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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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