Meeting Abstract
Seashore marine organisms with a planktonic dispersal phase can release millions of offspring in their lifetimes, a tiny fraction of which survive to become juveniles back on the seafloor. One notable bottleneck in such life histories for benthic animals and algae is for the larva or dispersive stage to locate an appropriate place to settle into the benthos. Therefore, we predict that planktonic stages are under significant selection pressure to acquire the capacity to respond to any environmental signal that may indicate suitable benthic habitat. We have previously shown that one such signal for nearshore sea urchin and sand dollar larvae is fluid turbulence, which increases in intensity near coastlines, and exposure to these increased levels propels larvae from a non-responsive pre-competent period into a competent stage, where the larvae can respond to local cues and settle. Nevertheless, many such species exist as adults in highly specific benthic habitats that are far more rarely encountered than the associated turbulence conditions, which characterize broader habitat scales. Here we provide an account for this apparent mismatch in signal consonance at different scales: turbulence exposure seems to cause sand dollar (Dendraster excentricus) larvae to permanently shift from pre-competence to competence. This observation suggests a scenario where turbulence can activate a temporally extensive search image in larvae over a broad habitat range, a plausibly adaptive feature for larvae entering dynamic coastal environments. We also describe preliminary results indicating that sand dollars show population level variation in larval responsiveness to turbulence, thus suggesting scope for adaptation at this crucial planktonic-to-benthic transition.
