Japanese oyster and Blue mussel

Blue mussel, Mytilus edulis, beds in the intertidal Wadden Sea have been partly replaced by the introduced Pacific oyster, Crassostrea gigas. The non-indigenous Pacific oyster, Crassostrea gigas, was introduced in the Easter Scheldt estuary for culturing purposes in the mid sixties. At first C. gigas was confined to the culturing sites in the Easter Scheldt estuary in the South of the Netherlands, but after some warm years it started to spread northwards and settled in the Wadden Sea on top of hard substrates. Both C. gigas and M. edulis are ecosystem engineers in sedimentary tidal flats. They provide hard substrates for sessile organisms and shelter for mobile organisms in areas dominated by soft sediments. Both species produce biodeposits and enrich the sediments with organic matters. The transformation of Mytilus –beds into Crassostrea –beds gave rise to the question what the effect of the invader would be on the native community and whether the Crassostrea –beds take over the function of Mytilus –beds in the future. In this paper the different effects of C. gigas and M. edulis on the ecosystem have been highlighted to answer the question whether Crassostrea –beds will take over the function of the Mytilus –beds as ecosystem engineer and whether this lead to an increase in biodiversity. I found that the biodiversity surrounding Crassostrea –beds is higher than the diversity surrounding Mytilus –beds, when the area was covered less than 50% with C. gigas. When the coverage was higher than 50% the diversity decreased again. With the increasing temperatures the spread of C. gigas will be facilitated, increasing the chance that the C. gigas coverage will increase to above 50% causing a decrease in biodiversity.