3 December 2011

Whelks in abundance in the Oosterschelde

Last wednesday we spotted a lot of whelks, Buccinum undatum (NL: wulk) while diving at Stavenisse Veerweg, Oosterschelde.
Cloaked. The whelk is a beautiful snail and one of the biggest in North-West Europe. The shell is up to 11 cm long, however I have once seen a whelk of about 16 cm long in the collection of a former member of the 'Strandwerkgroep Waterweg Noord'. Because of its size I mistook it at first for a red whelk, Neptunea antiqua (NL:noordhoren).

Till a few years ago whelks were quite rare because of tributyltin-poisoning.

Because of the housing shortage for common hermit crabs, Pagurus bernhardus (NL: gewone heremietkreeft) one of the members of the 'Strandwerkgroep Waterweg Noord' collected empty snails at the Kalkbranderij at Yerseke and threw them in the tidal zone near Kattendijke. Apart from one Neptunea contraria - not the most obvious house for a hermit crab because it is contrary coiled (hence 'contraria') - we never retrieved them (which is good!).
Specimen collected at Glasjesnol, Oosterschelde. Photo in aquarium.

Whelk laying its spongy egg masses. Naylor (2005, see literature): 'After mating, the female whelk will lay a mass of up to 2000 egg capsules. Each capsule contains approximately 1000 eggs.' Fortunately the parts per million of tributyltin in the water are low enough.

The head, tentacles, mantle and siphon with typical black flecks. At the base of the tentacles the eyes can be seen.
Five whelks feeding on a dead shore crab, Carcinus maenas (NL: strandkrab).