Sea Lochs

Scotlands Living Landscapes

• Introduction
• How were sea lochs formed
• What’s special about sea lochs?
• Seashore life
• Rocky shores
• Tidal rapids
• Maerl beds
• Brittlestar beds
• Living reefs
• Seabed life
• Floating life
• Mammals
• Birds
• Sea lochs and people
• Fishing
• Seaweed harvesting
• Fish farming
• Tourism
• Ports and harbours
• The importance of sea lochs
• Threats to sea lochs

Seabed life

Very sheltered, deep (more than 30 metres) bedrock is a special feature of many sea lochs which supports marine life found nowhere else in Britain. At this depth, daylight is either very much reduced or complete darkness prevails, which means that no plants can survive, so animals dominate the communities. Steeper slopes are often covered with sea squirts and small white anemones, neatly spaced just out of reach of their neighbour’s stinging tentacles. Bunches of long, muddy tubes made by peacock fan worms stand out from the rock, crowned with delicately beautiful orange and blue feeding fans. Upward facing rock is often covered with a thick layer of silt. Underneath the silt small limpets and chitons are found, while sea firs and large sea squirts hold their bodies above the layer of silt and small brittlestars often crawl over the silty surface.

In deeper water (more than 50 metres), small, two-shelled animals stud the rocks. These are known as lamp shells because of their resemblance to old oil lamps. Having survived almost unchanged for the last 400 million years, these lamp shells are truly ‘living fossils’.

Near the entrances to sea lochs a variety of erect sponges of different shapes and colours grow on deep sheltered bedrock together with the white, slender coral known as the Northern sea fan. Rock surfaces may also be studded with the small Devonshire cup coral, a true, solitary coral with a hard, ribbed skeleton.

The holes between boulders and cobbles provide ideal homes for mobile animals such as squat lobsters, crabs and fish. The shy, leopard-spot goby looks out for predators while other territorial fish such as the goldsinny, ballan and cuckoo wrasse also retreat to boulder holes. Larger holes may occasionally be occupied by a lobster or conger eel, both active mainly at night. Between and underneath boulders, brittlestars, sea squirts and worms are just a few of the animals found.

Seabeds in the shallower parts of sea lochs are often a mixture of mud, sand, gravel and shells. These mixed sediments can be rich in marine life, both on the surface and buried. In the shallowest parts, seaweeds grow on any small pebble or shell, competing with animals such as barnacles, sea firs and sea squirts for space. Hard surfaces on which to grow are at such a premium that the shells of live scallops may be overgrown with seaweeds and other marine growths. Small fish such as sand gobies, dragonets and young flatfish adopt camouflage colours against the sand, lying in wait for the small crustaceans on which they feed while avoiding being eaten themselves.

Many animals lie buried in the sand stretching out tentacles or arms to feed, but withdrawing into the safety of the sediment if disturbed. Burrowing sea anemones, sea pens, worms, sea cucumbers and brittlestars all live like this while some bivalve molluscs are even less conspicuous, showing just a pair of siphons as holes at the surface. Some seldom seen animals move along below the sediment surface looking for buried prey, like the sea mouse (a kind of worm), the elusive pelican’s foot shell and the thin leaf-like goosefoot starfish.

In the most sheltered and deepest parts of sea lochs much of the seabed is of soft, deep mud and home to some spectacular and specialised animals found in no other habitat. Seapens are long, white, feather-like animals related to corals, which stick up from the mud and can form dense beds. All three British species grow in sea lochs but most characteristic of deeper water is Funiculina quadrangularis which can grow up to a metre tall. In some places it plays host to a brittlestar, Asteronyx loveni, which clings on to the upper regions of the seapen using two of its five arms, while the others are left hanging out in the water to capture food particles. The bright orange Norway lobsters excavate wide, U-shaped burrows and sit in the entrance, sometimes accompanied by a small goby which shares the burrow. Perhaps the most spectacular of all mud-living creatures is the fireworks sea anemone, Pachycehanthus multiplicatus, which has a crown of kinked, white tentacles up to 30 centimetre across.