Wulken op de Waddendijk

Shells of whelks Buccinum undatum containing hermit crabs Eupagurus bernhardus were found dropped by Herring gulls Larus argentatus on the dike along the Wadden Sea, Texel. Herring gulls presumably obtained this food by kleptoparasitism, stealing from eiderducks. Whelks were formely abundant in the western Wadden Sea which had an important whelk fishery, since the 1970s whelks disappeared from the western Wadden Sea, most probably due to contamination with Tributyltin (TBT) which causes imposex (the occurrence of a penis homologue in females), and inhibites reproduction. Disappearance of whelks will in the long run also influence negatively hermit crabs as they will be unable to find suitable large gastropod shells. Only the much smaller Littorina littorea shells will be available for them.