88.
THE SANDY SEA BED

Away from the shoreline and its fringing kelp reefs, the sea bed changes from rock to sand and mud. The sandy sea bed stretches away from the coast to cover the Moray Firth bay and out to the North Sea.

Shifting Sand
Although the effects of the waves are felt less in the deeper water, the fine sand particles that settle out are easily moved by any water motion. This means that it is unsuitable for seaweeds to take hold and grow, so the primary producers (photosynthesising plants) of this ecosystem are the tiny algae of the surface waters, phytoplankton.

Eating Dirt
In the absence of large plants and much primary production, detritus is a very important food source for the inhabitants of the sandy sea floor. Organic particles and debris are brought in by currents from estuaries and the more productive rocky shores. The animals that live on detritus, for example, bivalve molluscs (7) such as cockles and razor shells, mostly burrow in the soft sediment and filter the water for suspended particles. When buried, bivalves protrude a pair of siphons from their burrows to draw in water containing supplies of food.

Polychaete worms(6) also make a living by eating detritus. Lugworms live in burrows. Fan worms, like the peacock worm and the sand mason worm, build tubes above the sea floor from sediment particles and hold delicate tentacles up in the water column. Sea pens (5), relatives of corals and anemones, are also common filter feeders on the sea floor.

Hunters and scavengers
The abundance of detritus feeders on the sea floor attracts other creatures which feed on them. Crustaceans (8), such as hermit crabs, wander about the sediment surface scavenging their meals, while the Norway lobsters (31), also known as scampi, live in large, shallow burrows which they excavate in the mud and can grow up to 15 centimetres long. A large area of the southern Moray Firth, centred on Buckie, is fished for Norway lobsters, and this is now the most valuable fishery in the Moray Firth. The animals are caught either in baited creels or by trawling, the former method being much less damaging to other marine life on the seabed.

Many fish exploit the food source provided by the worms, crustaceans and molluscs. Commercially important species such as cod(30), haddock(30) and plaice(30) all feed on or around the sea bed. Cod use their sensitive chin barbel to find food in the murky waters. Flat fish and rays lay camouflaged against the sandy floor, ready to ambush any passing prey. Small sharks - dogfish and starry smooth hounds - also patrol the sea bed for food. Sand eels are small arrow-like fish which bury themselves at night, or when predators approach, and feed on the abundant crustaceans and worms. They themselves provide food for other fish, marine mammals and birds.

Sources:
Lets Look at the Moray Firth(86)
Macduff Marine Aquarium - Teacher's Guide(86)