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Life on the Mid Shore
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It is the ready availability of refuges that
makes Kimmeridge Bay a favourite site for sea creatures,
and therefore for marine life spotters. The cementstone ledges which
project into the bay provide shady corners and a multitude of cracks,
caves and crevices. The Washing Ledge is the best example of these
and provides a convenient means of studying some of the shyer creatures.
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The best known of all tidal refugees, and the easiest to find,
is the shore crab. Beneath rocks and seaweed it is safe from
the weather and from predators (a hungry gull would soon spot a
crab in the open).
The crab's tough "suit of armour"
provides considerable protection but unfortunately neither grows
or stretches. When things get too tight, the crab, already kitted
out with a new, flexible skin, cleverly extricates itself from the
old armour. These empty "shells" are frequently found
in pools and on the shore during the summer, often mistaken for
dead crabs rather than as the cast-offs they really are. |
Shore crab (Carcinus maenas)
hiding underneath Saw Wrack (Fucus serratus) |
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The new skin will harden over the next few
days (if the crab survives this vulnerable stage), but first the
crab "balloons" itself up with water, stretching the skin
to create a bit of growing space.
In late summer an army of "baby"
crabs appears on the shore. They are not as young as they appear
- like barnacles, crabs spend the first months of their life as
free-swimming larvae (looking as much like a crab as a caterpillar
does a butterfly) before assuming their usual crawling form and
settling on the shore. |
Peering under the overhanging ledges along Washing Ledge when the
tide is out can reveal some surprises - you might find a fish returning
your gaze. The common blenny or shanny is so well
adapted for life on the shore that it can survive long periods out
of water, breathing through its scaleless skin. It frequently takes
refuge in small caves and crevices left behind by the falling tide.
If you stand your ground as the tide comes in
and look over into the water alongside the ledge, suddenly blennies
seem to appear everywhere as they come out of hiding. |
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They possess a formidable set of jaws and teeth
- designed for crushing crabs and biting barnacles off rocks. Young blennies,
such as appear in almost all the rock pools in late summer, find the shell
of an adult barnacle too great a challenge, but, not to be done out of
a meal, will wait until the barnacle starts feeding and then bite its
legs off.
The brown seaweeds bladder wrack and saw
wrack form an almost complete cover over much of the horizontal surface
of the ledges. The two seaweeds occupy different levels on the shore,
bladder wrack surviving higher up, but there is no gap between the zones.
The plants lie flat when the tide is out and the
surface layer can soon become dry and crispy. Below, however, the seaweed
remains cool and damp. Many more delicate seaweeds take advantage of the
shelter provided by the wracks.
Here you can find small red seaweeds such as pepper
dulse (well worth a nibble) and Irish moss and the rock itself
is often covered with a pink paint-like layer of stony encrusting seaweed,
which is also found lining rock pools and covers much of the shore just
below the low water mark. Here, it is restricted to areas where it will
not dry out.
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Egg wrack is a large seaweed which occupies much the same
level on the shore as bladder wrack yet has a very restricted distribution
at Kimmeridge. This seaweed cannot cope with more than a moderate
level of wave action and is therefore absent from the ledges in
the bay. Inside the remains of the old breakwater on the east side
of the bay there is enough shelter for this plant to flourish.
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The often brightly coloured flat winkle is easily spotted
browsing the wracks. The vivid yellow variety is the most noticeable
but the shells also come in reds, greens and browns.
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Both flat winkles and edible winkles fall occasional
prey to the dog whelk, though its preferred food is barnacles.
The dog whelk is able to bore through the shells of its prey (this may
take all day) then inject a narcotic. The chemical used turns deep purple
on exposure to air and the dog whelk had been the basis of a small dyeing
industry in Ireland. Related snails supported a much larger dyeing industry
in the Mediterranean producing the "Tyrian Purple" of the Ancients.
The unfortunate winkle is then digested in its shell, the resulting "soup"
being sucked up by the predator, which may take as long to consume the
prey as to bore through the shell.
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