Burrowed mud

Deep, soft mud is a surprising home for some special marine animals, including the beautiful Norway lobster, the spectacular fireworks anemone, and forests of giant seapens, resembling long white feathers growing out of the mud. On open coasts, muddy seabeds are found only in deeper water below 50m, but in the sheltered basins of sealochs, mud-dwelling creatures can be seen in much shallower water.

Why is mud important?

Deep muddy seabeds are important for Norway lobsters and their associated fisheries, but the animals that live in the mud with them are vulnerable to disturbance from these fisheries. The inner basins of sealochs, and other enclosed areas are also vulnerable to pollution and nutrification, and to changes in water movement from bridge and barrage construction. 'Mud habitats in deep water' is a priority habitat for UK Biodiversity Action Plans,  now taken forward by the Scottish Government as part of the Scottish Biodiversity Strategy  .

Where are these mud communities?

Fine mud particles only drop out of suspension and accumulate on the seabed where there is very little water movement, so this kind of seabed is mainly found in deep water. The seabed below 50m is of mud off large parts of the British coast, including the deeper areas of the North Sea and Irish Sea. However the inner basins of deep, fjordic sealochs and some Shetland voes are a version of this habitat special to Scotland. At the bottom of these basins are stable conditions similar to much deeper water on more open coasts, and animals more typical of deeper depths can live as shallow as 15m.

Fine mud particles only drop out of suspension and accumulate on the seabed where there is very little water movement, so this kind of seabed is mainly found in deep water. The seabed below 50m is of mud off large parts of the British coast, including the deeper areas of the North Sea and Irish Sea. However the inner basins of deep, fjordic sealochs and some Shetland voes are a version of this habitat special to Scotland. At the bottom of these basins are stable conditions similar to much deeper water on more open coasts, and animals more typical of deeper depths can live as shallow as 15m.

Mud-lovers

Sea pens, relatives of sea anemones and corals, are perhaps the most characteristic and conspicuous animals in the mud. Anchored by a bulbous base, their many small polyps trap plankton and other food particles from the surrounding seawater. The slender sea pen Virgularia mirabilis is the commonest, while the beautiful phosphorescent sea pen Pennatula phosphorea can glow when disturbed. The tall sea pen Funiculina quadrangularis is common in very deep water, but occurs as shallow as 25m in some fjordic sealochs, where it can form eerie white 'forests'. It is sometimes host to the curious deepwater brittlestar Asteronyx loveni that hangs on to it with one or two of its five long, coiled arms, using the others to catch food. Another speciality of sealoch mud is the big fireworks anemone Pachycerianthus multiplicatus, which has a stunning crown of long, pale tentacles up to 30cm across, and can retreat into a mucus tube extending up to 1m into the mud.

Burrows and mounds between the sea pens are clues that other creatures live within. Beautiful Norway lobsters Nephrops norvegicus (also known as langoustines, Dublin Bay prawns and scampi prawns), bulldoze simple 'U"-shaped burrows where they sit during the day, coming out at night to forage for food. Sometimes a small fish, Fries' goby Leseurigobius friesii shares the burrow. Other crustaceans, including the mud shrimps Callianassa subterranea and Calocaris macandreae, and the angular crab Goneplax rhomboides, make more complex burrows, with interconnecting tunnels and side chambers.

Burrowing brittlestars (Amphiura spp) may be abundant in places, with just the ends of their long, slender arms showing above the mud. Strange echiuran worms form large mounds, making characteristic scoop marks on the mud surface. There are even single-celled organisms called 'giant naked foraminiferans' lurking in the mud, looking like stringy cottage cheese! The activities of all these animals help to aerate the mud, which would otherwise become anoxic (lacking in oxygen) just below the surface. On mud at 65m in Loch Goil, there is an unusual community with abundant seasquirts, including the rare Styela gelatinosa, along with terebellid worms and the seven-rayed scallop Pseudamussium septemradiatum - an odd assemblage of animals which may be a relict from the last ice age.