Ref ID : 2380
Wilfried Schonborn; [Die okologische Rolle der Gattung Nais (Oligochaeta) in der Saale] (The Ecological Role of the Genus Nais (Oligochaeta) in the River Saale). Zool.Anz.,Jena 215(5/6):311-328, 1985
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In the river Saale near the village Rothenstein (GDR, Thuringia) the density, biomass, annual and daily production, reproduction, mortality, food, feeding behaviour, time of digestion and annual consumption of the Nais-populations were investigated. The density and production were estimated on slides and in special "production-chambers", which were exposed in the polluted river. The dominant species is N. elinguis, succeeded by N. barbata, N. communis and N. pseudobtusa. The density oscillated in the month I-VI. The greatest numbers occurred in April (32,500 m-2). In the other half of the year (VII-XII) the density is very low. The favoured habitats are stones, sticks, rubbish and submerged plants (especially Cladophora). In the Saale the asexual reproduction of Nais spp. predominates. The estimations of production in the present paper exclusively refer to asexual reproduction. In June few mature individuals of N. elinguis were found. In the experiments temperature influenced the asexual reproduction, but in the river other factors interfere with temperature (food, density, predation, endogenous factors). In the river the average generation time in the exposed chambers was 14.8 days (min.: 5.1 days; max.: >30 days). The body lengths of spring worms are significantly divergent from those of autumn, but there is no statistical significance between the body of N. elinguis and N. barbata in autumn. The average body weight amounted to 0.22 mg (N. elinguis). The values of the diverse characteristics of production are: Annual production 216.5x10E3 m-2 =47,630 mg wet wt.=223 kJ (in accordance with the ciliates and Chaetogaster production). Maximum daily production 3,607 m-2 =793.5 mg wet wt. P/B (a)=38. Mortality 52%/12.2 days (=4.3% day-1). The autumn clones are especially shortlived. The species of Nais in the Saale mainly eat detritus (1.0 l m-2 yr-1). The gut filling time average 22.6 min, the gut retention time was 29.2 min at +20 degrees C. With the help of informations from the literature it is possible to calculate that Nais spp. in the Saale can digest ~280 g bacteria/m-2/yr-1, included in detritus. Main predator is Erpobdella octoculata. In general, it would seen that Nais (together with ciliates) stimulate the growth rate of the bacteria in the detritus layers of the habitats in the polluted river.