Koehl, M.* A. R. *; Hadfield, M.G.; Cooper, T.; Reidenbach, M.A.; Koseff, J.R.: Can Larvae of Benthic Animals Use Dissolved Chemical Cues in Wave-Driven Flow?

Can chemical cues in the water affect the settlement of larvae of benthic marine invertebrates in habitats subjected to the wave-driven water flow that characterizes many coastal habitats? We addressed this question using larvae of the sea slug Phestilla sibogae, which metamorphose in response to a water-borne species-specific metabolite of their prey, Poritescompressa. P. compressa is an abundant coral that forms reefs in shallow, wave-dominated habitats in Hawaii. We used dye releases and acoustic doppler velocimetry to characterize the water flow above and within P. compressa reefs. A flow regime mimicking the turbulence and waves measured in the field was created in a flume across a reef of P. compressa skeletons; planar laser-induced fluorescence was used to quantify the filamentous small-scale spatial and temporal distribution of cue concentrations above the reef. Tethered larvae swimming in a mini-flume exposed to temporal patterns of cue mimicking those above a reef, rapidly retracted their ciliated velum (the swimming organ) when in filaments of cue. Larval bioassays of cue strength in field-collected water elucidated patterns in the locations on a reef where water-borne chemical cues are strong enough to induce P. sibogae larvae to stop swimming and sink. A series of field experiments monitoring the transport of larval mimics showed that P. sibogae larvae sink rapidly enough to be retained on the reef when wave-driven flow moves across it.