Alcyoniidae is a family of leathery corals that occur globally in temperate and tropical seas. These reef dwellers are often found in wave-exposed areas of reef crests, less turbid waters in lagoons, on steep slopes, under overhangs, and at depths of 100 feet and deeper.
A colony of leathery coral is stiff, hard, and inflexible. It is composed of tiny polyps projecting from a shared leathery tissue. There are two kinds of polyps seen in Alcyoniidae corals: autozooids have long trunks and eight tiny branched tentacles and project from the shared leathery tissue; siphonozooids remain below the surface and pump water for the colony. The siphonozooids appear as tiny hollows among the taller autozooids. Different genera have different proportions of these polyps. Autozooids only emerge when the colony is fully submerged.
The polyps also host an algae called zooxanthallae. This algae undergoes photosynthesis and produces sugars from sunlight. The food produced is shared with the host, which itself provides the algae with minerals and shelter. Periodically this coral’s surface layer of tissue is shed, appearing to be a mechanism for ridding the colony of unwanted algal growth.
Colonies of Alcyoniidae are fairly stable around the Great Barrier Reef. Little predation is found in this family. A study conducted over a three year period also showed little growth rate, reproduction and mortality in these corals; and only a few new colonies came into existence during that time.
There are 24 known genera of the Alcyoniidae family.