Purple sea fan

Appearance

"Gorgonia ventalina" is a fan-shaped colonial coral with several main branches and a latticework of linking smaller branches. The skeleton is composed of calcite and gorgonion, a collagen-like compound. The calyces in which the polyps are embedded are in two rows along the branches. Many of the smaller branches are compressed in the plane of the fan, a fact that distinguishes this species from the Venus sea fan. It often has small accessory fans growing out sideways from the main fan. It grows to 1.5 metres tall and is variable in colour, being whitish, yellow or pale purple. The main branches are often purple and the fan is orientated at right angles to the current.

Distribution

"Gorgonia ventalina" is found in the western Atlantic and Caribbean Sea with a range extending from Bermuda and Florida and the Gulf of Mexico to Curaçao. It grows near the shore in shallow water in areas with strong wave action and on deeper outer reefs with strong currents down to a depth of about 15 metres.

Habitat

"Gorgonia ventalina" is found in the western Atlantic and Caribbean Sea with a range extending from Bermuda and Florida and the Gulf of Mexico to Curaçao. It grows near the shore in shallow water in areas with strong wave action and on deeper outer reefs with strong currents down to a depth of about 15 metres."Gorgonia ventalina" is a filter feeder. Each polyp extends its eight tentacles to catch plankton drifting past on the current. Its tissues contain a symbiotic dinoflagellate "Symbiodinium spp." which is photosynthetic and uses sunlight to create organic carbon compounds which are then available to the host coral.

The skeleton of "Gorgonia ventalina" contains hard structures known as sclerites which are unpalatable to predators. It also contains certain secondary metabolites in its tissues which are distasteful. The nudibranch "Tritonia hamnerorum " seems undeterred by these defences and is often found associated with the coral. While feeding on the coral it concentrates the metabolites in its tissues which renders it unpleasant to potential predators.

This coral is sometimes attacked by the fungus "Aspergillus sydowii" which causes the disease aspergillosis. This results in damaged patches, galls, purpling of the tissues and even coral death. There have been several epizootics in the Caribbean and corals growing in stressful conditions such as in low salinity water in estuaries seem specially susceptible.