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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Ref ID : 2311

Wilfried Schonborn; [Die okologische Rolle von Erpobdella octoculata (L.) (Hirudinea: Erpobdellidae) in einem abwasserbelasteten Fluss (Saale)] (The Ecological Role of Erpobdella octoculata (L.) (Hirundinea: Erpobdellidae) in a Polluted River (Saale)). Zool.Jb.Syst. 112:477-494, 1985

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In the polluted river Saale near the village Rothenstein (GDR, Thuringia), the ecological role of Erpobdella octoculata (L.) was investigated. The production of leeches in this section of the river is uncommonly high (=39.1 g dry wt m-2 (stones) yr-1 =19.9 gC-org =254 g wet wt =825 kJ). The leeches are (probably) biennial with breeding and dying at the end of their second year. In laboratory feeding experiments, very young leeches consumed up to 22% of their own weight per day, leeches with a weight of 30 mg only 9%. The average stay of the prey in the guts amounted to 7.8 hr. In each 24-hr-period the leeches made 7-8 rests between their catches; the rests take of an average 3.26 hr. In the 254 gut analysis (concerning all weight-classes in all months) chironomid larvae (67%), Nais (10%), Tubificidae (above all Limnodrilus hoffmeisteri) and Lumbriculidae (7.9%), Chaetogaster (0.4%), and other prey (14.6%) were found. In winter most leeches had empty guts. The composition of prey in the guts shows seasonal fluctuations. The average number of prey per leech was in the range of 1.26 (first weight-class) to 11.8 (last weight-class), and the average weight of gut content per leech amounted to 1.18 mg wet wt. The capture of big chironomid larvae increases with increasing age. The annual consumption of leeches/m-2 amounted to 1,500 g wet wt (calculated from feeding experiments) or 1,000 g wet wt (calculated from gut analysis). The gut analysis seems to give real values for the river. E. octoculata is a member of the main food chain: bacteria/diatoms/unicellular algae - Ciliata - Chaetogaster - Erpobdella - fish, and of the short detritivorous chains: Nais/tubificids/chironomids - fish. First fed erpobdellids only in a small number; the most losses of leeches occurred by drying or drift. The leeches capture their prey in nearly 5 habitats of the river (stones, sticks, sediment, water-plants, and rubbish). Therefore, the high density under stones during the day is an effect of concentration. Feeding was most intense at night (in darkness). E. octoculata is in the river Saale a centre of predation with features of a final consumer, depending on the structure of the river-bed.