Dendronephthya hemprichi, fed extensively on phytoplankton, gaining more than enough carbon to cover respiration and growth requirements (Fabricius et al., 1995b). Although this species also fed on zooplankton, only 2.4-3.5% of the daily carbon requirement of this coral was met by ingesting zooplankton. Three other asymbiotic Red Sea octocorals, D. sinaiensis, Scleronephthya corymbosa and the gorgonian Acabaria were also found to contain large quantities of phytoplankton in their gastrovascular cavities (Fabricius et al., 1995a). Adaptations for phytoplankton capture include the small spaces between the pinnules of D. hemprichi, which appear to be ideal for straining phytoplankton from flowing waters. The large spicules found in the body column and around the polyps of Dendronephthya spp., appear to function more in holding the column and polyps erect in strong current flows, than as protection against predation, allowing them to strain phytoplankton effectively from the passing waters (Fabricius et al., 1995b). Some of the most impressive growths of Dendronephthya spp. are often found on ship wrecks in the South Pacific, where structures high above the bottom and projecting into the current are often heavily encaisted! It is tempting to equate this with oyster hatcheries, where oysters are hung in cages well above the bottom and within strong currents. Both organisms feed on phytoplankton, and hence benefit from these positions by being exposed to maximal phytoplankton concentrations because of the high volume of water flowing past them. In light of this new evidence, scientists need to re-evaluate the role of phytoplankton in the nutrition of other octocorals. Several studies are now underway to determine to what extent both zooxanthellate and azooxanthellate species actually feed on phytoplankton.
Another mode of feeding may be the trapping of mucus floes often called marine "snow". These are composed of detritus, bacteria, protozoans and possibly phytoplankton trapped in mucus. The source of the mucus floes may be organic substances released on a regular basis by soft and stony corals to rid themselves of epizoic growths and excess carbon and fats. This material is not quickly degraded by bacteria and it is often infested with large quantities of bacteria and eukaryotes (flagellates, cili-ates and diatoms) (Vacelet and Thomassin, 1991). These mucus floes could be trapped by the spiky polyps of Dendronephthya spp. and used as a food source. To the best of our knowledge no one has investigated the possible role of this material in octocoral nutrition, but it is easy to see that it becomes trapped on the spiny projections of the surface of many octocoral species.
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