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RESEARCH PRODUCT

The Chironomidae (Diptera) in Two Polyhumic Reservoirs in Western Finland

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ABSTRACT Composition and distribution of chironomid and other benthic fauna was studied at two adjacent 15 years old polyhumic reservoirs in western Finland by taking benthic and emergence samples. The littoral (0.5 m) coarse debris habitats, previously coniferous forest, had considerably less chironomid larvae (6–7 types, maximally 800 individuals or 0.1 g, AFDW/m2) than the mossgrown habitats, previously peatland (9–10 types, maximally 4000 individuals or 3·4 g/m2). The Chironomus larvae which were dominant at the moss sites were almost lacking at the coarse debris sites. Zalutschia zalutschicola Lipina and Tonytarsus larvae were found only at the deepest areas at 6 m. Altogether 17 species emerged from the shallow (1 m) moss habitats which were dried and frozen in late winter. Ablabesmyia phatta (Eggert), Psectrocladius edwardsi Brund., P. psilopterus K., Chironomus cf. longistylus Goetgh., Ch. macani Freeman and Limnochironomus lobiger K. were considered as characteristic species for such habitats. The three first-mentioned species seemed to be sensitive to a complete oxygen deficiency prevailing for three months in winter in one of the two reservoirs.