Northern sea fan, Swiftia pallida

It might seem surprising to find sea fans in cold Scottish waters, and they are certainly more typical creatures of the tropics, but the northern seafan (Swiftia pallida) thrives off our west coast. Although it looks plant-like, the northern sea fan is a colonial animal, related to soft corals. It grows up to 20 cm tall

Why is it important?

Nearly all the British records of the northern sea fan are from western Scotland, so we have a particular responsibility for this 'national' treasure. Both the northern sea fan and the rare sea fan anemone which lives on it, are priority species for UK Biodiversity Action Plans   and have been taken forward by the Scottish Government as part of the  Scottish Biodiversity Strategy  .

Where does it live?

The northern sea fan has been found from Oban northwards to the east coast of Lewis. It also occurs in the Kenmare River in west Ireland, the only place where its distribution overlaps with that of the pink sea fan (Eunicella verrucosa), our only other British sea fan. The northern sea fan also occurs on the southwest coast of Scandinavia, and in much deeper water further south, in the Bay of Biscay and the Mediterranean (down to 600m)..

The northern sea fan usually grows in relatively sheltered, deeper water (below 20 m), on flat or sloping bedrock with some current but little wave action. These conditions are found off the east coasts of the southern Western Isles, at the entrances to some mainland sea lochs, and on deeper submerged reefs in the Minches. It often grows with cup sponges, the hard branched orange bryozoan (Porella compressa), and the deepwater  northern feather star  (Leptometra celtica), species that seem to thrive in similar conditions, and together they form a characteristic suite of animals.

How does it live?

The sea fan's horny skeleton is covered with soft tissue, from which many small polyps with eight branched tentacles arise. The northern sea fan feeds by catching small animals in the plankton, and other food particles sinking from above, using sticky and poisonous nematocysts on its polyps. Many sea fans, as their name suggests, are fan-shaped, and often grow orientated across the water current to increase their chances of catching food. The northern sea fan has a rather straggly appearance, with loose branches not confined to one plane, perhaps (at least in deep water) because more of its food falls from above. Otherwise, little is known of the biology of this sea fan.

The rare sea fan anemone (Amphianthus dohrnii), which grows almost exclusively on sea fans (rarely on sea firs), has been seen occasionally on northern sea fans in the Forth of Lorn. Apart from taking up space, and perhaps competing for food, this little anemone appears to do no harm to its host, using it simply as a perch to raise it above the seabed. The anemone, which measures only about 1.5 cm across, reproduces by splitting at its base, which often results in several genetically identical anemones on the same sea fan. The sea fan anemone has apparently declined throughout its range in recent years