Endangering potential of eulittoral Blue mussel beds in the Wadden Sea of Lower Saxony by the bio-invasion of the Pacific oyster (Crassostrea gigas)

In a world of increasing globalisation nearly all ecosystems become threatened or are affected by alien species. If a species become invasive this can lead to alterations in the recipient region, but the reasons for the success of an alien species and the causes of its impact remain often unclear. Since the late 1990's, the Pacific oyster has spread into the East Frisian Wadden Sea (Germany). This invasion provided the opportunity to study the population dynamic, the pattern of spread and the influence of the oyster on the ecosystem during the initial bio-invasion process. The oyster population increased significantly during the study. During the beginning invasion the distribution of oysters developed patchy, which might be due to larval dispersal and/or supply. To investigate this, a molecular method was developed to identify oyster larvae in plankton samples. The spread of the oyster on Blue mussel beds may lead to competition between both species. But, the oysters had no negative effect or outcompete the mussel. However, an influence in the Wadden Sea is to be expected, which is indicated by high biomass production and the habitat structure provided by the oyster