Can survive in ice
Even if the common periwinkle can survive
in, most individuals usually wander into deeper water during the winter.
They do not hibernate, but their metabolic rate decreases because their
body temperature decreases to that of their surroundings.
The common periwinkle is found from the Barents Sea to Portugal
and along the Atlantic seaboard of America from Labrador to Virginia.
Eats brittle algae
The common periwinkle eats many types
of algae, but mainly short-life and fast-growing specie, i.e. sea-lettuce,
brunslick and purpurhinnor. It cannot eat large and healthy brown algae,
but dying plants that collect on the bottom, in seaweed
banks and in crevices
and depressions are often eaten.
Many fully grown perennial algae have the ability to protect
themselves from grazing periwinkles by the use of chemical repellants
or a hard calcareous skeleton, which the young (1 mm) sprouts are unable
to do. Even small larvae that have recently fallen to the bottom, i.e.
can be eaten by the grazing periwinkles. Common periwinkles even eat diatoms
and larvae. Grazing
periwinkles can be so intensive that the rock surface can appear quite
bare (devoid of algae) where they have rampaged in large numbers.
Periwinkles are often seen grazing in mucus
tracks after other snails. The reason is believed to be that
extra good food is found there. The mucus itself contains
nutritious substances, that has furthermore been enriched by
the addition of organic material being stuck in the mucus,
and of the rich microflora
that find this comfortable environment congenial.
The shell protects against crabs, fish and
Young periwinkles run a great risk of
being eaten by i.e. the common
shrimp, the shore
crab and eiders.
Large adult periwinkles are well protected in their thick shells that
can only be broken by their largest enemies.
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