Crassostrea gigas gevestigd op levende Littorina littorea

Among the Pacific oysters Crassostrea gigas dropped by herring gulls on the Wadden Sea dike of Texel, two oysters were found (45.5 and 68 mm in length), each of them attached to a still living periwinkle Littorina littorea, 21.3 and 22 mm in length. These littorinids had to drag an extra weight far surpassing their own. Littorinids of this length weigh on average 3.5 gram at this locality, with the oyster their weight had increased to 19 and 40 gram and their volume had increased a comparable amount. Epizoans of this size and weight could be a problem for their hosts. Data in the literature of massive growth of epizoans on vagile benthos indicate that they use their hosts usually only as a substrate that keeps them above the sediment. Sometimes epizoans may give shelter or protection to their host; for protection hermit crabs even actively add actinians to the shells they inhabit. There was no evidence that heavy overgrowth with barnacles was deleterious for L. littorea (Hertweck, 1979). The fact that oysters may reach an age of up to two years on these living L. littorea might also indicate the absence of deleterious effects.