Seabed

Habitat Features of Conservation Importance (FOCI)

22 habitat FOCI were identified by JNCC and Natural England from the Initial OSPAR List of Threatened and/or Declining Species and Habitats; the UK List of Priority Species and Habitats (UK BAP), and Schedule 5 of the Wildlife and Countryside Act (1981). These are to be protected in the regional MCZ project areas where they occur. From the available distribution maps, 11 of the 22 occur in the Balanced Seas area. Additional data may reveal the presence of listed FOCI habitats in the Balanced Seas area (e.g. Oyster beds).

Blue Mussel Beds (including intertidal beds on mixed and sandy sediments)

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Blue mussels can form extensive beds, with living and dead mussels, sand and mud all bound together by the mussels’ sticky ‘beards’ of byssus threads. Mussel beds provide an important food source for wintering waders. Have a particularly important role where they occur on soft seabeds, as they provide a hard surface in otherwise muddy or sandy areas. This attracts and supports a diverse range of marine life. Vulnerable to removal or damage by fisheries or anchoring, or effects of developments, dredging and pollution. 

Click here for more information on blue mussel beds
 
 

Estuarine rocky habitats

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Estuaries are usually soft, muddy places, so rock and stable boulders in estuaries are rare. They form a small proportion of estuarine seascapes but contribute a lot to the richness of estuarine life and provide part of the nursery habitat of estuaries.  

Threats to estuarine rocky habitats include mobile fishing gear, dredging, coastal protection, pollution and, potentially, climate change and sea level rise.
 
Click here for more information on estuarine rocky habitats
 

Intertidal underboulder communities

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To marine life, the damp and shaded area underneath boulders is a different environment from the rest of the shore.   A ‘boulder’ can be anything larger than 25cm across. Important communities of plants and animals begin to develop where there is a sufficient gap on the underside of the boulders. Such communities can occur anywhere from the mid-shore down to extreme low water, but the richest examples are often found where there is running seawater (for instance, from pools or lagoons emptying after the tide has fallen). Sea mats, sponges, sea squirts, barnacles, coat-of-mail shells, tube worms and tufts of pink coralline seaweed encrust the undersurfaces. Sea slugs, such as the sea-lemon, feed on encrusting sponges and the European cowrie eats sea squirts. Brittlestars, porcelain crabs (which are actually lobsters) and squat lobsters also cling to the undersides of boulders. The undersurfaces are an important refuge for the eggs of fish, dog whelks and sea slugs. Crabs and fish hide amongst the boulders, and they may be a particularly important shelter for young edible lobsters.

Threats to these habitats include boulder turning when hunting for soft ‘peeler’ crabs and winkles, and by people exploring the shore – the failure to return overturned rocks to their original position can be devastating for the community living beneath it. Important underboulder communities have been found along the coast of Northumberland, near Plymouth, in the Isles of Scilly, the Menai Strait and at the entrances to sea lochs.
 
Click here for more information on intertidal underboulder communities
 
 

Littoral Chalk Communities

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Chalk is a soft, pure limestone and is easily eroded by seawater. These have particular communities of plants and animals associated with them at each level of the intertidal area.

Human impacts include coastal protection works. This has a greater effect on the chalk at higher levels on the shore. Large port and harbour developments can have major impacts on the lower shore and shallow waters. Also vulnerable to pollution and oil spills, and habitat is lost through human disturbance - trampling, stone-turning, small-scale fisheries. Native species have been displaced by the invasion of non-native plants. Chalk communities are scarce, and so any impacts have a significant effect.

Click here for more information on littoral chalk communities

 

Mud habitats in deep water

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Offshore deep-sea muds are fairly stable environments as they are not affected by waves. The animal communities vary according to the levels of silt, clay, sand and nutrients found in the mud. Species such as bristleworms, brittlestars, cockles and Norway lobster can be present in large numbers. 

Disturbance from trawling, anchoring, offshore oil and gas and major constriction on land can threaten these communities.   
 
Click here for more information on mud habitats in deep water
 

Peat and clay exposures

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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.

These unique and fragile habitats are irreplaceable, as they were formed millions of years ago from ancient lakebeds and forested peatland. They are threatened by coastal infrastructure development, cable laying, dredging and other activities that disturb the seabed, mussel fisheries and the collection of the piddocks for bait.
 
Click here for more information on peat and clay exposures
 

Rossworm (Sabellaria spinulosa) reefs

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Ross worms build tubes from sand and shell fragments. The tubes of large numbers of the worms can form reefs, which at their largest can be about half a metre in height and cover an area of several hectares. Reefs provide habitat for a wide range of other seabed-dwelling animals. Where they occur on the soft seabed, they are of particular significance for nature conservation.   By providing a complex seascape with hard surfaces and nooks and crannies in an otherwise flat, featureless seabed, they provide a home for animals which would not normally be found there.

Most vulnerable to physical disturbance from fishing activities such as dredging for oysters and mussels, trawling for shrimp or finfish, net fishing and potting. While the reefs appear to recover well from minor damage, serious impacts from mobile fishing gear break the reefs down into small pieces. Aggregate dredging often takes place in areas of mixed sediment where Rossworm reefs may occur, but the effects of this on the reefs are being investigated
 
Click here for more information on Rossworm reefs
 

Seagrass beds

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Seagrass has dark green, long, narrow, ribbon-shaped leaves and grows in sheltered waters such as inlets, bays, estuaries and saltwater lagoons, forming dense underwater ‘lawns’. It grows mainly on sand, but also fine gravel, from intertidal typically down to a depth of 4m. They are an important food source and provide nutrients to support animal communities on the seabed. Their roots catch and trap sediments, reducing coastal erosion. Submerged seagrass beds are also used as a nursery area, protecting young fish and shellfish and provide a habitat for many other animals, such as pipefish and seahorses.

Threatened by pollution, physical disturbance and by increased amounts of sediment in the water, which block sunlight and prevent seagrass growth.   Introduced species and disease can also damage seagrass beds.  Areas affected by disturbance are slow to recover.
 
Click here for more information on seagrass beds
 

Subtidal chalk

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Underwater habitats of chalk are rare in Europe, with those occurring on the southern and eastern coasts of England accounting for the greatest proportion. In shallow water (<5m deep) fauna is dominated by burrowing piddocks, sponges, crabs and worms. In deeper water, reefs and sea caves may form in the chalk, in which rare species of sponge have been found.  

Human impacts on these habitats include coastal defence and other works, with major ports and harbour developments having the biggest impact. Small-scale fisheries can also cause damage to soft chalk reefs. Pollution has affected the seaweeds occurring on chalk seabeds.  
 
Click here for more information on subtidal chalk
 

Subtidal sands and gravels

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Sand and gravel seabeds occur in a range of environmental conditions, from wave-sheltered, enclosed bays and estuaries to highly exposed open coasts. The communities of animals that live in this habitat are determined by the environmental conditions. There tend to be fewer animals where waves and tides are strong, and the communities there will be characterised by rapid burrowers. In quieter and deeper areas, sand and gravel seascapes can support some of the richest marine life communities. Offshore gravel and sand habitats support internationally important commercial fisheries, such as those for scallops and flatfish.   They are also are important nursery grounds for the young of commercial fish species such as flatfish, bass, skates, and rays as well as sharks.

Trawling and aggregate dredging present the greatest threats to sand and gravel communities, which can also be at risk from pollution, coastal development and oil exploration.
 
Click here for more information on subtidal sands and gravels
 

Tide-swept channels

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Tide-swept channels occur where the constricted coastline acts as a funnel. The plentiful supply of food brought in on each tide supports rich and varied communities of marine life.

Tide-swept rocky shores that emerge between the tides support seaweeds such as kelp and sea oak, which grow to great lengths in the currents. Where the seabed is of coarse gravel, it is constantly moving and difficult to inhabit. Even here there are animals, such as sea cucumbers, worms and burrowing anemones.
 
Construction of bridges and causeways can disrupt the water flow damaging these communities. Edible species such as mussels may occur in large numbers, making them attractive to fisheries. Crabs, on the other hand, may be safer in tide-swept channels as the conditions make pot or creel fishing difficult. 
 
Click here for more information on tide swept channels
 

Broad scale habitats

The information about how to select which areas of habitats to protect is based on classification system which is used across Europe. It is used to describe all types of habitats, from natural to artificial, and from terrestrial to freshwater and marine.  Habitats for the marine environment are described on three factors:

·         geology (rock, sand, or sediment),
·         location on the shelf (from the high tide to the edge of the continental shelf)
·         amount of energy (wave and tidal action or exposure to weather) they receive.
 
There are a total of 23 of these habitats in the English inshore and offshore seas. Eight of these are found within the subtidal areas of the Balanced Seas project area, and these are described below. 
 

Information about the other habitats present around England can be accessed here 

High energy circalittoral rock

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Deeper water rock, exposed to very strong waves and currents
 
As the water depth increases, the lack of sunlight prevents seaweeds from growing, and the marine environment becomes dominated by animal communities. Unlike shoreline and shallow water areas, this zone is rarely characterised by a single species but is a mosaic of different marine creatures. The types of animals that live in this zone vary enormously and are affected mainly by wave action, the strength of the tidal stream, the levels of freshwater arriving from rivers, the clarity of the water, the degree of scouring as sand is swept past, and the shape of underwater rock formations.
 
Some underwater seascapes of bedrock and boulders are swept by strong waves or swift currents. The animals that thrive here include colourful sponges clinging to the rock and a dense 'carpet' of sea firs. A large, volcano-shaped barnacle lives here and the soft coral, dead men’s fingers is often present on rocky outcrops. Found on exposed rocky headlands and coastlines, where they are exposed to the prevailing south-westerly wind. Balanced Seas has a considerable amount of bedrock habitat south of the Isle of Wight and some smaller areas just off the coast at Dover.
 
 

Moderate energy circalittoral rock

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Deeper water rock, with some shelter from waves and currents
 
Seaweeds tend to dominate shallow coastal areas, but as the water depth increases and there is insufficient sunlight for seaweed growth, animal communities are able to prevail.
 
The types of animals that live in this zone vary enormously. The strength of the waves and the speed of the tidal stream are two important factors that affect where the different animals set up home. Where bedrock and boulder seascapes are affected by moderate wave action and fairly strong tidal streams, the animal communities can include cup coral, sea-fans, and anemones, or they may be dominated by sponges. Mobile animals in this environment include starfish, brittlestars, and sea urchins. It is also possible to find rock borers and piddocks, which are both types of bivalves (with paired, hinged shells) that burrow into soft rocks such as limestone. Mussel beds and worm reefs can also occur in the moderate wave and tide environment of these rocky areas.
 
Found on exposed rocky headlands and coastlines. Considerable distribution through the Balanced Seas area off the south coast.
 
 

Subtidal coarse sediment

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Undersea beds of coarse sand, gravel and shingle
 
Close to the shore, coarse sand, gravel and shingle seabeds are found on the open coast or in tide-swept marine inlets. These areas are disturbed by waves and tides, which prevent finer sands and mud from settling. Most of the animals that live here are found buried in the seabed – the safest place to be. Even as the water becomes deeper, most of the life remains beneath the surface, and the animals found there include bristleworms, sand mason worms, small shrimp-like animals, burrowing anemones, carpet shell clams and venus cockles. Small varieties of calcareous algae may also live on fine gravels.
 
In much deeper water, coarse sand and gravel or shell fragments may cover large areas of the continental shelf. At present, little is known about its ecology, due to the technical difficulties of exploring deeper water. Widespread around the British Isles and mainland Europe. Distributed throughout the Balanced Seas area, inshore and offshore.
 
 

Subtidal mud

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Undersea beds of mud
 
Muds and sandy muds occurring in areas too deep to be exposed to the tide are mainly found in extremely sheltered areas with very weak tidal currents, such as sea lochs and some estuaries and harbours.
 
High numbers of worms, cockles and other bivalve shells, urchins and sea cucumbers live in muddy sea beds and sea pens, burrowing anemones and brittlestars can also be found there.  The size of the animals depends on the type of mud they are found on. On the softest mud, there are fewer animals, but they grow relatively fast, and reach a large maximum size. On sandier mud, species such as the Norway lobsters are more densely distributed but grow more slowly, and are smaller. In some muddy areas, perhaps as a result of pollution or of limited exchange of water with the open sea, not enough oxygen is transferred into the mud. As a result, the seabed turns black just below the surface. Most creatures find it impossible to survive in these conditions, and there if often little living there except bacteria. Widespread in sheltered seas around the British Isles and mainland Europe. Balanced Seas contains very little of this habitat, which is confined to tiny patches in the Thames estuaries, the Solent and off Dungeness.
 

High energy infralittoral rock

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Shallow water rock, below the tides, exposed to very strong waves and currents

On exposed rocky coastlines that are subject to strong waves or swift tidal currents, the shallow underwater environment (which may be exposed to the air on the lowest of tides) tends to be dominated by the large kelps and some smaller red seaweeds. Where the water is very clear, this zone can be wide, reaching as far as an exceptional 45m deep. Rock surfaces are dominated by animal communities of sponges, sea squirts, sea mats, mussels and barnacles. Kelp forests are also important for young fish.
 
This habitat is found on rocky coastlines, exposed to the full force of the prevailing south-westerly wind. Exposed rock below low water mark is found throughout Britain where they are exposed to the prevailing south-westerly wind. In mainland Europe, they are associated with south and west facing rocky headlands and coastlines. In Balanced Seas, found along the south coast incorporating much of the chalk habitats in this region.
 
 

Moderate energy infralittoral rock

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Shallow water rock, below the tides, with some shelter from waves and currents
 
Where rocky cliffs and boulder seascapes are found in areas of moderate wave action and fairly benign tidal currents, the marine life is dominated by seaweeds, which will extend as far below the surface as the penetration of sunlight allows. In shallow underwater areas, the top of which may be exposed on the lowest tides, there is often a narrow band of oarweed above a forest of tangle kelp. These large seaweeds provide a home for all sorts of small marine creatures, which shelter and feed amongst the leaf-like fronds and within the holdfast by which the kelp attaches to the seabed. Amongst and below the kelp are different kinds of red seaweed, including more of the delicate thread-like seaweeds that cannot colonise areas with stronger waves or tides. The red seaweeds are grazed by animals including top shells, sea urchins and sea slugs.
 
Exposed rocky and boulder shores are found throughout Britain where they are exposed to the prevailing south-westerly wind. In mainland Europe, they are associated with south and west facing headlands and rocky coastlines. Balanced Seas has a small amount of this habitat along the inshore area of the south coast.
 
 

Subtidal mixed sediments

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Undersea beds of stones, gravels, sands and muds
 
As the name suggests, mixed seabeds can have a range of different types of sediment from muddy, gravely sands to mosaics of cobbles and pebbles in or on a sand, gravel or mud seabed. Mixed areas also include seabeds where waves or ribbons of sand form on the surface of a gravel bed.
 
Because mixed seabeds are so varied, they may support a wide range of animals, both on and in the sediment. Animals found here include worms, bivalves (with their paired, hinged shells), starfish and urchins, anemones, sea firs and sea mats.  
 
Widespread around the British Isles and in Europe. A moderate amount found in the Thames Estuary area of the Balanced Seas region, with additional tiny scattered patches off the south coast.
 
 

Subtidal sand

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Undersea beds of sand
 
Sandy seabeds usually occur on open coasts, and close inshore they are often disturbed by waves and tides.   Sand seascapes may appear like deserts, but close inspection can reveal flat fish and sand eels camouflaged on the surface of the sand, and worms and bivalves (with their paired, hinged shells) living within it.
 
Found in estuaries and marine inlets where the coast is more sheltered with smaller waves and the tidal currents are reduced, more silt will combine with the sand. Different groups of animals are found here, with the exact types depending on the sand/mud mix. Heart urchins, razor shells and sea cucumbers can all be found in muddy sands. 
 
Widespread around the British Isles and mainland Europe. Found throughout the Balanced Seas area, predominantly in the Thames Estuary.