Ref ID : 6598
Peter Newrkla and Specy Mutayoba; Why and where do oligochaetes hide their cocoons? Hydrobiologia 155:171-178, 1987
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In Mondsee, a prealpine lake of Austria, abundance and vertical distribution of oligochaetes were investigated at four different depths (5, 10, 20 and 40 m). Adult oligochaetes and cocoons were found to be almost always absent in the uppermost centimeters of sediment. A hypothesis was developed that predation by fish is one factor, among others, inducing the observed vertical distribution patterns. In the laboratory the predation efficiency of the fish Abramis brama decreased with increasing sediment cover over the cocoons. Tolerance limits of embryonic worms to anaerobic conditions (LC50 values) were found to differ for different developmental stages, ranging from 28 hrs for eggs to 43 hrs for fully developed embryos. Oxygen uptake rates of oligochaete embryos increased with their stages of development, eggs using 1.51 and fully developed embryos 3.32 nl O2/ind./hr (10 degrees C).