Differential recruitment of bivalve species in the northern Wadden Sea after the severe winter of 1995/96 and of subsequent milder winters

Abstract.

High recruitment of the bivalves Cerastoderma edule, Mytilus edulis, Macoma balthica and Mya arenaria in summer after severe winters is an often reported phenomenon in the Wadden Sea. After the severe winter of 1995/96 however, only Cerastoderma and Mytilus followed this pattern in the Sylt-Rømø Bight. Repeated sampling of Cerastoderma, Macoma and Mya following a severe (1995/96), a moderate (1996/97), and a mild winter (1997/98) revealed that early recruitment was highest after the mild winter. In Cerastoderma the eventual high recruitment at the end of summer 1996 was caused by reduced benthic mortality. Low recruitment of Macoma and Mya after the severe winter may have been caused by a higher susceptibility to epibenthic predation and/or a higher susceptibility to passive re-suspension than in Cerastoderma and Mytilus. In all cases, post-settlement processes were decisive for reproductive success.