ECOLOGICAL ROLES FOR WATER-BORNE METABOLITES FROM ANTARCTIC SOFT CORALS

Prior studies have documented predator deterrence and antifouling acti vities for organic extracts of the Antarctic soft corals Alcyonium pae ssleri and Gersemia antarctica under surficial contact situations. Fie ld observations and subsequent seawater collections support the releas e of waterborne allelochemicals by these 2 species. A. paessleri and G . antarctica released organics totaling 1.54 and 1.26 mg l(-1) of seaw ater extracted, respectively. The compounds from A. paessleri were com prised of 86% sterols by mass and they diluted to non-detectable level s within 1 to 2 cm of the colony surface. The absolute production rate s for the sterols varied positively with colony size and ranged from 3 .4 to 6.6 mg l(-1) seawater extracted d(-1). Three of the 4 sterols is olated from A. paessleri deterred seastar predators; included amongst these compounds was the primary metabolite, cholesterol. In contrast, G. antarctica released many classes of compounds and few in any major quantities. Nonetheless, the organic fraction of seawater collected ne ar this soft coral showed potent antibacterial activity against 3 symp atric microbes. Bioautography was used to guide isolation of the antim icrobial fraction which contained homarine, trigonelline, and a minor metabolite. Homarine was responsible for most of the bioactivity noted during the bioautography assay.