"Like rich rosettes of royal velvet, they decorate the rusting iron, transforming the unromantic metal stanchions into pillars that would grace a palace"
wrote Robert Gibbings on observing soft corals for the first time on his visit to Hurghada in 1938.
This beautiful soft coral is on the wreck of the Carnatic in the Red Sea. She was a sail and steam ship launched in 1862. Seven years later she struck the reef. For two days she remained there with all passengers and crew staying on board. They finally abandoned ship, but as they were doing so the Carnatic broke in half. Thirty-one people died but the rest reached the lifeboats and Shadwan Island.
The coral is Dendronephthya hemprichi. This species is a pioneer settler. It can clone small fragments of itself with root-like processes that quickly attach to artificial structures like wrecks. Especially vertical structures.
D. hemprichi on the Numidia wreck
As well as cloning itself, this soft coral reproduces sexually year round. They don't have synchronised broadcast spawning episodes, as many other corals do. They also reproduce at a younger age than other corals. Spawning occurs after sunset and continues until 2 am.
One of the Nephtheidae family, the soft coral takes in sea water to expand its body before feeding. This builds up a positive pressure inside the coral that supports the branches and trunk.
Another difference between D. hemprichi and other corals, is that they don't depend on symbiotic algae: they are azooxanthellate (asymbiotic). Instead they feed almost exclusively on phytoplankton. Eight feathery tentacles surround the coral's mouth and whip food into it. Relatively recent data on soft corals indicates that they feed on very small plankton such as single-celled algae, rather than larger particles as had previously been thought.
According to the Encyclopedia of Life, Dendronephthya are among the most commonly traded soft corals. Between 1988 and 2002 at least 12,618 were sold globally (the U.S. was the largest importer, with 51% of the total Dendronephthya trade). However, corals in this genus are poor choices for aquarium hobbyists. They generally die within a few weeks, mainly because they rely on filtering food particles and dissolved nutrients from the water.
Soft coral by Tim Nicholson.
Until recently soft corals were not thought to be reef-building, although they do secrete limestone. In their case this is as internal crystals called sclerites or spicules (yellow in the photo above). New research though has revealed that massive parts of coral reefs are actually made from cemented sclerites.
Because soft corals do not have large skeletons, they grow faster than hard corals
You find Dendronephthya hemprichi from around 11 to 32 m, standing out from walls and wrecks in currents.
Phylum: Cnidaria > Class: Anthozoa > Subclass: Octocorallia > Order: Alcyonacea
References and Further Reading
Soft coral is reef building, SCUBA News
Blue Angels and Whales, by Robert Gibbings 1938
K Fabricus, Y Benayahu, A Genin, Herbivory in Asymbiotic Soft Corals. Science, April 1995, Volume 268
M Dahan, Y Benayahu. Clonal propagation by azooxanthellate octocoral Dendronephthya hemprichi. Coral Reefs (1997) 16:5-12
U. Oren, Y. Benayahu, Transplantation of juvenile corals: a new approach for enhancing colonization of artificial reefs. Marine Biology, February 1997, Volume 127, Issue 3, pp 499-505