Papa Stour marine cSAC Subtidal areas

 
The distinctive casts shown in the photograph left provide evidence that lugworms are about. These large worms live in j-shaped tubes beneath the surface, forming casts in the fine muddy sands as a result of their feeding habits. Within Papa Stour cSAC this habitat is found in sheltered areas, such as Housa Voe and Hamna Voe on the east and south coasts of the island respectively. A green cord-like seaweed known as mermaid's tresses also grows here.

Few plants and animals are visible within this habitat.

Along the site's eastern boundary is the largest area of coarse sand and shell gravel. Empty razor shells, swimming crabs and common starfish live here, and the rare sub-artic starfish Hippasteria phrygiana has been found.

Brittlestar beds occur in the deeper waters of the site, on sand-covered low-lying bedrock and cobbles. There are two species, the black and the common brittlestars, which can occur in very dense beds of up to 100 per square metre. Other animals may live within these areas including common starfish, the soft coral dead man's fingers and horn wrack.

 
The soft coral Dead man's fingers is a characteristic species of many of the reefs in the deep waters below the kelp forests and parks of Papa Stour cSAC. A range of plants and animals including keel worms, dahlia anemones, sea urchins and red and coralline algal crusts may be found, with hydroids forming dense turfs. The latter are also known as sea firs and are related to both anemones and corals.

Sugar kelp covers much of the shallow seabed within Papa Stour cSAC. Filamentous brown algae, foliose green algae and Mermaid's Tresses grow on the mixture of pebbles and gravel.

This is not a common habitat within Papa Stour cSAC and is found mainly in Papa Sound. It consists of mixed kelps on bedrock and cobbles subject to scour as a result of strong tidal flows lifting sand from the surrounding sea bed.

This biotope covers most of the area between Papa Stour and the Mainland, known as Papa Sound. It also extends in a narrow band around much of the island. Plant life is dominated by kelp sporelings (young plants) of various species, with Sugar kelp and foliose red algae also attached to the rocks. The presence of large areas of sand and fast tidal flows result in this community being subject to fairly heavy scour, as the water transports sediments across the Sound.

Oarweed parks consist of kelp attached to bedrock, boulders and cobbles. The species here are similar to those found in Oarweed forests (see 10.), however both flora and fauna are much more sparse.

These forests cover much of the shallow subtidal areas within Papa Stour cSAC both around the island and along the coast of the Mainland. They are made up of dense patches of Oarweed, Laminaria hyperborea, attached to the bedrock and interspersed with patches of coarse sand. Red algae is present on the kelp stipes and the underlying bedrock. Other plants include encrusting corallines and red algal crusts. Keel worms can be abundant and sea urchins may be important grazers in some areas.