Plankton Studies of Lake Michigan I. Seventeen Years of Plankton Data Collected at Chicago, Illinois

Abstract

Plankton records representing>12,000 individual samples collected during 17 yrs. (1926-42) from Lake Michigan at Chicago, Illinois, were analyzed. A total of 223 different organisms were reported. A survey of all known publications on L. Michigan plankton yielded a list of 363 genera and 784 spp. and vars. The diatoms occurred in the widest variety of forms, claiming 316 different kinds; Protozoa, 182; Green algae, 124; Rotifera, 67; Blue-green algae, 39; Crustacea, 37; Miscellaneous group, 12; and Schizomycetes, 7. Quantitatively, the diatoms dominated the plankton regardless of year or season. They accounted for 90% of the average total plankton, the Protozoa produced 6%> and a miscellaneous group, which included the Blue-green algae, was responsible for 3%. The Chlorophyceae produced about 1% and the Rotifera and Crustacea rarely produced significant percentage yields. Fragilaria, Tabellaria, Asterionella and Synedra produced 34, 20, 19 and 10% or 83 of the 90% attributed to the diatoms as a group. High and low productive yrs. among the individual diatom genera were noted. Between 1926 and 1938 such fluctuations in yield followed a biennial pattern in which 2 rather low productive yrs. were followed by 2 rather high productive yrs. which, in turn, were followed by low production. From 1938 through 1942, the total plankton produced annually continued increasing without reverting to any of the previous low productive levels. 1942 produced the maximum annual average yield of the 17 yrs. covered, but subsequent yrs. have produced even higher annual av. yields. The end of L. Michigan was suspected as the cause for the increased productivity of the plankton organisms at Chicago.