OBSERVATIONS ON THE MACROBENTHOS OF LAKE-TAHOE, CALIFORNIA-NEVADA

Lake Tahoe is a large, deep, oligotrophic lake supporting a diverse an d abundant macrobenthos. Since 1904, occasional collections of benthos have been made and results reported. This paper describes the most in tensive study, which was carried out in 1962 and 1963 by the Californi a Department of Fish and Game and the Nevada Division of Wildlife. Thr ee hundred and ninety-one Ekman grab samples were collected from widel y scattered locations. The benthic invertebrate community was dominate d numerically by oligochaetes, amphipods, ostracods, and dipteran larv ae, in that order. The variety of benthic invertebrates decreased with depth. Oligochaetes, amphipods, and turbellarians were abundant in th e deepest waters. The estimated standing crop was 2500 invertebrates/m (2) with a wet weight of 6 g/m(2). The depth distribution of gastropod s, plecopterans, and pelecypods was correlated with deep-water plant b eds. Benthic invertebrates were most numerous at the two shallowest de pth zones at South Lake Tahoe and McKinney Bay. Ten invertebrates are endemic to Lake Tahoe: one free-living ostracod, two amphipods, two fr ee-living turbellarians, two plecopterans, and three oligochaetes. Fur ther studies of the Lake Tahoe macrobenthos are recommended since the existence of some species may be threatened by water quality changes a ssociated with cultural eutrophication.