Human effect on unionid health after removal of Dreissena polymorpha in Douglas Lake, Michigan.

Abstract

Zebra mussels (Dreissena polymorpha) are an invasive species that is having a negative effect on the native clams (unionids) of Douglas Lake, Michigan, USA. We wanted to test if humans are helping clam fitness by cleaning off attached zebra mussels. We surveyed South Fishtail Bay, North Fishtail Bay, and around Douglas Lake Bar in Maple Bay, taking the percent coverage and mass of zebra mussels on each clam, along with the mass, length, thickness, and species of the clams found. We also built a pen in Douglas Lake with cleaned off clams in it to calculate a reattachment rate of the zebra mussels. Only two clams were found around Douglas Lake Bar, which we did not include in our statistics. However, for South and North Fishtail Bay we found significant differences for the mass of clams and the mass of zebra mussels, South Fishtail Bay having heavier clams with a smaller mass of zebra mussels attached. We concluded that humans are having a positive mpact on clam fitness when they remove zebra mussels from the shell of the clam. Zebra ussels are able to reattach themselves quickly, but if we can save the clam population of South Fishtail Bay, we may be able to save the clam population of the entire lake. im