Biochemical composition of Caribbean gorgonians: Implications for gorgonian - Symbiodinium symbiosis and ecology

Gorgonian corals are the dominant benthic fauna on many Caribbean reefs, and yet studies on the makeup of the host, or their dinoflagellate symbionts, Symbiodinium spp., are scarce. We investigated the biochemical composition and symbiont parameters in eight gorgonian coral species. Skeletal material, comprised of sclerites and refractory material, was the largest component of gorgonian branches. Relative amounts of sclerites and refractory material varied between species and may explain species level differences in branch flexibility. In gorgonian branches, proteins, present in refractory and cellular material, made up the largest component of organic matter, followed by lipids, while carbohydrates were a minor component. The lipid content in gorgonian organic matter was significantly correlated with Symbiodinium density. In addition, symbiont density in gorgonian branches was probably influenced by the availability of host cells. Knowledge about biochemical parameters of gorgonian corals at ambient environmental conditions will assist in understanding the abundant benthic fauna of many Caribbean coral reefs.