Rock Pools  

 

Beaches in Cornwall and the Isle of Wight are known for the rocky pools that are exposed by the retreating tide.  Look closely into them, and you will find a beautiful and fascinating collection of plants and animals.  Hiding under the ledges might be prawns, with their almost translucent bodies and ectoskeletons - a hard outer skeleton that protects the body.  Think of prawns that you buy to eat (they are somewhat larger!) - they are already cooked,  and it is the cooking process which turns their bodies pink.  Before eating, you remove the outer shell.  This shell is the skeleton.  

A variety of small fish may be found, the comical little blennies are a large family.  They skim over the bed of the pool, resting on their fins as if they were elbows, ready to dart away at the first sign of danger.  They are active fish, requiring a great deal of oxygen, and as levels of oxygen in the pool is quickly used up, they are able to leave the water, and can be seen hopping and crawling out of the pools, especially on hot days.

 

Anemones, on the other hand, have no skeletons.  They must retain moisture when the tide is out, and to do this, they close up tightly.  Their tough outer skin will dry slightly, but is constantly being shed and renewed just as ours is, and moisture is easily retained inside.  They also close up in order to ingest food into the stomach.  There are several different types of anemone to be found on British shores.

This group shows, top left, a red beadlet anemone that is just beginning to open.  It is possible that the blue beads that give it it's name are poisonous, or maybe they help attract the small fish that this creature is capable of catching.  In front is a smaller specimen of the same type, which is fully open. When completely open, the beads are hardly visible.  On the right is a strawberry anemone, just beginning to open - it's easy to see how this type got their name!

A closer look at the partly opened beadlet anemone.  These colours are true to life.  Beadlets anemones may be red, pink, brown or greenish in colour, and the beads will also from this electric blue to paler tones, even through to grey/green.

On the left, one has curled round the edge of a shell.  The part of the anemone that fixes to a rock or stone is called the foot.  It will stick VERY firmly - remember how strong the tide can be!  Now look underneath the shell, there is a young anemone there - about three weeks old.  The young are catapulted out of the centre of the parent, and must immediately try to attach themselves to a firm base, and fend for themselves.  Young and old are what is known as filter feeders - as the water sifts through the tentacles, minute organisms will be trapped on the sticky tentacles.  Only the larger specimens will trap fish.  On the right, two beadlets are closed on the underside of a rock at low tide.  Do not try to pull specimens from rocks - they will certainly be badly injured or killed.

On the left, above, is my favourite photograph.  Caught by the camera just as it began to open, the centre looks almost like a scowling face as it is slowly revealed!

On the right is a snakeslock anemone.  Looking a little like the head of Medusa, these anemones are not able to close tightly as the others do.  They usually place themselves on the bed of the sea or pool, where the water will always lie and cover them.  Shades of grey and green, the snakelocks often have pink tips to their tentacles.  They sting, and paralyze their prey, so catching more than the beadlets.  They are also able to filter feed, and produce their own food by photosynthesis - hence their green tinges, and the need for them to be in good sunlight.

 

More news from the rock pools in the summer!