POPULATION-DYNAMICS AND ENERGY BUDGET OF MARIONINA-SOUTHERNI (CERNOSVITOV) (ENCHYTRAEIDAE, OLIGOCHAETA) IN THE SHALLOW LITTORAL OF LAKE ESROM, DENMARK

Marionina southerni (Cernosvitov) was numerically the dominant oligoch aete in a shallow, strongly exposed surf zone locality (0-1 m depth) i n the mesotrophic Lake Esrom. It comprised 21,500 ind m-2 or nearly 50 % of the total oligochaete community, which otherwise was dominated by Nais spp. and the lumbriculid Stylodrilus heringianus Claparede. M. s outherni appears to have a 1-y life cycle. Individual biomass ranged f rom 3 to 48 mug ash free dry weight. Annual net production at the site was 5.1 kcal m-2 (size-frequency method) with a P/BBAR ratio of 2.5. This is about 0.5% of the estimated mean zoobenthic production in the littoral zone from 0 to 2 m depth in Lake Esrom. At 5-degrees-C M. sou therni showed a constant oxygen uptake down to 25% oxygen saturation, but practically no regulatory respiration was found at 20-degrees-C. I n the field M. southerni was never found in sediment with less than 60 % oxygen saturation. The annual community respiration of M. southerni was 14.2 kcal m-2, and annual assimilation thus made up 19.3 kcal m-2 with a net production efficiency of 26.5%.