No accounting for taste: Palatability of variably defended Caribbean sponge species is unrelated to predator abundance

Abstract

The antipredatory chemical ecology of Caribbean reef sponges has been well studied, with two distinct ecological strategies described: chemically defended species use secondary metabolites to deter fish predators, while palatable species lack chemical defenses, but grow, reproduce, or recruit fast enough to persist despite predation. While most palatable sponge species are consistently undefended from fish predators in laboratory feeding assays, there are some species that exhibit individual inter- and intra-site variation ranging from palatable to defended. The objective of this study was to better document the extent of chemical defense variability for 7 of these species over a wider geographic range and to test the dual hypotheses that variably defended sponge species would be (1) more palatable, and (2) exhibit greater variability in chemical defenses from reefs without sponge predators than from reefs where predators are abundant. Laboratory feeding assays using the bluehead wrasse confirmed intraspecific variability of chemical defenses for Clathria virgultosa, Cribrochalina vasculum, Desmapsamma anchorata, Dragmacidon reticulata, Iotrochota birotulata, Niphates digitalis, and Xestospongia muta for sites across the Caribbean. Surprisingly, logistic regression models relating levels of sponge chemical defense to a site-specific index of spongivorous fish abundance offered little support for the hypothesis that predator abundance alters palatability for any of these variably defended sponge species. The presence of symbiotic zoanthids in the tissue of I. birotulata and N. digitalis did not alter palatability. While the selective effect of predation has segregated most species of Caribbean reef sponges into chemically defended and undefended categories, this study concludes that the situation is more complex for variably defended sponge species, and suggests that automimicry is a possible explanation for this alternative strategy.