|
Years |
Zebra and Quagga Mussel (density/m2) |
Phytoplankton (µg/ml) |
Zooplankton (µg/ml) |
Cladophora Biomass (g/m2) |
Foraging Fish (kilotons) |
Lake Trout (kilotons) |
|
0 |
100 |
3 |
2 |
10 |
150 |
150 |
|
4 |
1000 |
2.5 |
1 |
100 |
100 |
100 |
|
7 |
2500 |
2 |
0.5 |
200 |
80 |
80 |
|
10 |
7500 |
1.5 |
0.25 |
600 |
50 |
50 |
|
13 |
15000 |
1 |
0.1 |
700 |
25 |
25 |
|
16 |
7500 |
1.5 |
0.2 |
243 |
40 |
40 |
|
20 |
5000 |
1.75 |
0.4 |
136 |
60 |
60 |
The Effects of Zebra and Quagga Mussels Introduced into a Freshwater Lake
Purpose
The purpose of this experiment is to find out why there are increases and decreases in the numbers of these invasive species and the implications of these changes on the ecosystem.
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Introduction
The Zebra and Quagga mussels, nearly identical both physically and in behavior, are native to Eastern Europe and are believed to have been brought to the North American Great Lakes by ships and spread further inland by boats moving within the water channels ( Harmful Aquatic Hitchhikers ). Since their introduction, these two species have extensively colonized the North American region bringing with them catastrophic consequences. They feed on planktons greatly reducing food available for various fish species causing a sharp drop in fish numbers and native mussels (Watkins et al, 2007). The effects of the invasion continue to be felt until the carrying capacity of the ecosystem is reached, unable to sustain itself and the invasive species experience a population crash. The ecological and economical impact of these invasive species has necessitated a lot of research to deal with them.
Hypothesis
The invasive Zebra and Quagga mussels will increase in number until a point then a population crash will occur.
Methods
We obtained data on Zebra and Quagga mussel distributions from researchers in the Great Lakes region. The data was used to generate sample locations and was recorded in numbers per square meter at these locations. The population densities of the mussels at each location were combined and the ArcGIS kriging function used to estimate the density of the lake as a continuous surface.
Results/Outcome
Refer to table
Discussion/Analysis
Following the results obtained, the hypothesis is accepted. The mussels increased exponentially to a point where the ecosystem was not able to support them anymore; carrying capacity. They then experienced a population crash and their numbers plummeted.
Why do you see increases and decreases in the invasive species population?
The growth of the mussels was very high in the beginning as they had just been introduced and conditions were very favorable. Being filter-feeders, they consumed the large numbers of zooplankton and phytoplankton available causing a drop in plankton numbers. Other organisms such as foraging fish and lake trout that depend on these planktons for food experience food scarcity and their numbers also drop as the planktons drop. However after reaching the population peak, the available plankton numbers decreased to a number that can no longer support the mussels and they begin dying off hence the reduction in number. The planktons due to less predation experience resurgence and so do the lake trout depending on them.
What are the implications associated with these alterations to the ecosystem as a whole?
There are both environmental and economic implications arising from this invasion. Environmentally, the invasive mussels cause other organisms in the lake to diminish such as planktons and native mussels. Bioaccumulation of contaminants in their tissues due to their filter feeding habits poses danger to fish and birds feeding on the mussels which may affect their survival. Economically, accumulation of these mussels in water intake structures causes clogging increasing maintenance costs. The mussels cause changes in the food web that result in reduction of fish numbers negatively affecting the fishing industry causing losses (Nalepa..., Fanslow .., Lang…, Lamarand ..., Cummins ..., and Carter ..., 2008).
References
Harmful Aquatic Hitchhikers : Mollusks: Zebra Mussel. Available from http://www.protectyourwaters.net/hitchhikers/mollusks_zebra_mussel.php
Nalepa, T.F., Fanslow D.L., Lang G.A, Lamarand D.B., Cummins L.G., and Carter G.S., (2008). Abundance of the amphipod Diporeia and the mussels Dreissena polymorpha and Dreissena rostriformis bugensis in Lake Michigan in 1994-1995, 2000, and 2005. NOAA Technical Memorandum GLERL-144. Ann Arbor, Michigan.
Watkins J.M., R. Dermott, S.J. Lozano, E.L. Mills, L.G. Rudstam, and J. Scharold., (2007). Evidence for remote effects of dreissenid mussels on the amphipod Diporeia : analysis of Lake Ontario benthic surveys, 1972-2003. Journal of Great Lakes Research 33(3):642-657.
