KOEHL, M. A. R. *; HADFIELD, M. G.; Univ. of California, Berkeley; Univ. of Hawaii: Dissolved chemical cues affect retention and attachment of larvae within coral reefs

Can dissolved chemical cues released by organisms on the substratum affect larval settlement in turbulent, wave-dominated flow typical of many shallow coastal areas? We addressed this question using larvae of the sea slug, Phestilla sibogae, which settle in response to a water-borne species-specific metabolite of their prey, Porites compressa abundant corals forming reefs in shallow habitats in Hawaii. Field measurements showed orbital wave-driven flow above reefs, slower oscillatory water movement through reefs, and net flow of water upwards from coral heads and downwards into depressions in the reef. Competent larvae are induced to cease swimming and sink by water collected within and just above reefs. Field releases of larval mimics showed that sinking enhances their retention in the water within a reef; capture of mimics on sticky surfaces mounted on coral branches revealed that most mimics landed within the seaward and middle portions of reefs. Several years of monitoring P. sibogae recruitment revealed similar spatial patterns. Flow tank measurements of larval adhesion to surfaces showed that cue is required for larvae to attach to the substratum. When in cue, the shear strength of larval adhesion to coralline algae encrusting surfaces within a reef is as high as to P. compressa.