Massale sterfte van Ensis directus op de Schanserwaard en elders blijft raadselachtig

A mass-mortality of the American Razorclam Ensis directus occurred during a prolonged period of November 1993 to February 1994 on a tidal flat area near Texel, Dutch Wadden Sea, and also on other places in the Wadden Sea, and along the Dutch North Sea coast. We suggest that this mortality was related to a cold period in November 1993. A less severe Ensis mortality occurred in spring 1993, probably related to a cold period in January 1993. Herring Gulls and other birds could not deplete this rich foodresource leaving rotting Ensis on the tidal flat and accumulating near the high water line (fig. 2). Ensis specimens were observed to move out of the sediment. During cold periods, such behaviour has been observed also in other bivalves. It might have survival value: although most will die, some may be transported to deeper water and survive, their offspring may repopulate the tidal flats.