Characteristics and Potential Causes of Declining Diporeia spp. Populations in Southern Lake Michiganand Saginaw Bay, Lake Huron

Abstract

Populations of the amphipods Diporeia spp. are declining in all of the Great Lakes except Lake Superior. We examine characteristics and potential causes of declines in southern Lake Michigan and outer Saginaw Bay, Lake Huron. Amphipod populations began to decline within 3-4 years after zebra mussels (Dreissena polymorpha) colonized both areas. In Lake Michigan, which was better studied, the decline occurred first in shallow waters (<30 m) and then progressed deeper (51-90 m). Between 19801981 (pre-Dreissena) and 1998-1999 (post-Dreissena), densities at sites in these two depth intervals declined 92%