Distribution of secondary metabolites in the sponge Oceanapia sp and its ecological implications

The Micronesian sponge Oceanapia sp. has an unusual growth form that consis ts of an irregular turnip-shaped base, which is buried in the substrate. On e to several fistules, which protrude through the sand, are attached to the base of the sponge. On top of each fistule is a small fragile capitum. We examined whether this conspicuous red-colored sponge was chemically defende d and if intraspecimen variation existed in the distribution of secondary m etabolites between different parts of the sponge. Furthermore we assessed t he deterrent properties of the secondary metabolites to generalist and more specialized fish predators. We also wanted to see if the optimal defense t heory holds in the case of a marine invertebrate. According to the theory, organisms evolve and allocate defenses in a way that maximizes individual f itness, assuming that defenses are costly to the fitness of the organisms. We were able to evaluate this hypothesis: since the different sponge parts in Oceanapia sp. were at different risk to damage by predators and had a di fferent value in terms of fitness loss to the sponge (the capitum probably plays a role in asexual propagation). Concentrations of crude organic extra ct increased from the base to the capitum of the sponge. The major secondar y metabolites kuanoniamine C and D also: showed a sharp increase from the b asal root to the capitum. There was no difference in structural material or ash content between the base and the fistule of the sponge, but fiber and protein content were significantly higher in the fistule. The methanol frac tion was highly deterrent in field feeding assays towards generalist reef f ish at base concentration. It also deterred feeding by the spongivorous ang elfish Pomacanthus imperator laboratory feeding experiments at the same con centration. The field feeding assays with pure compounds-showed that kuanon iamine C and D deterred feeding by-natural assemblages of reef fishes at fi stule concentrations, confirming their role as defensive agents. The intras pecimen variation of secondary metabolites in Ocennnpia spt supports the op timal defense theory by showing,the highest concentrations in those parts o f the sponge that are most visible to predators and are likely to be most i mportant for inclusive fitness.