Notes on the Vertical Distribution of Organisms in the Profundal Sediments of Douglas Lake, Michigan

Abstract

90 vertical core samples were taken from the pro-fundal sediments of Douglas Lake, Mich, during Aug. 1950. Cores were sectioned at intervals and the animals present in each stratum were recorded. 8 microbenthic ssp. were identified, the smaller ssp. not retained by a number 80 sieve being lost. More microbenthic spp. occurred in upper profundal depths (16 m.) than in deeper regions (19.5 m.). Encysted Cyclops bicuspidatus thomasi were found deeper in the sediments than other microscopic spp., being present more than 16 cm. below the ooze surface. 106 macrobenthic organisms, representing at least 5 spp. were present in the samples. These were predominantly Limnodrilus spp. The second most abundant macrobenthic form was Tendipes plumosus. More than 93% of the macrobenthos was in the upper 14 cm. of the bottom deposits, with the 1-2 cm. level containing more individuals than any other single stratum. The deepest penetration (Limnodrilus) was the 20-24 cm. stratum.