Rock pools

Patricia Ash

A rocky shore is a wild place at low tide, and worth exploring, but tread carefully to avoid slipping.

You can explore the rich diversity of life on rocky shores by studying life in rock pools.

You can view rock pools through the bottom of a small plastic aquarium pushed into the water, and use a pocket guide to seashore life for identifying animals and seaweeds.

Characteristic communities of animals and seaweeds are found in particular zones of a rocky shore. See how many you can find. The upper ‘splash’ zone, is relatively dry. A few shore species survive there, including black lichen, rough and small periwinkles and the sea slater, which resembles a large woodlouse.

Below the splash zone, the upper shore is flooded only by the highest spring tides. The brown seaweed, channelled wrack, survives on the rocks and green seaweeds, including sea lettuce are found in rock pools. Few animals survive the harsh conditions in upper shore rock pools as the water becomes hot on sunny days and more salty with evaporation, but is diluted by rain water. You might see small crustaceans and red beadlet anemones, but little else.

Creative Commons Image BillLarnach via Flickr

Sea lettuce [Image: BillLarnach - CC-BY-NC-ND licence]

The middle shore is characterised by barnacle-encrusted rocks and beds of mussels. Both species feed by filtering small particles out of the water. Brown seaweeds are abundant, including spiral wrack, bladder wrack and knotted wrack, protected from drying out at low tide by jelly-like mucilage. Brightly-coloured flat periwinkles, painted top shells, and crabs shelter in seaweed at low tide.

Middle shore rock pools contain a diversity of life, including red seaweeds, and breadcrumb sponges that encrust the surfaces of submerged rock. Sea lemons (bizarre sea slugs) eat breadcrumb sponges. Hermit crabs, periwinkles, snakelocks anemones, prawns and fish - including blennies, gobies, suckers and wrasse - may be seen.

The lower shore, or laminarian (kelp) zone is exposed to air for the shortest time each day. Typical seaweeds found there are large kelps, with long thick stalks known as ‘stipes’ and a strong holdfast anchoring the seaweed to rock. Marine worms live in the holdfasts, and other animals shelter in holdfasts at low tide.

Lower shore rock pools may have sea squirts and cowries and also marooned starfish, crabs and sea urchins.

Enjoy your study of life in rock pools!

This article was originally published in Summer 2005 as part of the Coast postcard pack