Scuds and Mussels

Summary: Data presented here is the result of scientific studies if the bottom (benthic area) of Lake Michigan in 1994-1995, 2000, and 2005. Scientists examined the trends in abundances of Diporeia, a native amphipod with invasive zebra and quagga mussels.

Amphipod and Mussels Data Set

There are three spreadsheets: 1994-1995, 2000, and 2005

Suggestions: Comparisons can be made from place to place, year to year and among seasons.

View the Data: Data Set Scuds and Mussels Lake Michigan

General Questions:

  • What are the trends in a single population of benthic macroinvertebrates over time (temporal)? Hint: Look at trends for a single site and single species over time.
  • Are benthic species distributed uniformly over the lake bottom? Look at the distribution of a single species over space for one year.
  • Does the pattern of species distribution change over time? How does the distribution of an invasive species change over time? Look at the changes in spatial patterns — e.g., map over time for a single species.
  • Does species dominance shift during the course of an invasion? Create a series of pie charts for these three key species for a single site representing the decade.
  • Is there any evidence suggesting that zebra (or quagga) mussels affected the distribution of the native Diporeia? Is there a correlation between abundances of Diporeia and zebra or quagga mussels?
  • Do similar species show similar patterns of invasion? Is there evidence that the later invasion of quagga mussels impacted zebra mussels? Is there a correlation between abundances of zebra and quagga mussels?
  • Are spatial patterns in distributions of any or all of these three species related to water depth? Distance from shore?
  • Are similar patterns apparent in other benthic species?

Note: For a question to be testable, the locality, time and variables must be specific.

Data source: Nalepa, T., Abundances of the Amphipod Diporeia spp. and the Mussels Dreissena polymorpha and Dreissena rostriformis bugensis in Lake Michigan.

Background About Invasive Species

After the zebra mussel invaded the Great Lakes in 1989, the study found major changes in the benthic community in the early 1990’s. The study was originally intented to only take place in the southern basin of Lake Michigan, but the scientists expanded the study in 1994-1995 to look at the entire lake. After 1994-1995, lake wide monitoring of Diporeia and the zebra and quagga mussel populations continued at 5 year intervals.

Diporeia is a tiny shrimp-like organism also known as a scud. It historically is the dominant benthic invertebrate in the Great Lakes. They live in the mud of the bottom of the lakes and feed on settling algae, mainly Diatoms (a phytoplankton). Diporeia historically made up 70% of the living biomass on the bottom of the Great Lakes. When looking at the Great Lakes food chain, Diporeia is near the bottom (a primary consumer), an abundant and important food source for many fish.

Zebra and quagga mussels (collectively Dreissenid mussels) are invasive species from the Ponto-Caspian region (Black, Caspian, and Azov Seas). Zebra mussels were discovered in Lake Michigan in 1989, quaggas in 1997. The mussels arrived in the Great Lakes from ballast water being dumped into the lakes from commercial cargo ships from the Baltic Sea (which is connected via rivers and canals to the Ponto-Caspian). Dreissenids spread into all five of the Great Lakes so quickly because they reproduce at a rapid rate, adapt easily, and have tiny larvae that can hitchhike from lake-to-lake attached to boats, trailers, scuba gear, etc that are moving from one lake to another. Zebra and quagga mussels differ in appearance in that the quagga mussel is a paler color, slightly bigger at maturity, and rounder. Zebra and quagga mussels filter feed; they suck in water, take in the nutrients, and spit the bad stuff out. Their diet consists of phytoplankton, mainly diatoms.

Learn More About Aquatic Invasive Species