OLIGOCHAETA OF LAKE TAIMYR - A PRELIMINARY SURVEY

Lake Taimyr in Siberia is northernmost among the world's large lakes: 73 degrees 40' -75 degrees 20' N, 99-106 degrees E. The lake area is u p to 4650 km(2) in summer, with a maximum depth of 26 m and a mean dep th of only 2.8 m. The ice-free period lasts about three months. The wa ter level sinks 5.5-6 m during winter, so that 85% of the bottom surfa ce is frozen into ice for some time and subjected to negative temperat ures, probably down to -20 degrees C. In artificially melted sediment samples, 75-92% of animals survived. The average summer biomass of zoo benthos is about 1 g m(-2) wet weight, a half of this being formed by Oligochaeta. Altogether 76 samples with 3742 oligochaete specimens col lected by V. N. Greze in 1943-1944 were studied. At least 14 taxa of T ubificidae, Lumbriculidae, and Enchytraeidae were found in the lake, a nd some more enchytraeids in an adjacent river. Many immature animals could not be identified to species. Naididae were completely lacking p robably due to the absence of macrovegetation. The shallow freezing zo ne is inhabited mostly by Alexandrovia ringulata. The profundal fauna is dominated by Lamprodrilus isoporus, Stylodrilus sp., and Isochaetid es sp.