Sheltered rocky shores, such as here in Old Town Bay on St Mary’s in the Isles of Scilly, support abundant and diverse communities of seaweeds.
Battered by waves and scoured by tides, Britain’s rocky shores are dramatic and impressive destinations for any budding marine biologist. The intertidal zone offers a wealth of opportunities for exploration and supports a greater diversity of marine creatures than any other coastal habitat. At low tide, rock pools and gulleys positively teem with life, and scores of crabs, molluscs and small fish await discovery.
Sheltered rocky shores, such as here in Old Town Bay on St Mary’s in the Isles of Scilly, support abundant and diverse communities of seaweeds.
SEAWEEDS GALORE
For the keen student of seaweeds, the rocky shore is the place to visit, because the vast majority of British species are found in this habitat. That is not to say that you will find every species on all rocky shores. Quite the opposite is true: while a few species are almost universal in occurrence, most have evolved to cope with different degrees of exposure to air and to wave action, and many have restricted geographical ranges, favouring either warmer southern seas or cooler northern ones. And rocky substrates are not uniformly suited to supporting seaweeds. For example, although granite is a hard rock, some forms are so easily eroded by wave action that larger seaweed species, as well as barnacles and mussels, cannot attach themselves.
A HARSH ENVIRONMENT
The battering effect of waves and tide are obviously a challenge for animals living on rocky shores. Limpets and barnacles overcome this partly by protecting themselves with a hard shell; limpets clamp themselves down using their muscular foot, while barnacles essentially glue their shells to rock. In sheltered gullies and rock pools, sea anemones are conspicuous, as are blennies, prawns and Shore Crabs. A careful search under stones may reveal other species of crabs, including retiring hermit crabs living in the empty shells of periwinkles and Dog Whelks. Many animals of rocky shores are year-round residents, but during the summer months more unusual species visit from deeper waters.
Crustaceans are well represented on rocky shores, crabs probably being the most familiar and common examples of the group. Among their numbers, the Edible Crab is the most distinctive, with its reddish shell and piecrust margin. Crabs are mainly opportunistic feeders, often scavenging dead organic matter and other tasty morsels.
BIRDLIFE OF ROCKY SHORES
While marine invertebrates can be found in abundance on rocky shores, birdlife is rather restricted. Many of the marine creatures here either attach themselves firmly to the substrate or hide in crevices or under stones at low tide. Consequently, opportunities for feeding birds are comparatively limited and it takes a specialist to make a living here. Turnstones and Oystercatchers are regularly seen, while the Purple Sandpiper is seldom found anywhere apart from rocky shores during its winter residence in Britain.
A good rock pool will harbour a wide range of plants and animals, including some sub-littoral species. These organisms survive because the pool ensures permanent inundation by sea water.
A Purple Sandpiper foraging for food on a rocky shore. This hardy species, which breeds in the Arctic and winters on our shores, is seldom found out of sight of the sea. Indifferent to breaking waves, birds use their long bills to seek out tiny periwinkles and crustaceans from rock crevices and empty barnacle shells.