How to recognise the plants and animals of sandy shores and rock pools, shingle beaches and estuaries
Our varied coastline is the product of thousands of years of erosion by wind and waves. Beating and tearing at the original rocks -some hard, some soft – the elements have shaped them into sheltered bays or exposed headlands, sheer cliffs or shifting sand-dunes. Working on the fallen rocks, the same elements have slowly ground them down into particles of various sizes, producing the four clearly distinct types of foreshore that occur round our coastline.
A visitor to the seaside can recognise by a glance at the surface underfoot which of these types of coast he is on. In descending order of the size of their particles the four types are: rocky shores, shingle beaches, sandy shores, and muddy estuaries and salt-marshes.
Habitat paintings for ‘fixed’ species
Living organisms ‘recognise’ and are adapted to the different types of coastline, or ‘habitats’. If they are rooted plants or immobile animals, it is possible to predict fairly accurately where particular species will be found on the shore. The identification section which follows commences with four double-page paintings showing you where to look for particular species on the four main types of coastline.
Beginners looking at shore-life for the first time may find it easiest to start by searching for and becoming familiar with the organisms illustrated in these habitat paintings. In the paintings showing a rocky shore, a sandy shore and an estuary, additional species which may occur – sometimes at ‘zones’ or levels higher up the shore – are shown in inset panels. In the painting of a shingle beach, the panel illustrates a variety of pebbles which the beachcomber may discover.
Spotter’s charts for species that move
Many organisms, however – especially those of the open sea and the air – are not so rigidly fixed to any particular part of the shore. Though they may use one habitat rather than another in which to breed or feed, it would be misleading to regard them as being confined to that habitat.
Equipment for the keen observer
Many marine organisms lose their shape or colour if removed from the water. To appreciate their beauty to the full, and to assist identification, it is wise to use a rectangular white enamel dish in which any animals caught in a simple shrimping net can be watched and identified before they are returned to the sea. In addition, on the coast as anywhere else, the complete naturalist would also carry a lens with a magnification of x 10, a pair of lightweight binoculars and a single-lens reflex camera.
With this equipment, you should soon become familiar with most of the common plants and animals of the seashore.
THE ROCKY SHORE: LIFE ON BOULDERS AND IN POOLS
Rocky shores range widely in character, from wave-battered boulder beaches on which few species can survive to quiet protected corners with crevices and rock pools where a thousand or more species of animals and seashore plants may occur. The number of species also depends on the types of rock and the steepness of their slopes. Horizontal soft rocks such as sandstone that weather to a smooth surface provide fewer footholds or sheltered fissures than inclined hard rocks such as limestone, shales and slates.
Species are found in distinct zones up the shore according to the extent to which the various zones are exposed between tides. On exposed coasts the zones occur higher because of the effect of salt spray created by breaking waves and carried in the wind.
Parts of this ‘zonation’ can be seen re- peated in miniature at any part of the shore where vertical rocks surround a temporary pool. On the sheltered face, a broad band of brown channelled wrack at the top often gives way to a zone of spiral wrack, while the pool itself harbours a number of red seaweeds which on exposed shores are normally found much lower down.
These red seaweeds provide food and shelter for a multitude of animals. Some, such as periwinkles, live by grazing the seaweeds. Others, including barnacles and sponges, aTe suspension feeders which feed on particles floating in the sea around them, often creating a current of water to draw these particles inside their bodies. A pool left at low water will also contain predators such as sea anemones, crabs and several species of shoreline fish.
SHINGLE BEACHES: WHERE LIFE CLINGS TO THE STONES
THE SANDY SHORE: HIGH AND DRY AS THE TIDE EBBS
The millions of tiny grains of sand which make up the typical sandy shore are the product of long centuries of erosion by weathering of the sandstone or other soft rocks forming the coastline. As the tide recedes the sand dries, then becomes loose and is blown up the beach. When it meets an obstacle, natural or man-made, the sand settles and begins to form mini-dunes.
The first obstacle may be the strand-line, at the high-water mark, where shells accumulate and flowering plants grow nearest to the sea. Here nutrients from the decay of seaweeds enrich the sands, and annual plants such as saltwort and various oraches grow.
These mini-dunes are invaded by perennial plants, particularly by grasses such as lyme grass and marram. These plants form an extensive system of roots and under- ground stems which bind and consolidate the sand. Within the shelter of the grasses, other pioneer species such as sea holly and sand-dune moss become established.
On exposed coasts it is not long before these primary dunes are destroyed by winter gales and stormy seas. On more sheltered shores, however, they become stabilised, often creating a series of ridges which attract such sand-loving species as viper’s-bugloss and lady’s bedstraw. The hollows between the ridges are called ‘slacks’; they are frequently wet, supporting marshland plants and animals.
On the north-west Scottish islands, the great Atlantic rollers pound shells into fragments and these are incorporated into the lime-rich sands of the so-called machair, where wild flowers grow abundantly.
PLANTS OF THE SAND-DUNES
Sand-dune plants have to be adapted to withstand long periods of drought and frequent high winds. Some have leaves modified to reduce water loss: they may be narrow, like the leaves of lady’s bedstraw, succulent like those of saltwort, or covered in a thick layer of hairs as in viper’s- bugioss. Other sand-dune species, such as sand couch and sea holly, have long roots enabling them to tap sources of water several feet below the surface. As the early colonisers of dunes become established and the plant cover spreads, the dunes gradually become fixed and many other flowering plants and shrubs can take root on them. viscosus
ESTUARY AND MARSH: WHERE THE TIDES INVADE THE LAND
The salt-marsh that develops in sheltered bays and estuaries forms a transitional zone between land and sea. It is an area where land organisms must be adapted to frequent immersion in salt water at high tide – and where marine organisms must tolerate long periods of exposure at low tide.
Relatively few higher plants can withstand the periodic inundation and the high salt content of the sediments around their roots. Those so adapted either have mechanisms for excreting salt from their leaves, such as sea-lavender, or else are succulents, such as glasswort, which can limit the concentration of salt to a level that does not damage their tissues.
The earliest colonists of salt-marshes are often glassworts and eel grass, though in very sheltered estuaries cord grasses are more likely. Once established, their stems slow down the movement of the water; this in turn encourages the deposition of fine particles from the sea, and generally raises the level of the land. As the land rises, so it is exposed for longer and longer periods between tides, and species which are less tolerant to immersion, such as annual seablite and sea aster, are able to invade.
Higher up the shore, salt-marsh is dominated by sea-lavender and, particularly in the south, by sea-purslane. At the top of the marsh, where the land is inundated only during high spring tides, there develops a grassy sward on which sea rush and salt-marsh grass can grow. Such areas are often banked and enclosed as grazing land.
PLANTS OF THE UPPER MARSHES
Plants whose names include the prefixes ‘sea’ or ‘salt-marsh’ are highly specialised to withstand the exacting conditions of the narrow strip between sea and land. Many have thick succulent leaves which supply water for growth when it is difficult to draw moisture from the saline soils. Most such plants occur only in this habitat but some, such as common reed and scurvygrass, are more widespread.