Meeting Abstract

5.2  Wednesday, Jan. 4  When settlement doesn’t settle it: the pitfalls of still-water larval assays LOH, T.-L.*; PAWLIK, J.R.; University of North Carolina Wilmington; University of North Carolina Wilmington

For many marine sessile invertebrates, the swimming larva is the sole motile phase in the organism’s life cycle. Much research has been focused on the larva’s ability to select an optimal substratum for settlement, using a variety of physical and chemical cues that are attributed to specific substrata. Various chemical cues have been shown to induce settlement, the attachment of the larva to the substratum, and sometimes metamorphosis, at a higher rate than in controls. However these results may not indicate an adaptive response to the extracts, instead representing an artifactual result of perfusing larvae with high concentrations of a bioactive metabolite that they may never encounter at similar concentrations in nature. We observed that the larvae of the Caribbean Orange Icing Sponge, Mycale laevis, settled rapidly in response to the presence of freshly cut pieces of the sponge Amphimedon compressa in still-water assays. Because A. compressa is chemically defended from fish predation, we tested the hypothesis that the palatable M. laevis preferentially settles on A. compressa for associational defense. However, when the experiment was repeated with pieces of A. compressa that had healed before assays, the larvae of M. laevis did not settle. Sponge ‘juice’ squeezed from A. compressa induced faster settlement and metamorphosis of the larvae compared to controls, but at higher concentrations, the settled larvae died within 48 hours of exposure to the ‘juice’, and never developed to the ‘flattened’ stage seen in the controls. Rather than inducing normal settlement, secondary metabolites from A. compressa trigger metamorphic changes in larvae of M. laevis that are probably unrelated to any natural response