Exploring Abiotic Changes due to Zebra Mussels

Engage

1. Ask: Did any organism’s population decline as a result of zebra mussel invasion?  Return to the food web diagrams from the first day and use that to keep track of which organisms have experienced population changes.  Alternatively, project the "Sharing Results" chart found in the student worksheet from Day 2. 
2. “Expert groups” from the previous lesson’s Jigsaw activity should present their findings to the class. They should share the following:

a.      If their organism’s population declined or increased.
b.      Why this population change might have occurred.
c.       How confident they are with their conclusion. 

Explore

1. Make a list on the board of abiotic characteristics of the Hudson River ecosystem. Students should share their predictions about what abiotic factors will be affected, either directly or indirectly, by the zebra mussel invasion.  
2. Hand out the worksheet “Exploring Abiotic Changes”.  Ask students to complete Part 1: Abiotic Factors individually or in pairs. 
3. Students will read AMNH passage 3: Short Term Impacts of Zebra Mussel Invasion.
4. Students will watch video 3 to confirm if their predictions about the abiotic factors were reflected in the data collected by scientists. Students should complete Part 2 of the worksheet: Ecosystem Changes. 
5. Review student answers about both biotic and abiotic changes using the chart on the worksheet. 
6. View video 4, which highlights how the river may continue to change as a result of the zebra mussel invasion; students should complete Part 3 of the worksheet: The Future.
7. Finally, students should complete Part 4: Making Connections.  This can be done individually or in groups.
8. The videos suggest how the river may continue to change over time. Students can make additional predictions about what might happen to the system in the future. ASK: Are there any additional data the scientists ought to collect? 
9. A powerpoint is available to support this discussion – it includes several slides that depict how the different populations changed, focuses on the native freshwater mussels to explore the consequences, and highlights the connections between biotic and abiotic factors. 

Explain

The following is a summary of the results that were shared in Video 3- “Results”:

1. Zebra mussel biomass outweighs the combined biomass of all other consumers in the Hudson River.
2. Zebra mussels have been eating the majority of phytoplankton and small zooplankton, leading to the following declines:

• 80% loss of phytoplankton
• 90% loss of small zooplankton
• Total plankton fell by half- this is a reduction in fish food.
• Reduction of fish in open water (shad, herring, perch, stripe bass, bulk of fish community).
• DO down 12%- shows high activity (respiration) of zebra mussels, combined with the fact that they removed O2 producers (phytoplankton)

The following is a summary of the results that were shared in Video 4 “The Future”:

Over time, zebra mussels are decreasing in size.  Significance: the size of mussels determines what they can and can’t eat. Smaller zebra mussels cannot eat zooplankton. Accordingly, zooplankton populations are recovering. In addition, the lifespan of mussels is shorter. Scientists are uncertain, but they believe that predators like blue crabs or pumpkinseed fish may be playing a role.

Take Home Messages:

1. The abiotic and biotic parts of an ecosystem are strongly connected. Changes in abiotic factors affect the biotic environment. As the results of this study show, changes in biotic factors of an environment can affect the abiotic environment, too, and those changes can affect other biota.
2. Long-term monitoring of ecosystems is important. Ecosystems are dynamic. Even the affects of a major biological invasion, (e.g. zebra mussels), can change over time.

Extend

For Homework: Read passage #4 from the AMNH website and answer questions at the end.

Evaluate

1. Review student answers to questions in Worksheet 3: Exploring abiotic conditions.
2. Students can submit their worksheets, or provide answers in a class discussion that explain how the ecosystem changed in response to the zebra mussel invasion.
3. Writing to inform prompt:

Based on what you have learned about the zebra mussel invasion, explain how the Hudson River ecosystem changed as a result.  Be sure to include both biotic and abiotic changes.