EXBODI / The brittlestar and the gorgonian
18 September 2011
We very often collect organisms that live in association in our trawls. Gorgonians, in particular are often associated with numerous benthic animals.
In the Southeastern part of the New Caledonian EEZ, we very often find brittlestars (echinoderms related to starfish) that cling to gorgonian branches. This perched position is undoubtedly advantageous for the brittlestar, which is then exposed to stronger water currents, and can therefore capture more particles in suspension in the water column for nutrition.
These associations can be very specific, some species of gorgonians and brittlestars, such as the gorgonian Metallogorgia melanotrichos and the brittlestar Ophiocreas oedipus, apparently never leave each other. Organisms of these species live and grow old together!
There is a great diversity of associations between corals and other benthic animals. Some fish and cephalopods lay their eggs between the branches of gorgonians, some barnacles cling to bare parts, shrimp take shelter there, some crustacea and pycnogonids (sea spiders) live inside the polyps (the mouths of the corals)...
In the collections from the explorations of the New Caledonian slope, we have shown that one species of corals (Chrysogorgia sp.) harbors tens of small anemones. These latter wrap their around the branches of the coral. This association, very rarely reported in the literature, was only known based on specimens of bamboo corals collected in New Guinea.
Our collections suggest that this association could be more common than we thought and could correspond to an example of commensalism (in competition for food). We can find other examples of more classical parasitism, such as fish and copepods.
For further information
Watling L, France SC, Pante E, Simpson A (2011) Biology of deep-water octocorals. Advances in Marine Biology 60: 41-123