Caddisfly community in the Seta-Uji River, the outlet of Lake Biwa

Abstract

Adult caddisflies were collected using light traps to investigate invertebrate habitat features in the Seta-Uji River, the outlet of Lake Biwa. Four hydropsychid and two psychomiid species were dominant in frequency and number, whereas many species common to Japanese rivers were absent. Based on the number of species in each caddisfly family, filter-feeders, which feed on lake-derived plankton, and net-spinners, which prefer stable substrates, were more dominant. Shredders/collectors that feed on deposited detritus, and case-holders, which require sand, were less dominant. The plankton supply, stable lake-outlet flow, and scarcity of lentic habitat were reflected in the caddisfly community. Occurrence differed among species, even within the same genus. Species that were abundant in the Seta-Uji River tended to be the same as those distributed mainly in the middle and lower sections of river continua, whereas the absent species tended to be the same as those distributed mainly in the upper or all longitudinal sections. As Lake Biwa separates the outlet of the Seta-Uji River from its upper reaches, some species may be unable to maintain their populations in the Seta-Uji River without an upper source of individuals. The location of the lake may explain the differences in the caddisfly community between the Seta-Uji River and other lake-outlet rivers.