BIOMASS AND SPECIES RICHNESS OF THE MACROBENTHIC ANIMALS LIVING ON A TIDAL FLAT AREA IN THE DUTCH WADDEN SEA - EFFECTS OF A SEVERE WINTER

The winter of 1979 was relatively severe in the Wadden Sea area. About 90% of the winters during the last century were milder. The mean temperature during the first 3 months of 1979 was 3°C below the long-term average. The effects of the low temperatures on the macro-zoobenthos living on the tidal flats in the western part of the Wadden Sea were studied by comparing abundance and biomass estimates found in spring 1979 and survival rates during the 1979 winter with comparable values observed at the same places during the 10 preceding years. Both total biomass and species richness were reduced after the 1979 winter, but the decline was only slight. Greatest reductions were observed in areas low in the intertidal. Most of the seriously affected species show their highest densities low in the intertidal or even subtidally. The following species suffered high losses that could be related to low temperatures: the bivalves Abra tenuis, Angulus tennis, Cerastoderma edule and Mysella bidentata and the worms Lanice conchilega and Nephtys hombergii. The reduced numbers of the shrimp Crangon crangon will have been caused by enhanced emigration to deeper water. The reduced numbers of the scale-worm Harmothoe lunulata could be explained by the absence of its host Lanice conchilega. Among these species, only Cerastoderma edule contributed substantially to the total biomass in the preceding years. © 1979.