Caribbean sea-fan mortalities

Epizootics resulting in mass mortalities of Caribbean sea fans have been observed for more than 15 years, but the cause has remained unresolved. Here we report for the first time the presence of a putative pathogen associated with diseased sea-fan tissue throughout the Caribbean. We obtained samples of healthy and diseased Gorgonia ventalina and G. flabellum (Cnidaria: Gorgoniidae) from the Bahamas, the British Virgin Islands, Curacao, Saba and Trinidad. We examined samples preserved in ethanol (80-100%) under the microscope. Diseased samples showed distinct recession of rind tissue (coenenchyme, the outer organic rich matrix containing the living polyps), exposing the axial skeleton (dead central core). The exposed core was often colonized with a cyanobacterium similar to Phormidium corallyticum, the organism responsible for black-band disease in hard corals. Although this colonization of the core on some samples was extensive, it appeared secondary to the recession caused by the fungus. In all diseased samples, we observed hyphae embedded in the receding edge of the rind. Hyphae were not seen in healthy rind tissue.