POPULATION PARAMETERS OF THE LUGWORM, ARENICOLA MARINA, LIVING ON TIDAL FLATS IN THE DUTCH WADDEN SEA

Lugworms, Arenicola marina (L.), were found almost everywhere on the tidal flats of the Dutch Wadden Sea. Mean biomass amounted to about 5 g·m-2 ash-free dry weight, mean numerical density to 17 per m2 with only about one quarter of the animals being juveniles (about 1 1 2 year old). Numbers of adults and total lugworm biomass showed a maximum in a zone at 1 to 4 km from the coasts, about halfway between high- and low-water mark and at intermediate silt content of the sediment. Numerical densities as well as biomass values showed a bell-shaped relationship to both silt percentages and heights in the tidal zone. Numbers of adults were high at lower tidal levels and at a wider range of silt percentages than juveniles. Individual weights of adults increased in an off-shore direction, and were highest at low intertidal levels and in sandy sediments, where food availability was below average. During their first period of burrowed life (April or May to winter) lugworms were most numerous on high grounds near the coast. They dispersed during winter at an age of 1 to 1 1 2 year (at a mean weight of about 40 mg ADW), transported by tidal currents. During a 10 year study of Balgzand, a 50 km2 tidal flat area in the westernmost part of the Wadden Sea, lugworm numbers were found to decline at a mean annual rate of 22%. Annuel recruitment of 1 to 1 1 2 year old juveniles to the adult stock was irregular but on average (20%) almost equal to annual mortality. After an initial decline during some years of low recruitment, total population of adults was found to be stable. Population stability will have been enhanced by a long lifespan and an inverse relationship between adult density and rate of recruitment. From data on annual elimination by mortality plus predation on regenerating tail ends, a P/B ratio of almost 0.7 could be estimated for somatic production by a stable lugworm population; to include gametic production this figure will have to be raised to about 1.0. © 1979.