Assessing the antipredatory defensive strategies of Caribbean non-scleractinian zoantharians (Cnidaria): is the sting the only thing?

Abstract

The relative importance of chemical, nematocyst, and nutritional defenses was examined for 18 species of Caribbean sea anemones (actinarians), zoanthids, and mushroom polyps (corallimorpharians) from the Florida Keys and the Bahamas Islands, 2008–2010. Feeding assays were performed using the fish Thalassoma bifasciatum with artificial foods containing crude organic extracts of cnidarian tissues. A novel behavioral assay using brine shrimp nauplii was used to assess nematocyst defenses. The nutritional quality of cnidarian tissues was examined using bomb calorimetry and soluble protein assays. In general, actinarians invested in nematocyst defenses, zoanthids in either nematocyst or chemical defenses, and corallimorpharians lacked both, except for 1 of 3 species that was chemically defended. Relative to other coral reef invertebrates, cnidarian tissues had similar caloric values but lower soluble protein concentrations. Trade-offs between chemical and nematocyst defenses were observed for 65% of species, while habitat and behavior provided a likely explanation for undefended species.