These small, blue mussels (Mytilus edulis) are a common sight on UK coasts. They can form extensive beds, with living and dead mussels, sand and mud all bound together by the mussels’ sticky ‘beards’ of byssus threads. Blue mussel beds occur mostly on the lower shore between the tides or permanently submerged in shallow water.
Most people think that coral reefs are only found in the tropics and are surprised that we have them in our cold seas. Even experts are discovering that the world's oceans contain far more cold-water coral reefs than previously thought.
When we think of corals, we think of shallow, warm tropical seas, not the cold, dark oceans around Britain. However, in varying depths of water – from 30m to several thousand metres deep on underwater mountains – there are beautiful coral gardens. They are made up of dense aggregations of colonies of one or more coral species. In some locations, there may be up to 700 colonies in an area of one hundred square metres.
In some deep-sea areas, sponges may represent as much as 90% of the weight of living material within the community (excluding fish). These aggregations are mainly made up of two types of sponge: the glass sponge and the giant sponge. They occur offshore in water depths of between 250m and 1300m, where currents are moderate and temperatures do not exceed 10°C. They are found on seabed types from silt and mud to boulders, and can occur in the rocky ridges formed as icebergs ploughed through the seabed at the end of the last ice age.
Estuaries are usually soft, muddy places, so rock and stable boulders in estuaries are rare, and occur mostly in drowned river valleys and fjords. They form a small proportion of estuarine seascapes but are important because they contribute a lot to the richness of life within estuaries. The rich and sheltered waters of estuaries provide nursery grounds for fish, and the rocky areas are an important part of these.
The file shell is a very distinctive bivalve. The two halves of its shell do not close completely, and a thick fringe of bright orange or red tentacles extends between them.
Large colonies of sponges, anemones and sea-fans growing on rocks in shallow water.
Honeycomb worms (Sabellaria alveolata) build tubes from sand and shell fragments.
Horse mussels (Modiolus modiolus) are common on UK coasts, and are important to conservation where they form extensive beds in otherwise featureless sandy and muddy seascapes.
The marine life living under boulders on the seashore.
Special communities of animals and seaweeds that live on chalk seashores.
Maerl is a collective term for several species of red seaweed, with hard, chalky skeletons. It is rock hard and, unlike other seaweeds, it grows as unattached rounded nodules or short, branched shapes on the seabed. Like all seaweeds, maerl needs sunlight to grow, and it only occurs to a depth of about 20m.
Offshore deep-sea muds are fairly stable environments. At depth they are not affected by waves. They occur at depths of 200-500m, in areas where the currents are slow.
In shallow water (usually less than about 10m deep) on fine, muddy sand, native oysters (Ostrea edulis) can be found in large numbers.
Seabeds formed of exposed peat or clay, or in some cases both, are uncommon. Where they do occur, they have been found between the tides as well as fully underwater. They can be buried by sand or other sediments and then exposed again on a regular basis.
Ross worms (Sabellaria spinulosa) build tubes from sand and shell fragments. The worms are usually found individually, but in some shallow water areas they are found in colonies
Areas of stable muddy seabed, where animals burrow below and sea pens protrude from the surface.
Seagrasses (also known, for their long thin leaves, as eel grass) are grass-like flowering plants with dark green, long, narrow, ribbon-shaped leaves. They are one of the very few groups of flowering plants that live in the sea. Two species of eel grass are found in England and all are considered to be scarce. They grow in sheltered waters such as inlets, bays, estuaries and saltwater lagoons.
Muddy gravels occur mainly in estuaries, drowned river valleys and sea lochs, in areas protected from wave action and strong tidal streams. They can be found both on the shore and in the shallows, and are probably an extension of the much more common offshore sands and gravels.
The chalk coasts of the south-east and Yorkshire are very different from the harder rock coastlines of western and northern Britain. The chalk seabed can continue below the low water mark, and the largest areas of these underwater chalk seascapes are most found in Kent and Sussex.
Sand and gravel seabeds are widespread. Those found to the west of the UK include a high proportion of shell fragments, whereas those from the North Sea are mainly formed from rock. They occur in a range of environmental conditions, from wave-sheltered, enclosed bays and estuaries to highly exposed open coasts. The mix of sand or gravel, and any sand waves or ripples present on the surface of the seabed, depend on factors such as the strength of the waves and tides.
Tide-swept channels occur where the constricted coastline acts as a funnel. They are found at the entrances to fjords, lochs and lagoons, between individual islands, and between islands and the mainland. The plentiful supply of food brought in on each tide supports rich and varied communities of marine life.