Download File - Jarrett Friesen

92%
An Overview of the Zebra Mussel Invasion of the Great Lakes
Jarrett Friesen
7705025
BIOL 3600 – A01
Dr. Jillian Detwiler
February 11, 2014
Introduction
Marine invasive species are a growing global concern. Although many invasive species
are introduced into non-native waters, only a small percent of these species are able to establish
and flourish (Molnar et al, 2008). Once an invasive species becomes established, it is unrealistic
to expect its complete removal. The focus must be on the prevention of initial introduction into a
foreign waterway. This involves identifying the most common pathway introducing invasive
species and the potential threat a species will have once introduced (Molnar et al, 2008).
Globally, shipping is the most prevalent pathway to invasive species introduction, slightly over
half of which are harmful to the area they are introduced to (Molnar et al, 2008). Zebra mussels
(Dreissena Polymorpha) are a prime example of an invasive marine species affecting Canada
and the United States of America since their introduction into the Great Lakes. The introduction
of zebra mussels through the deposition of ballast water from ships has caused many problems to
the natural ecosystems and anthropogenic activities in this lake system. These problems stem
from the ability of zebra mussels to rapidly spread in population and spatial extent, interrupting
the natural processes that occur in the Great Lakes. With very few solutions, the main objective
in combating the zebra mussel pests is to control their geographic spread, population size, and
negative impact on the human and natural activities in the Great Lakes.
Zebra Mussels
Zebra Mussels are small, freshwater benthic filter-feeders that can consume up to a litre
and a half of water a day (Zorpette, 1996). They filter a variety of substances from the water
including algae, plankton, and pollution contaminating the water. Zebra mussels inhabiting the
Great Lakes were able to quickly dominate these lakes through their rapid reproductive
1
capabilities and aggressive nature. Female zebra mussels can produce a staggering one million
eggs per year and are able to begin reproduction one year after birth (Zebra Mussels, 2010).
Zebra mussels anchor to solid surfaces when filtering water by using byssal threads. Zebra
mussels prefer solid material to attach to but have been found occupying sand and even mud
(Berkman et al, 1998). They also have the capability of attaching to other marine species
including native mussels and another introduced mussel species, the quagga mussel. This factor,
as well as the diverse environment of the aquatic habitat in the Great Lakes, allows the zebra
mussel to inhabit many areas throughout the Great Lakes (Naddafi, 2010).
Invasion
Zebra mussels were first introduced to the Great Lakes through Lake St.Clair in 1986.
Zebra mussels are most prevalent in Lake Erie but can be found in all of the Great Lakes
(Zorpette, 1996). Zebra Mussels were first discovered in Lake Erie on natural gas well markers
and well heads in the Great Lakes (Carlton, 2008). They were transported through human
commercial shipping through ballast water which when added to the ship serves to balance the
weight loss from unloading cargo and loss of fuel. Ballast water from somewhere in Eurasia
containing zebra mussel larvae was deposited in the Great Lakes, initiating the invasion of Zebra
Mussels in North America (Johnson and Padilla, 1996). Once established, adult zebra mussels
were able to travel throughout the Great Lakes through currents or attaching to traveling boats
(Charlebois, N.d.). In 1986, the zebra mussel population was small. By 1988, the population
had dramatically increased in Lake Erie, covering infrastructure such as the natural gas well and
water treatment plant (Carlton, 2008). There was immediate concern over the effects of this
invasive species on the health of the Great Lakes water system (Zorpette, 1996). Zebra mussels
have greatly increased in population and area occupied since introduction into the Great Lakes,
2
appearing in two provinces in Canada and many states in the US (Johnson and Padilla, 1996).
Recreational boating appears to be the main contributor to the spread of zebra mussels in North
America (Johnson and Padilla, 1996).
Problems Associated with Zebra Mussels
When examining the direct effects of the zebra mussel invasion, there appear to be many
positive impacts on the Great Lakes. The filtering capabilities remove algae allowing more light
penetration causing the water vegetation to flourish. The filtering action of the zebra mussels is
seemingly undiscriminating which results in the consumption of many pollutants. In some parts
of Lake Erie the water has increased in clarity by 600 percent when compared to the same area
prior to the zebra mussel establishment (Zorpette, 1996). But these positive effects do not
compensate for the overall detrimental effect zebra mussels are having on the entire lake
ecosystem.
Environmental Issues
Food Chain
The invasion of zebra mussels has disrupted the fragile food chain of the Great Lakes.
The aggressive nature in which zebra mussels reproduce and filter feed makes them a superior
competitor to most marine species in the Great Lakes. This high population of zebra mussels
filter a large amount of water containing a high proportion of algae (Zorpette, 1996). Algae are
the base of the food chain in the lake ecosystem which many species depend on for a source of
food. This leaves lower quantity of algae for native marine species, such as native mussel
species. Zebra mussels also interrupt the activities of other mussel species in the Great Lakes by
attaching onto them, which blocks their ability to feed. Zooplankton species are consumed by
3
the zebra mussels, limiting it as a source for many Great Lakes fish species (Zorpette, 1996). As
zebra mussels consume essential food sources required by the native species and are not a
beneficial food source themselves, they are causing a decrease in populations among native
marine species and the extirpation of species including native mussels in the Great Lakes (Ref or
your idea?).
The high pollution content in zebra mussel tissue disrupts detrital and aquatic food
chains. Few marine species directly consume the zebra mussel including few fish (drums), birds
(diving ducks), and crayfish, resulting in a lower significance on the marine food web when
compared to the detrital food web. The wastes from zebra mussels contain pollutants carried in
water. Gammarids feed on these wastes. Gammarids are food for almost all fish species in the
Great Lakes (Bruner et al, 1994). Predators and scavengers consuming zebra mussel matter
(waste and carcasses) also consume the stored pollutants (Bruner et al, 1994). These harmful
pollutants are biomagnified through each additional trophic level of the food chain (Bruner et al,
1994). The high pollutant content in deceased zebra mussels and zebra mussel waste can also
create potential water quality issues when the pollutants are released during decomposition.
Spawning Sites
The large population of zebra mussels poses a threat to the reproduction of native fish
which inhabit the Great Lakes. Living zebra mussels and discarded zebra mussel shells block
space on the lake bottom that would normally be used as spawning sites by native fish species
such as the walleye. Walleye depend on limestone lake bottoms in the Great Lakes for spawning
sites (Cooley, 1991). When this area is covered with zebra mussels, the walleye are forced to
deposit eggs between zebra mussel shells (Cooley, 1991). Zebra mussels create an inhospitable
4
environment for these eggs as their dead tissue and wastes contain a high concentration of
pollutants, potentially decreasing the quality of water in the area (Cooley, 1991). These factors
reduce the fish populations of the Great Lakes.
Anthropogenic Issues
With the Great Lakes containing 21% of Earth’s freshwater, the health of these lakes is a
global concern (Fields, 2005). Besides a source of freshwater, the Great Lakes also provide for
human recreation and industry. Zebra mussels interrupt many of these human activities in the
lakes. Zebra mussels will attach to most solid surfaces available, including “fouling the water
intakes of electricity generating stations, industrial plants and municipal water treatment units”
(New Zebra Mussel Controls, 1996).
With the zebra mussels disrupting the aquatic food chain and residing in spawning sites,
the number of fish found in these lakes has been greatly reduced, negatively impacting the
fishing industry. Even fish caught are of concern for human consumption because of the
potential of contamination from zebra mussel (Zorpette, 1996).
The sharp shells of zebra mussels can also cut the feet of people who use the lake for
recreational activities (Charlebois, N.d.). The reduced fish populations in the Great Lakes will
also result in a decrease in recreational fishing. Loss of recreational activity such as fishing,
swimming, and boating in the Great Lakes will result in a loss of revenue. These negative
experiences will retard future use.
Costs
5
Controlling the zebra mussel population is a difficult and costly battle with no realistic
possibility of success. Water intake pipes infested with zebra mussels require continual removal
which, along with repair costs, can result in tens of millions of dollars in unbudgeted
expenditures per year (Cooley, 1991). The fishing industry, worth hundreds of millions of
dollars per year, has also been decimated through the decline of fish populations as a result of the
introduction of zebra mussels (Cooley, 1991). The fishing industry in Lake Erie went from $600
million prior to zebra mussel introduction to a value of $200 million in the 1990’s (Zorpette,
1996).
Controls
There are several preventative measures that may be implemented to control the zebra
mussel population in the Great Lakes. Natural predation has been limited to crayfish and a small
number of fish and bird species. Predation and the Great Lakes physical environment (habitat
suitability, depth, substrate, etc.) can have profound effect on zebra mussel size and density
(Naddafi, 2010), but they have not been effective enough to subdue the spread of zebra mussels
through the Great Lakes. The massive area of the Great Lakes creates a diverse number of
habitats. This provides a significant amount of suitable area for zebra mussels to occupy
(Naddafi, 2010).
Anthropogenic Controls
There have been innovations aimed at minimizing the effects of zebra mussels on human
activities and infrastructure. To combat zebra mussels blocking intake pipes, water is treated
with chlorine or heat (to 40°C) to cause zebra mussels to lose attachment or die (New Zebra
Mussel Controls, 1996). These methods are not suitable for large scale projects or in winter due
6
to the distance the water intake pipes are from the coast (New Zebra Mussel Controls, 1996).
Coating the pipes with a substance such as silicone which zebra mussels are unable to attach to,
using ultraviolet radiation, magnetic fields, and filters that remove solid substances from the
incoming water are methods that have been used to control zebra mussels in water intake pipes
(Filter for Removing Zebra Mussels, 1995).
Future Prevention
Zebra mussels established in the Great Lakes will be nearly impossible to completely
remove. The goal is to prevent the further geographic spread of the zebra mussels to other water
bodies in North America. There has been some movement of zebra mussels in Canada and the
United States of America, so prevention of further dispersal is receiving attention. This begins
with the recording of more information on pathways leading to the transportation of zebra
mussels and the sharing of this information globally (Johnson and Padilla, 1996). Zebra mussels
are transported to other water bodies primarily through recreational boating by attaching onto the
boat itself, settling in a boats bilge, or attaching on plants accidently carried by the boat
(Charlebois, N.d.). Educating boaters through awareness campaigns using posters, strategically
placed signs, and personnel providing information at high risk waters is important to restrict the
spread of zebra mussels (Charlebois, N.d.). Some lakes require washing, sterilizing, or isolating
boats before use in the lake to remove potential zebra mussels inadvertently attached to a boat
(Charlebois, N.d.). Individuals concerned with transporting zebra mussels with their boats can
drain all water from their boat (motors, livewells, bilge) after use, suspend the boat out of the
water using a lift, and searching the boat for zebra mussels and plants that may be harbouring
zebra mussels (Charlebois, N.d.). These practises will discourage the attachment and survival of
7
zebra mussels. Minimizing future spread of the zebra mussels will be achieved through further
research.
Conclusion
The introduction of zebra mussels into the Great Lakes is an extreme example of the
disastrous impact an invasive species can have on a body of water. In this example, zebra
mussels were introduced via shipping, which is the most common pathway for invasive species
(Molnar et al, 2008). The aggressive nature of this pest, along with their high reproductive
output, causes concern for the natural future of the Great Lakes. Zebra mussels pose a threat to
native marine species of all kinds (birds, fish, mussels) due to their competitive abilities, toxic
body tissues, and high population densities. Zebra mussels also disrupt human activities
including clogging water intake pipes for infrastructure such as water treatment plants. Although
several methods can be implemented to reduce the detrimental effects of zebra mussels in the
Great Lakes, the complete eradication of the zebra mussels from the Great Lakes is unlikely
(Molnar et al, 2008).
Future prevention of the introduction of marine invasive species must be a primary focus.
This requires a global effort to better document the introduction of invasive species, the pathway
in which invasive species are commonly introduced, and the ecological and economical impact
an invasive species has had on a particular area (Molnar et al, 2008). Better documentation will
provide information for policy makers to make informed decisions on improving current policies
(Molnar et al, 2008). As ballast water has been identified as being the major contributor to
introduction of marine invasive species, improved practises and regulations have been
implemented for the management of ballast water in the 21st century. Some of these practises
8
include an onboard ballast water treatment system, safe ballast water exchange practises
including “exclusive use of water from a public water system, or retention of ballast water on
board” (2012 Summary of Great Lakes Seaway Ballast Water Working Group, 2013), and
compliance with the many international and regional laws in effect. The Great Lakes are world
leaders in ballast water management practises (2012 Summary of Great Lakes Seaway Ballast
Water Working Group, 2013). Global documentation of marine invasive species and their
impacts will allow policy makers to identify similar geographic areas that have been negatively
affected by an invasive species and implement effective measures to reduce the risk of that same
invasive species from invading other areas (Molnar et al, 2008).
9
References
(2013). "2012 Summary of Great Lakes Seaway Ballast Water Working Group." 1-14.
Berkman, P.A., Haltuch, M.A., Tichich, E., Garton, D.W., Kennedy, G.W., Gannon, J.E.,
Mackey, S.D., Fuller, J.A., and Liebenthal, D.L. (1998). Zebra mussels invade Lake Erie
muds. Nature 393, 27-28.
Bruner, K., Fisher, S., and Landrum, P. (1994). The Role of the Zebra Mussel, Dreissena
polymorpha, In Contaminant Cycling: II. Zebra Mussel Contaminant Accumulation from
Algae and Suspended Particles, and Transfer to the Benthic Invertebrate, Gammarus
fasciatus. Journal of Great Lakes Research 20, 735-750.
Carlton, J.T. (2008). The Zebra Mussel Dreissena Polymorpha Found In North America In 1986
And 1987. Journal of Great Lakes Research 34, 770-773.
Charlebois, Patrice. (N.d.). Zebra Mussels: Questions and Answers for Inland Lake Managers.
Illinois-Indiana Sea Grant College Program, 1-4.
Cooley, J. (1991). Zebra Mussels. Journal of Great Lakes Research 16, 1-2.
Fields, S. (2005). Great Lakes Resource at Risk. Environmental Health Perspectives 113, 164173.
10
(1995). Filter for Removing Zebra Mussels. Marine Pollution Bulletin 30, 894.
Filter for removing Zebra mussels. Marine Pollution Bulletin (1995) 30, 894.
Johnson, L., and Padilla, D. (1996). Geographic Spread Of Exotic Species: Ecological Lessons
And Opportunities From The Invasion Of The Zebra Mussel Dreissena Polymorpha.
Biological Conservation 78, 23-33.
Molnar, J.L., Gamboa, R.L., Revenga, C., and Spalding, M.D. (2008). Assessing The Global
Threat Of Invasive Species To Marine Biodiversity. Frontiers in Ecology and the
Environment 6, 485-492.
Naddafi, R., Pettersson, K., and Eklöv, P. (2010). Predation And Physical Environment Structure
The Density And Population Size Structure Of Zebra Mussels. Journal of the North
American Benthological Society 29, 444-453.
(1996). New Zebra Mussel Controls. Marine Pollution Bulletin 32, 185.
Thresher, R.E., and Kuris, A.M. (2004). Options For Managing Invasive Marine Species.
Biological Invasions 6, 295-300.
(2010). Zebra Mussels. Environmental Fact Sheet, 1-3.
Zorpette, G. (1996). Mussel Mayhem, Continued. Scientific American 275, 22-23.
11