Seasonal Patterns in Lipid Content of Lake Michigan Macroinvertebrates

Abstract

Lipids in several taxa of macroinvertebrates from Lake Michigan were determined seasonally to help define the role of these animals in transfering energy in thelake. Ranges of mean lipid content relative to ash-free dry weight (AFDW) throughout the year were as follows: amphipods (Pontoporeia hoyi), 21-54%; lumbriculid oligochaetes (Stylodrilus heringianus), 12-19%; tubificid oligochaetes, 9-22%; chironomid larvae, 9-39%; and Mysis relicta, 26-37%. A pattern of increasing lipid content during spring was observed for P. hoyi, chironomids, and M. relicta, but seasonal changes were not apparent for oligochaetes. Excluding M.relicta, P. hoyi accounted for about 65% of the biomass and 70% of the energycontained in southern Lake Michigan benthic macroinvertebrates and may assimilate up to 30% of the total bioavailable organic detritus settling into the offshore hypolimnion. Calculation of the predation loss rate (production rate minus nonpredatory death rate) of P. hoyi indicated that about 13000 cal .cntdot. m-2 (2.1 g AFDW .cntdot. m-2) of this amphipod may be consumed annually by fish and other predators in southern Lake Michigan.