Nalepa, T. Great Lakes Environmental Research Laboratory, NOAA, nalepa@glerl.noaa.gov
Hartson, D. Cooperative Institute for Limnology and Ecosystems Research, University of Michigan, hartson@glerl.noaa.gov
Fanslow, D. Great Lakes Environmental Research Laboratory, NOAA, fanslow@glerl.noaa.gov
Lozano, S. Mid-Continent Ecology Division, EPA, lozano.stephen@epamail.epa.gov

 
TEMPORAL TRENDS IN ABUNDANCES AND PHYSIOLOGICAL CONDITION OF THE AMPHIPOD DIPOREIA IN LAKE MICHIGAN
 
The amphipod Diporeia is the dominant benthic macroinvertebrate in Lake Michigan and a keystone species in the lake's trophic structure. We have been monitoring populations in the southern basin since 1980. Beginning in the early 1990s, densities in the southeastern portion of the lake began to decline; at some sites, densities decreased from over 10,000 m-2 in 1980 to less than 100 m-2 in 1993. The decline coincided with the introduction and rapid increase in the zebra mussel, Dreissena polymorpha in this portion of the lake. Diporeia relies on freshly-settled organic matter as a food source (i. e., diatoms), while Dreissena intercepts this material before it settles to the bottom. Further, lake-wide estimates of physiological condition in late summer 1994 and 1995 showed that lipid content and length-weight of Diporeia was lowest in the southern basin. Mean lipid content of the population was only 16.3 % (of dry mass), and the weight of a standard 5-mm animal was 0.34 mg. These values are about one-half the values reported for Diporeia from the southern basin in the 1980s and , for lipid content, below the value considered a minimum for successful reproduction.
 
Day: Wednesday, Feb. 3
Time: 02:15 - 02:30pm
Location: Eldorado Hotel
 
Code: SS18WE0215E