The art of eating mussels

When a whelk finds a mussel, it places the foremost part of its foot along the edge of the opening between the two shell halves. When the mussel opens its shell, the whelk quickly inserts its siphon, thus hindering its prey from closing its shell. When the shell opening is large enough, the whelk with its rasp tongue tears loose parts of the soft tissue in the mussel. This process is accomplished quite quickly, a medium sized whelk of about
4-5cm can eat a cockle that is 3cm long. In a Laboratory environment, a whelk has been seen to eat two cockles within a week, but they can survive without food for several months.

Prey that defends itself

Sometimes, the whelks prey can show some resistance. Certain mussels, e.g. the blue mussel, closes its shell when the whelk goes to attack. After a while, sometimes over half an hour, the mussel opens it shell and the waiting whelk makes use of this. While the mussels shell is closed it cannot breath normally, its ability to stay closed is dependent of its ability to tolerate low oxygen concentrations. Those specie that can keep closed for longer periods probably have a lower metabolic rate. Some mussels can keep closed long enough for the whelk to give up and go away. It is therefore not unexpected that whelks prefer weak or dead mussels that give little resistance. Mussels that do not close their shells properly or like the razor clam, have a small opening between the shell halves are more prone to attack. There are however ways of protection against the whelk; some specie such as the sand groper dig down deep into the sediment where the whelk cannot reach them, the scallop retreats with the use of powerful movements of its shell, while the cockle hops away using its powerful fot.


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Bo Johannesson | Martin Larsvik | Lars-Ove Loo | Helena Samuelsson