Fungal pathogenesis of the sea fan Gorgonia ventalina: direct and indirect consequences

Summary.

Fungal pathogenesis of the sea fan Gorgonia ventalina has developed on the Belize barrier reef during 1997 and 1998. The disease incidence (= percent of infected sea fans) remained unchanged at two sites along the barrier reef crest between years. However, the incidence increased significantly at an offshore atoll during that time, as did the virulence (= percent tissue loss). Grazing by the gorgonian specialist mollusc Cyphoma gibbosum increased on infected sea fans. Sea fan responses to fungal infection included significant decreases in a furano-germacrene compound with antifeedant activity and significant increases in the concentration of sclerites at the site of infection. Feeding assays utilizing C. gibbosum and a natural assemblage of reef fishes indicated sclerites are an effective deterrent, to both consumers, at both pre- and post-infected concentrations. In contrast, the compound was only deterrent to the fish, and only at concentrations found in pre-infected sea fans. These data indicate that sea fan pathogenesis can directly and indirectly affect population health via virulent tissue necrosis and pathogen-mediated reductions in grazer resistance, respectively.