Mortality of the Pacific Oyster (Crassostrea gigas, Thunberg, 1793) in 2006 at the East Frisian coast, Germany, North Sea

Since 1998 the Pacific oyster Crassostrea gigas (C. gigas) has spread widely across the East Frisian Wadden Sea. Summer mortality of C. gigas was observed for the first time in 2005, in this area. In this study mortality data of the oyster, during summer 2006, are presented. The mortality reached all locations where C. gigas was present and in most cases these values were higher than 50% (up to 100% in some locations). Many theories have come up to explain the summer mortality of the Pacific oyster in other regions, based on different environmental factors. The causes for the mortalities in the German part of the Wadden Sea 2005 and 2006 are not yet cleared. C. gigas represents the majority of biomass in the study area, yet apart from one study (Watermann et al. 2008) no publications have been made to discuss this phenomenon. The impact on the population is discussed. If a pathogen is the causative agent of the observed mortality transmission to other molluscs and humans has to be considered.