Indirect effects of bleaching on predator deterrence in the tropical Pacific soft coral Sinularia maxima

The environmental stress theory (EST) suggests that stress-induced biochemical changes will make an organism more susceptible to predation relative to unstressed individuals. Bleaching represents a stress response in marine invertebrate host-zooxanthellae symbiont associations, including those species that rely on chemical defenses to reduce predation pressure. We examined the EST in the context of a natural soft coral bleaching event, and then by use of a 3 mo transplant/shading field experiment that also resulted in bleaching. Feeding experiments using an omnivorous pufferfish indicated that extracts of bleached soft corals were more palatable to predators than were those from unbleached individuals. Two biochemical constituents were significantly reduced in naturally- and experimentally-bleached soft corals: lipid and defensive metabolite (pukalide) concentration. While a sunscreen (palythine) was significantly lower immediately after a natural bleaching event, it recovered and even exceeded pre-bleached levels in experimentally-bleached soft corals. Feeding assays with pukalide and lipid at concentrations representative of unbleached and bleached soft corals indicate that pufferfish are not deterred by bleached levels of the defensive metabolite, but that pufferfish are less attracted to food with bleached levels of lipid. Nonetheless, field observations of up to 4 times higher predation on bleached soft corals suggest that defensive metabolite concentration may have a greater influence on predation than food quality. This study indicates that a stress response (bleaching) has an indirect effect on predator deterrence in the soft coral Sinularia maxima due to changes in biochemical constituents that affect food quality.