Abundance and Seasonal Trend of Dominant Chironomid Adults and Horizontal Distribution of Larvae in Eutrophic Lake Suwa, Japan

Abstract

The abundance and seasonal trend of chironomid emergence and the horizontal distribution of larvae were studied in Lake Suwa from April 1990 to December 1991. A total of 18 species of chironomid adults were captured with a light trap set up on the eastern shore of the lake, and 11 species with bottom-type emergence traps at 2.5 m water depth. Abundant species in the light trap were Chironomus plumosus, Einfeldia dissidens, Propsilocerus akamusi, Procladius choreus, and Glyptotendipes tokunagai. In particular, the former three species constituted 86% of all adults captured with the light trap. E. dissidens was first reported from this lake in the present study. C. plumosus had three emergence periods in 1990, but only two in 1991. The emergence of P. akamusi took place during October to November in both years. The emergence periods of E. dissidens, P. choreus and G. tokunagai occurred during May to October in both years without a marked emergence peak.
In a grid survey of 68 points located at intervals of ca. 250-500 m, C. plumosus larvae were mainly distributed in the profundal zone. P. akamusi larvae had the widest distribution with high densities at all stations. E. dissidens was more abundant in the littoral zone, showing significant negative correlations with water depth and loss on ignition.