SEASONAL-VARIATION OF LIPID-COMPOSITION WEIGHT, AND LENGTH IN JUVENILE DIPOREIA SPP (AMPHIPODA) FROM LAKES MICHIGAN AND ONTARIO

Benthic amphipods, Diporeia spp., were collected during 1988 and 1989 at four sites to compare size and Lipid levels of animals living in La kes Michigan and Ontario: sites were at depths of 45 and 100 m in Lake Michigan and 35 and 125 m in Lake Ontario. In Lake Michigan, the mean length, mass, and Lipid levels of individual Diporeia from 45 m were significantly different from those collected from 100 m in 1988, in 19 89, only mass and Lipid levels were significantly different between de pths. In contrast, regardless of the year, the Lake Ontario Diporeia f rom 35 m were similar in mass and length to those from 125 m, but lipi d levels were significantly different between depths. Combined means f or total lipid for each lake over similar months revealed higher level s in Lake Ontario than in Lake Michigan Diporeia. Triacylglycerols wer e the dominant Lipid class in all the amphipods, with mean levels reac hing a maximum of 84% of the total lipid in individuals from Lake Onta rio at 35 m. Trophic state, food-web, and (or) genetic differences are probably responsible for the occurrence of higher lipid levels in Lak e Ontario Diporeia than in Lake Michigan Diporeia.