Trade-offs in defensive metabolite production but not ecological function in healthy and diseased sponges

Diseases of marine organisms, and sponges in particular, are increasingly reported worldwide. Prior research indicates that the survival of sponges on reefs is due largely to their production of biologically active secondary metabolites that provide protection from a diversity of stressors. Aplysina Red Band Syndrome (ARBS) is an emerging disease affecting Caribbean rope sponges (Aplysina spp.), but it is not known whether secondary metabolites play a role in disease susceptibility and resistance. To investigate whether differences in secondary metabolites may explain variability in susceptibility to ARBS in Aplysina cauliformis, we used high performance liquid chromatography (HPLC) to generate chemical profiles from healthy tissue in both healthy and diseased sponges, and quantified peak areas for 15 metabolites. Analyses of healthy and diseased sponges revealed qualitative and quantitative differences in their chemical profiles. Aplysamine-1 and fistularin-3 were produced in significantly higher concentrations by healthy sponges, whereas aerothionin and 11-oxoaerothionin were found only in diseased sponges. At natural concentrations, extracts from both healthy and diseased sponges deterred feeding by an omnivorous reef fish. Fistularin-3 deterred feeding at concentrations found in healthy sponges, but not at concentrations found in diseased sponges. Aerothionin deterred feeding at concentrations found in diseased sponges, and may at least partially replace the loss of fistularin-3 as a feeding deterrent compound following pathogenesis, suggesting a trade-off in the production of feeding deterrent compounds. Extracts from healthy and diseased sponges inhibited bacterial growth, and both aplysamine-1 and fistularin-3 displayed selective antibacterial activity. Despite differences in secondary metabolite production between healthy and diseased sponges, the stress associated with ARBS does not appear to compromise the ability of A. cauliformis to maintain defenses against some of its natural enemies.