THE ABUNDANCE OF SHORE CRABS CARCINUS-MAENAS (L) ON A TIDAL FLAT IN THE WADDEN SEA AFTER COLD AND MILD WINTERS

Juvenile shore crabs Carcinus maenas (L.) living on a tidal flat in the westernmost part of the Dutch Wadden Sea were sampled frequently during the springs and summers of 1983-90 and less intensively during 1969-82. 1-yr-old crabs were more abundant during springs after mild than after cold winters, but gradually disappeared from the tidal flats during summer. Settlement of the new generation of crabs started earlier in summer by up to 6 wk (mid-June-early August) after mild than after cold winters. The lower abundance of the I-group and the later appearance of the 0-group crabs after cold winters both contributed to a positive relationship between preceding winter temperatures and crab biomass during spring and summer (March up to mid-August). The predation pressure of crabs on the tidal-flat fauna will therefore be highly variable from year to year and the paucity of crabs during the summer after a severe winter will be a contributory factor in the high reproductive success often observed in bivalves during such summers.