Zebra Mussels
Student Worksheet

Lesson Introduction

Impact of Exotic Species on Lake Ecology

Zebra Mussels (Dreissena polymorpha)
Zebra mussels, a European species, were first discovered in Lake St. Clair (Detroit) in June 1988 and brought into the U.S. accidentally through the ballast water of ocean traveling ships. They are now well established in North America. Zebra mussels were first detected in Seneca Lake during the summer of 1992. They apparently made their way from Lake St. Clair. They are notorious for filter-feeding large volumes of algae or phytoplankton each day. They also colonize "new" territory quickly due to their planktonic (free-floating) larval stage, prolific reproduction (females can lay over one million eggs in a spawning season) and lack of predators in this part of the world. They quickly colonized Seneca Lake, and were well established by 1995.
Source: John Halfman, HWS, Science on Seneca

Chlorophyll a and Zebra Mussels
Chlorophyll is the pigment that allows plants to convert sunlight into energy through photosynthesis. It is found in the chloroplast's of plants including phytoplankton or algae. Chlorophyll-a is the parameter that is measured to provide an indication of the mass of phytoplankton in a waterbody. Phytoplankton are an important part of the aquatic food web because they are the primary producers of food for zooplankton and foraging fish. Without adequate phytoplankton, the food web in an aquatic system would collapse. When zebra mussels are introduced into a waterbody such as Seneca Lake they can impact this food web by competing for food with other organisms that depend on the phytoplankton. Chart A below illustrates the disruption that zebra mussels may have on the food web. Their long-term impact on the fishery is not known.

Lesson Objectives

In this lesson you are asked to graph data that show Chlorophyll a (Chl a) and secchi disk concentrations in Seneca Lake from the years 1991-2006. You will be asked to use this graph and other examples to explain some of the ecological changes that may be occurring in Seneca Lake since the zebra mussel's introduction to this waterbody. You will then answer the questions A-D using your graph and the information from the web site references listed below. At the end of this lesson you should have:

• A line graph: Average Chl a and Secchi Disk Depths Seneca Lake
• Answered questions A-D

Activity

Link to Activity 1

References

Below are web sites that provide more information about zebra mussels and their impact on lake ecology.

Why Measure Chlorophyll a ?
Learn More About Secchi Measurements
USGS Fact Sheets
Zebra Mussels and Cayuga Lake