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 oligochaete in a shallow, strongly exposed surf zone locality (0–1 m depth) in 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. southerni appears to have a 1-y life cycle. Individual biomass ranged from 3 to 48 µg ash free dry weight. Annual net production at the site was 5.1 kcal m−2 (size-frequency method) with a P/B 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° C M. southerni showed a constant oxygen uptake down to 25% oxygen saturation, but practically no regulatory respiration was found at 20 °C. In 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%.