Juveniele Crassostrea gigas op adulte exemplaren, Waddenzee, Texel

In November and December 2000 juvenile Pacific oysters Crassostrea gigas were discovered on adult specimens of the same species along the Wadden Sea dike on the island of Texel. These oysters were dropped there by Herring gulls. The juveniles, obviously, had settled in the summer of this year. The use of these dropped oysters was the easiest way to collect a large enough sample of juveniles (154) to estimate the size of Pacific oysters at the end of their first calendar year near Texel. Juveniles, and particularly those only a few mm long, were far more difficult to find in situ. Together with earlier data on size-Ifequency-distribution of C. gigas collected at the same locality (Cadée, 2000), we can now conclude that they grow to almost 10 mm in their first calendaryear, to 30-40 mm in their 2nd year and to 60-70 mm in their 3rd calendaryear. In the older oysters it is not possible to estimate age from size as the different year-classes tend to overlap. Moreover, annual growthbands are difficult to discem on the older shells, because these are often heavily eroded by microborers. Settlement of juveniles on adult shells may result in the construction of real oysterbanks in the Wadden Sea in the future.