Comparison of anti-predatory defenses of Red Sea and Caribbean sponges. I. Chemical defense

Among marine invertebrates, sponges produce the largest number and diversity of novel secondary metabolites, some of which are used as defenses against predation. Seventeen abundant Red Sea sponge species were assayed for their ability to deter predation by 2 common Red Sea generalist predators: the fish Thalassoma klunzingeri and the sea urchin Diadema setosum. In addition, 17 common Caribbean sponge species were tested against both the Caribbean wrasse T. bifasciatum and the Red Sea wrasse T. klunzingeri. Among the 17 Red Sea species tested, 7 (41%) deterred T. klunzingeri. Extracts from the 17 Caribbean sponge species spanned a range of activities, from highly deterrent to highly palatable, when tested against both fish predators. Extracts were either deterrent to both fish species or palatable to both, suggesting that there are general responses by fish predators to deterrent sponge metabolites, regardless of geographic origin. Of the 17 Red Sea sponge species, 11 (65%) produced extracts deterrent to the sea urchin Diadema setosum. The same 7 species that deterred fish also deterred sea urchins, with 4 additional sponge species affecting only the sea urchins. Sea urchins were either deterred by different metabolites than fish or are more sensitive and thus are deterred by the same metabolites but at lower concentrations. Extracts from endosome and ectosome layers of 6 Red Sea sponges showed no difference in their ability to deter predation by T. klunzingeri and D. setosum, contrary to the prediction of the optimal defense theory.