Rocky shores

At low tide, life on rocky shores shows as bands of different colours and textures. Animals and plants are arranged in distinctive zones starting at the very top of the shore with grey, yellow and black lichens, looking more like splashes of paint than plants. Much of the mid-shore is covered with a variety of brown seaweeds, arranged in bands down the shore – channelled wrack, followed by spiral wrack, then a mixture of egg wrack and bladder wrack. On the lower shore serrated wrack is often covered with small, orange sea squirts or tiny, coiled, white worm tubes. Kelp plants, large brown seaweed with wide, slippery fronds, are exposed only on the lowest tides at the very bottom of the shore.

On exposed headlands or steeper rocks this zonation is most distinctive with the upper black lichen band contrasting with the rough coat of white barnacles below interspersed with patches of dark blue mussels, often dotted with white dog whelks preying on them. Limpets cling tenaciously to the rocks, and various kinds of winkles are everywhere, grazing on larger seaweeds and the seaweed film on rocks.

Because sea lochs are so sheltered, quite small stones may remain unturned by waves and support lichen and seaweed growth. Amphipods, which are small lively relatives of prawns and shrimps occur in large numbers under stones together with green shore crabs and many other species.

Colourful sponges, sea firs and sea anemones thrive in the dampness of rock overhangs sheltered by seaweeds. Several eel-like fish are common on sea loch shores, hiding under seaweeds and stones while the tide is out. Butterfish, with their distinctive light-ringed dark spots, and viviparous (producing live young rather than eggs) blennies can be found on most shores.

Sediment shores

In most sea lochs there are areas of mud or muddy sand, where the tell-tale toothpaste-like casts of lugworms create a miniature, almost lunar landscape of mounds and craters. The intricate branched tubes of sandmason worms, beautifully built of sand grains, stick up through the sand at the bottom of the shore. Nearer the top of the shore, tiny black spire snails graze the surface of the sand or mud leaving tortuous tracks in their wake.

Other animals live buried in sand or mud. These include various bivalve molluscs, especially cockles, a range of worms, amphipods and sea potatoes (a burrowing sea urchin).

Common mussels grow to a large size, forming dense and extensive beds where freshwater streams spread out over the shingle shores, or on very shallow sills where brackish surface water flows at low tide. The extreme shelter and variable salinity characteristic of many sea lochs, provide perfect conditions for two unusual species of brown seaweed. A much-branched, almost bladderless form of egg wrack grows unattached in wig-sized clumps in places where there is no danger of removal by waves or tides. The smallest wrack of all, moss wrack, grows less than a centimetre tall at the top of very sheltered shores, giving the saltmarsh turf a gingery-brown hue from a distance.

Sandmason worm tube sticking up through the sand

Underwater life

The underwater world of sea lochs is remarkable, populated by a great diversity of strange and colourful animals and plants extending from the clear shallows of only a few metres to murky depths in excess of 200 metres where complete and utter darkness prevails. It is only recently, with the development of SCUBA diving, that the upper regions of this underwater world has been accessible but even today only a few of people have experienced the thrill of a dive. SCUBA divers cannot dive much below 50 metres and it is only very recently that technology has enabled us to explore the deeper areas using Remote Operated Vehicles (ROVs).

The large, slippery, brown kelps which can sometimes be seen on the lowest tides, mark the top edge of a great kelp forest which extends underwater all around the coast of Britain wherever there are suitable hard surfaces for the kelp to attach to.

The stiff-stemmed kelp, Cuvie Laminaria hyperborea, with its split, palm-like frond grows best in strong water movement and provides a sheltered home and food for a wide variety of marine animals and plants living on the seabed and on the kelp itself.

In the quieter waters inside sea lochs, another kelp, sugar kelp (Laminaria saccharina) with an undivided, crinkly frond, gradually takes over as the dominant species. The fronds of sugar kelp lie across the seabed, shading the silty rocks beneath. Often the rock has a crust of hard, pink coralline seaweed and animal life is confined to a few sea squirts, squat lobsters and brittlestars in crevices.