Estimates of Macroinvertebrate Biomass in Lake Michigan

To obtain updated, more accurate estimates of macroinvertebrate standing stocks in Lake Michigan, benthic biomass (ash-free dry weight) was determined at 40 stations in the southern end of the lake in 1980 and 1981. Biomass generally increased as sampling depth increased from 16 to 30 m, peaked at depths of 30-40 m, and then declined at depths greater than 40 m. Mean total biomass at the 16-30 m, 31-50 m, 51-90, and> 90 m depth intervals was 4.9, 7.8,4.2, and 1.9 g m·2, respectively. Oligochaetes (46%) and Pontoporeia hoyi (44%) accounted for most of the biomass at depths shallower than 30 m, but P. hoyi was the dominant form (65%) at depths greater than 30 m. Differences in total biomass between years and seasons (spring, summer, fall) were not sig"ificant, but year x season interaction was significant at depths greater than 30 m. Mean biomass in the profundal of southern Lake Michigan (> 90 m) was over twice that found in the profundal of either Lakes Superior, Huron, or Ontario. ADDITIONAL INDEX WORDS: Standing stocks, macrobenthos, benthic fauna.