SEDIMENTOLOGICAL CONTROLS ON THE DISTRIBUTION OF DIPOREIA AND DREISSENA SPECIES IN LAKE ONTARIO

The burrowing amphipod, Diporeia, has declined over the past decade from one of the most abundant benthic macroinvertebrates in the Great Lakes to very low numbers in many areas. This decline parallels and may result from the recent invasion by the exotic zebra and quagga mussels (Dreissena species) and is ecologically important because Diporeia are a vital link in the food web for game fish and the fisheries in the Great Lakes. Here, we present our continued investigation of the sedimentological controls on the distribution and abundance of Diporeia species in Lake Ontario. High-resolution seismic profiles, side-scan sonar profiles, and surface sediment samples (analyzed for grain size, total organic carbon content and carbonate content) collected in 2001 along two shore-perpendicular transects from 50 to 150 m of water offshore of Olcott and Rochester, NY, suggested that thinner and coarser postglacial muds (implying sediment resuspension and erosion) recovered from the deepest water north of Olcott appears to be a refuge for Diporeia from the invading Dreissena species (Etherington et al., 2002). The seismic profile and sediment sampling survey was extended during 2002 approximately 20 to 30 km lakeward northwest of each transect to assess the extent of the thinner postglacial muds and refuge. The results confirm minimal accumulation of postglacial muds in the deepest part of these transects. A few quagga mussels were recovered from some of these new deep water sites so that the pervasiveness of the Diporeia refuge is unclear at this time.