Seasonal trends in populations of chironomid midges in the high mountain Nishina Three Lakes in Japan

摘要

Chironomidae, one of the largest groups of aquatic insects, occur in most types of freshwater habitats such as springs, streams and seepage areas, rivers, lakes, ponds, marshes, and temporary pools (Cranston 1995). Approximately 5000 species have been described world-wide (Cranston & Martin 1989). About 1000 species are known from Japan (Sasa & Kikuchi 1995), but few studies on chironomid fauna in lentic/lotic habitats have been undertaken in Japan because of the difficulty of larval species identification.rnLake Aoki (36°37'N; 137°51'E), Nakatsuna (36°36'N; 137°51'E), and Kizaki (36°33'N; 137°50'E) are called the Nishina Three Lakes and are connected by the same water system, the Nougu River (Fig. 1). Lake Aoki (surface area 1.86 km~2, altitude 822 m a.s.l., maximum depth 58.0 m) is the deepest and has the greatest water volume. Lake Nakatsunarn(surface area 0.14 km~2, 815 m a.s.l., maximum depth 12.0 m) is the smallest, and Lake Kizaki (surface area 1.40 km~2, 764 m a.s.l., maximum depth 29.5 m) is altitudinally the lowest of the lakes. Lake Aoki is oligotrophic, while Lake Nakatsuna and Lake Kizaki are mesotrophic (Tanaka 1992). These lakes provide good examples for comparative study of the composition of biota in relation to water quality criteria and trophic status because they have similar geological and climatic conditions. However, studies of the macrobenthic fauna in the littoral and hydrophyte zone, especially chironomid fauna and their seasonal abundance, have been very few. The present study was conducted to clarify the species composition and seasonal trends in the littoral and hydrophyte zones of Nishina Three Lakes.