Diet and seasonal prey capture rates in the Mediterranean red coral (Corallium rubrum L.)

Gorgonians are passive suspension feeders, contributing significantly to the energy flow of littoral ecosystems. More than in active suspension feeders (such as bivalves, ascidians and sponges) their prey capture is affected by spatial and temporal prey distribution and water movement. Corallium rubrum is a characteristic gorgonian of Mediterranean sublittoral hard bottom communities. This study found a high variability in the annual cycle of prey capture rate, prey size and ingested biomass, compared to other Mediterranean gorgonians. Detrital particulate organic matter (POM) was found throughout the year in the polyp guts and constituted the main proportion of the diet (25-44%). Crustacean fragments and copepods (14-46%) accounted for the second major proportion, while invertebrate eggs (9-15%) and phytoplankton (8-11%) constituted the smallest part of the diet. To verify the importance of detrital POM in the energy input of this precious octocoral species, in situ experiments were carried out during the winter-spring period. The results confirm the importance of detrital POM as the main source of food for C. rubrum [0.13 +/- 0.04 micro g C polyp-1 h-1 (mean +/- SD)]. This study also compares the prey capture rates of two colony size classes and two depth strata: Within the same patch, small colonies (10 cm high) (0.026 +/- 0.097 prey polyp-1 h-1) and showed a higher proportion of polyps containing prey (17% compared to 10%). Comparing colonies of similar size (