Some animals live on the rocks, some underneath, and a few even live inside them.
Between the tides
In most places on the earth the sea ‘comes in’ twice a day and then recedes to leave the shore exposed. There is a strip of land (between high water and low water) where plants and animals spend some of their time in air and the rest under water. If they live near the high water mark they will spend most of their time in air, and vice versa if they are nearer the low water mark.
Different Shores
On beaches where the movement of water removes smaller particles we are left with ‘Rocky Shores’. Sometimes the shore is composed entirely of the ‘bedrock’, with no loose material sitting on the surface, but more typically there will be rocks and boulders of varying size lying on this bedrock, providing a number of different places for the animals and plants to colonise. (Sandy and muddy shores will be dealt with in subsequent articles.)
On the rocks
Any organism that lives on the bedrock or upper surface of the boulders needs to be firmly attached. Some are actually ‘cemented’ to the rock (e.g. Barnacles), while others simply ‘hold on tight’ (e.g. Limpets). The larger plants are usually brown algae (e.g. Fucus), and they can provide shelter for many animals. These algae photosynthesise, and some of the animal species graze on them directly, but the majority of creatures here browse on the much smaller organisms which establish themselves on any available surface. Many more animals ‘filter-feed’ and eat the plankton that is brought in each time the tide returns.
Under the rocks
Much more delicate animals can survive on the underside of rocks and boulders, especially if there is a little trapped water. Often delicate sponges and sea-anemones can be found alongside encrusting ‘bryozoans’ and weird arthropods. Little light reaches these places, so everything here is a filter-feeder or a predator.
In the rocks and crevices
The Piddocks are bivalve molluscs that actually burrow into softer rocks. From their safe home within these rocks they make a living by filter-feeding. When they die they leave a nice sheltered hole, and these holes (and any natural crevices in the rock) become the home of specialists known as ‘crevice fauna’.
Rock Pools
Very often there will be pools of sea-water left on the beach, and those nearer the low-water mark can trap interesting animals as the tide recedes. Some can be quite large and you need to be careful when poking around. They are usually fully aquatic animals and they will therefore not enjoy being exposed to the air, they should be observed ‘in situ’.
Turning rocks over
Once you have looked at the rock surface and in the rock pools it will become impossible to resist turning over a few of the manageable rocks to see what is lurking beneath. This will certainly expose many interesting creatures, and there is no need for it to cause lasting damage provided the rocks are carefully returned to their original position. It is absolutely essential to put them back the ‘the right way up’, and good if you can get them back to their original location. And put them down carefully – rocky shore animals are necessarily tough, but they don’t take kindly to having rocks dropped on their heads!
Other articles by John Blatchford
