Ecological roles for water-borne metabolites from Antarctic soft corals

Prior studies have documented predator deterrence and antifouling activities for organic extracts of the Antarctic soft corals Alcyoniuni paessleri and Gersemia antarctica under surficial contact sltuatlons. Field observat~ons and subsequent seawater collt.ctions support the release of waterborne allelochemicals by these 2 species. A. paessleri and G. antarctica relcdsed organics totaling 1.54 and 1.26 mg I-' of seawater extracted, respectively. The compounds from A. paessleri were comprised of 8 6 % sterols by mass and they diluted to non-detectable levels within 1 to 2 cm of the colony surface. The absolute production rates for the sterols varled posllively with colony size and ranged from 3.4 to 6.6 mg I-' seawater extracted d.'. Three of the 4 sterols isolated from A. paessleri deterred seastar predators; Included amonysl these compounds was the primary nietabolite, cholest~rol. In contrast, G. antarctlca released many classes of con~pounds and few in any major quantities. Nonetheless, the organic fraction of seawater collected near this soft coral showed potent antibacterial activity dgainst 3 sympatric microbes. Bioautogi-aphy was used to guide isolation of the ant~microbial fraction which contained homarine, trigonelline, and a minor metabolite. Homarine was responsible for most of the bio-act~vity noted d u r ~n g the bioautography assay