab, NOAA
2205 Commonwealth Boulevard
Ann Arbor, Ml 48105
USA
Ph: 313-668-2285
Fax:
Gar/ Peters
Sag'naw/Midland Water Supply Corp.
4678 S. Three Mile Road
Bay City, Ml 48706
USA
Ph: 517-684-2220
Fax:
Tom Poleck
Safe Drinking Water Branch
US EPA/Region 5 [5WD-TUB-9]
230 South Dearborn Street
Chicago, IL 60604
USA
Ph: 313-353-2151 FTS-353-2151
Fax:
Mike Quigley
Great Lakes Env. Res. Lab, NOAA
220I5 Commonwealth Boulevard
Ann Arbor, Ml 48105
USA
Ph: 313-668-2285
Fax:
-------
Anton Reznicek
University of Michigan Herbarium
N. University Bldg.
Ann Arbor, Ml 48109
USA
Ph: 313-764-5544
Fax:
Mike Rose
ESSA, Ltd.
#308-9555 Yonge St.
Richmond Hill, ON
CANADA L4C 9M5
Ph: 416-508-0860
Fax: 416-508-0863
Bill Rosenberg
US EPA
401 M St. SW
Washington, DC 20460
USA
Ph: 202-382-7400 FTS-382-7400
Fax:
Craig Sandgren
Center for Great Lakes Studies
600 E. Greenfield Ave.
Milwaukee, Wl 53204
USA
Ph: 414-229-4279
Fax:
Peter Seidl
International Joint Commission
P.O. Box 32869
Detriot, Ml 48232
USA
Ph: 313-226-2170
Fax: 519-256-7791
Henk Smit
Inst. for Inland Water Management
Van Leeuwenhoekweg 20
3316AV Dordrecht,
The NETHERLANDS
Ph: 10288-011-31-78-322616
Fax: 10288-011-31-78-315003
Nataliya Smirnova
Inst. Biology of Inland Waters
Nekouzskiy Raion
Yaroslavskaya Oblast
Borok
USSR
Ph:
Fax:
Fred Snyder
Ohio Sea Grant Extension Program
Camp Perry, Building 3, Room #12
Port Clinton, OH 43452
USA
Ph: 419-635-4117
Fax: 419-734-6898
Gilman Veith
Env. Res. Lab - Duluth
US EPA
6201 Congdon Boulevard
Duluth, MN 55804
USA
Ph: 218-720-5550 FTS-780-5550
Fax: 218-720-5539
G.A. Vinogradov
inst. Biology of Inland Waters
Nekouzskiy Raion
Yaroslavskaya Oblast
Borok
USSR
Ph:
Fax:
-------
Glen Warren
Great Lakes Nat. Pgm. Office
EPA (5-GL)
230 South Dearborn St.
Chicago, IL 60604
USA
Ph: 312-886-2405 FTS-886-2405
Fax:
Paul Wendler
Michigan Wildlife Foundation
4800 Bretton
Saginaw, Ml 48602
USA
Ph: 517-792-3432
Fax:
Chris Wedeles
ESS A, Ltd.
#308-9555 Yonge St.
Richmond Hill, ON
CANADA L4C 9M5
Ph: 416-508-0860
Fax: 416-508-0863
Phyl is Windle
Office of Technology Assessment
U.S. Congress
Wasiington, DC 20510
USA
Ph: 202-228-6533
Fax:
John B. Woodward
University of Michigan - Ann Arbor
Dept. of Naval and Marine Eng.
2600 Draper
Ann Arbor, Ml 48109-2145
USA
Ph: 313-764-8269
Fax:
David Yount
Env. Res. Lab - Duluth
US EPA
6201 Congdon Boulevard
Duluth, MN 55804
USA
Ph: 218-720-5752 FTS-780-5752
Fax: 218-720-5539
aU.S GOVERNMENT PRINTING OFFICE 1991 - 5 t B -1 8 7/2 0 5 8 3
------- |