POPULATION-STRUCTURE AND FEEDING DETERRENCE IN 3 SHALLOW-WATER ANTARCTIC SOFT CORALS

Alcyonium paessleri and Clavularia frankliniana are numerically abunda nt soft corals in the nearshore (12 to 33 m depth) benthic communities of eastern McMurdo Sound. They are much less abundant in western McMu rdo Sound where a third species, Gersemia antarctica, co-occurs in low numbers. The body tissues of these three species are comprised mainly of organic material (53 to 70% dry wt), which is primarily dervied fr om NaOH-soluble protein and refractory material. The energetic content s of the whole-body tissues of A. paessleri, C. frankliniana and G. an tarctica are 15.9, 17.3, and 14.5 kJ g(-1) dry wt, respectively. The m ean biomass per individual is 1.81, 0.008, and 45 g dry wt for each re spective species. Based on population densities of 7.3, 1337.3, and 0. 04 soft corals m(-2) for A. paessleri, C. frankliniana and G. antarcti ca, respectively, the population energetic densities are estimated to be 210.1, 185.1, and 26.1 kJ m(-2). Despite the relatively rich energe tic content of the tissue and apparent vulnerability to predators, ver y little predation occurs on these soft corals. Two potential predator s, the antarctic sea stars Perknaster fuscus and Odontaster validus, e xhibited significant chemotactic defensive tube-foot retractions to he xane, chloroform, methanol, and aqueous methanol extracts of each soft coral. In addition, whole-body tissue of each soft coral was rejected by the demersal fish Pseudotrematomus bernacchii and the cryopelagic fish Pagothenia borchgrevinki. In contrast, whole soft-coral tissues s equentially extracted in four increasingly polar solvents were readily ingested by these antarctic fishes, indicating that sclerites do not play a significant role in deterring predators. Our results indicate t hat these antarctic soft corals contain bioactive compounds which dete r common predatory seastars and fishes.