Effects of the severe winter 1995/96 on the benthic macrofauna of the Wadden Sea and the coastal North Sea near the island of Sylt

Abstract.

The development of benthic macrofauna in the Wadden Sea and in the coastal North Sea after the severe winter of 1995/96 is compared with the preceding years with mild to moderate winters. In the intertidal of the Wadden Sea, ice-drift and low temperature caused the expected changes in species composition by increasing winter mortality in sensitive species, and by exceptionally high recruitment of some species during the succeeding summer. In the shallow subtidal (10–20 m depth), similar winter effects were observed. However, recovery of many subtidal populations was still incomplete until the summer of 1997. It is suggested that this was due to hydrographic conditions that carried many larvae or drifting juveniles into more distant offshore areas. This may have limited larval supply and may have delayed recovery at the onshore sites. Since in the eastern North Sea severe winters are accompanied by frequent easterly winds, it is not clear whether decreasing winter abundances in some species were due to increased mortality, or to a seaward dislocation of organisms.