Preliminary Investigations for Causes of theDisappearance of Diporeia spp. from Lake Ontario

Abstract

The amphipod Diporeia spp. comprised 60-80% of the benthos in offshore Lake Ontario and was an important food for fish. In eastern Lake Ontario, Diporeia spp. began disappearing in 1993 just after the arrival of dreissenid mussels. We compared survival of Diporeia spp. and Hyalella azteca in sediments from areas where Diporeia spp. populations had vanished with survival in sediments still inhabited. Survival was also examined in the presence of zebra mussel (Dreissena polymorpha) pseudofeces, filtered water from mussel cultures, and added bacteria. The Microtox test indicated that sediment pore water was not toxic. Sediments from sites with large Dreissena spp. 1 Corresponding author: [e-mail]