Award: OCE-1357033

NSF AWARD OCE-1356966 TURBULENCE-SPURRED SETTLEMENT: DECIPHERING A NEWLY RECOGNIZED CLASS OF LARVAL RESPONSE PROJECT OUTCOMES A dominant majority of shoreline-dwelling animals in the ocean produce microscopic offspring that live for days to months in the plankton, drifting in waters offshore of the coast. These tiny larval stages often look completely different in form compared to the juveniles and adults that they grow into, and which inhabit the rocky shores and beaches with which most people interface. The transition between these two stages is therefore one of the most notable and crucial steps in the life cycles of organisms in the sea. In the research conducted by means of this grant, our team explored the transition that tiny larvae take in moving from the plankton to the shore, focusing in particular on sea urchins and their kin. Our efforts were directed at understanding details of a recent discovery that we made just before the grant was awarded. We found that the attainment of ?competency,? the ability of larvae to respond to chemical cues indicative of suitable habitat on the shore, can be triggered by physical attributes of the environment. More specifically, we determined that exposure of sea urchin larvae to intense turbulence characteristic of wave-exposed coasts preferred by adults could cause the larvae to precociously enter the competent state. Previously it had been thought that the timing of competency was determined simply by a hard-wired and therefore largely immutable developmental program. Learning that larvae at this key life transition are notably sensitive to a range of environmental experiences has important implications. For example, knowledge concerning potential triggers of competency could substantially modify our understanding of how populations of ecologically and commercially valuable species like sea urchins -- one of several invertebrates fished for human food -- are maintained. We highlight here several novel findings that originated from this grant. First, we documented through laboratory experiments that the turbulence response exhibited by a particular type of sea urchin (Strongylocentrotus purpuratus, the purple sea urchin) is not unique to just that species. Other types of sea urchins, as well as a more distantly related invertebrate, the Pacific sand dollar, show a similar reaction to turbulence, in that the progression to competency is accelerated as a result of just a few minutes of exposure to intense turbulence. This early shift to competency can shorten the minimum time spent in the water column by 20%. Interestingly, the response is not universal in sea urchins nor is it limited to only urchins. Several urchin species that we have tested whose adults dwell in deeper habitats where turbulence is weaker do not show any acceleration in competency in response to turbulence. On the other hand, turbulence does appear to influence the manifestation of competency in more distantly related species, including a brittle star and marine snail. Second, we demonstrated that the level of responsiveness of larvae to turbulence, and thus their propensity to become competent following such an environmental stimulus, increases as they get older. This phenomenon includes a tendency for larvae to become less choosy about habitat. At the same time, larvae that transition early to shoreline habitat bear a cost in that they are smaller and thus more vulnerable to physical stressors and predators. A third finding of our research is that the response of larvae to turbulence can be long-lasting. Larvae that experience intense turbulence, but which then are placed back into quiescent waters, do not regress to their original condition; rather, they remain competent. This result suggests a physiological change that is not readily reversible. Fourth, we have indications of population-level genetic variation in the turbulence response. The project additionally contributed to the advancement of several graduate students who were supported by the grant, led to results covered by the popular media, and funded a freely-accessible web-based educational module on the VirtualUrchin platform (http://virtualurchin.org) that serves hundreds of thousands of secondary school students yearly. Specifically, we produced a new interactive educational game for VirtualUrchin based upon our research called 'Surfing to Settlement', where the student controls a larval avatar that needs to find food and grow and ultimately locate a safe place to settle near to its kin, while avoiding planktonic predators and excessive offshore drift. Together these research efforts have advanced our understanding of one of the most important life cycle transitions characterizing marine species, including a number that people rely on for food. Last Modified: 06/10/2018 Submitted by: Christopher Lowe