Fungal disease resistance of Caribbean sea fan corals (Gorgonia spp.)

An on-going, Caribbean-wide epizootic affecting sea fan corals (Gorgonia sp p.) is caused by the fungus Aspergillus sydowii (Thom et Church). We examin ed the role of crude extracts in resistance of two species of sea fans, Gor gonia ventalina (L.) and G. flabellum (L.), against A. sydowii and a bacter ial pathogen of fish, Listonella anguillarum (MacDonell et Colwell). Sea fa ns were collected in January 1997 from San Salvador, Bahamas, and in June 1 997 and January 1998 from Alligator Reef, Florida Keys, USA. Crude extracts from both species were tested to determine concentrations inhibiting germi nation of A. sydowii spores. Crude extracts from both species inhibited spo re germination at concentrations as low as 1.5 mg ml(-1); most samples were active at 5 to 10 mg ml(-1). These concentrations are within the range est imated in living tissue and were higher in healthy colonies suggesting thei r role in mediating disease susceptibility. We also detected within-colony gradients in antifungal activity, which varied with the disease state of th e colony. In healthy sea fans, resistance was highest at colony edges and l owest in medial and central regions of the colony. Among sea fans with lesi ons in the colony center, resistance in tissue from proximal and medial reg ions was as high as tissue from the colony edge (i.e. distal region). The i ncrease in antifungal activity suggests an inducible response by the coral host to the fungal pathogen. This response is most evident among sea fans w ith lesions in the colony center and not among colonies with lesions at the edge. Antibacterial activity of crude extracts against L. anguillarum was highest at the colony edge but did not vary with disease state or tissue lo cation.