Diving with Subergorgiidae Giant Fans

Lanta Marine Life | Subergorgiidae

Giant Sea fans are a common sight at many of the Koh Lanta dive sites, including the Bida islands, Phi Phi, Koh Haa, and Koh Rok.

The six species in this family have strengthened their inner skeletons with gorgonin to such an extent that they are far less brittle than other related soft corals.

There are three genera in this family. The genus rosgorgia contains a single species which is confined to Antarctic waters, and the remaining two are tropical. These two genera can be easily distinguished by their growth patterns, and neither have symbiotic algae.

The Giant Sea fan genus Subergorgia contains three species which are tree-like with stems and side branches. All branches have a narrow but deep groove running along their entire length.

The genus Anella contains two species which are fan-like with branches arranged in a net-like manner with a very small mesh. Due to the much-strengthened inner skeleton, these corals can grow several meters in height and diameter, with the central branches being much thicker than the others.

The colour of the branches varies from dark red (rare) to yellowish-orange or cream-coloured.

1 species found on this page:

Giant Sea Fan (Annella mollis)

Giant Sea Fan

(Annella mollis)

This is a slow-growing fan coral species, however colonies of this species can grow to gigantic sizes, reaching several meters high and several meters wide. This is the largest species of fan coral found on Indo-Pacific coral reefs, feeding on microplankton, which they sift out the water using the polyps (filter feeding).

Annella mollis @ Koh Bida

Annella mollis has a very tough, narrow-meshed skeleton, consisting of fused sclerites and gorgonin which is extraordinarily flexible and perfectly suited to strong currents. These sea fan colonies vary in colour from cream-coloured to pink and orange.

This species never occurs in shallow water. The colonies live between 10 m and 50 m, and preferably settle on steep drop-offs and on deeper reef flats where strong currents prevail.

Giant Sea Fans @ Shark Point

A large and diverse population of other remarkable animals and plants often live on the gigantic fans. Algae, bivalves, and bryozoans are most common, and during the night a multitude of brittle stars visit these fans for an exposed position in order to catch plankton.