Award: OCE-1334553

This project is two-pronged. The biological oceanography portion (based at Bodega Marine Laboratory) addresses how transport of larvae in the ocean is affected by their behavior. The technological aspect (based at NC State University) addresses a roadblock to studying transport of living larvae in the ocean: the impossibility of tracking them. We use a "robot larva" that mimics larval behaviors and resultant drift, and can be tracked. Intellectual Merit How microscopic larvae are transported by ocean currents is no small matter. Most marine invertebrates, and even fishes, reproduce by releasing tiny offspring into the surrounding water. They typically are weak swimmers while small, and go where the water is going. To become part of the next generation, they must be transported to appropriate habitats to take on adult forms and ecological roles. Whether they succeed has huge implications for choosing the location and size of Marine Protected Areas as sources to repopulate depleted or overfished habitats, and for fisheries management (does larval mixing make this a single population, or several isolated stocks?) Larval transport also affects how fast invasive species spread, and how resilient species are to changing climate—can they move as fast as physical zones are shifting? What if the water into which larvae were released is not going where they need to go? Water motion isn?t homogeneous, and behavior gives even weakly-swimming larvae options to affect transport by migrating vertically into different layers of water moving at different velocities or different directions. At NCSU we developed a novel biomimetic instrument, the Autonomous Behaving Lagrangian Explorer (ABLE,) to serve as a "trackable robotic larva." ABLEs sense their physical microenvironment, log the data, and use the data to dynamically calculate the target depth toward which they migrate according to a behavioral model based on real larvae. Multiple tracking modalities permit recovery even in rough sea states: a pinger while submerged, LED and VHF beacons while at the surface, and GPS coordinates sent to satellites during brief excursions to the surface. ABLEs run for 3 weeks on a battery charge (similar to the larval lifetime of many species.) They are optimized for simplicity and low cost (<$1K each,) since drifter studies require that numerous replicates be deployed at once. ABLEs were further refined as ocean experiments subjected them to challenges they had not faced in a tank or pool. At BML, field experiments were conducted in an upwelling region on the central California coast. Prevailing winds drive surface waters offshore, and draw up colder, nutrient-rich water from the depths into the sunlit surface layers. This supports some of the highest levels of plant (phytoplankton) and hence animal productivity in the world?s oceans. In upwelling currents, larvae that remain near the surface would be expected to be swept downwind and offshore (southwest,) be carried out to sea, and be lost. In contrast, observations show that they typically remain within a few km of the adult habitats where they were released. This could not occur if they were remaining at a fixed depth; vertical migratory behavior must be involved. To assess effects of vertical migratory behaviors, ABLEs were released at various sites, programmed with theoretical or observed larval behavioral patterns, and tracked for 1-2 days. Several hypotheses were tested, and the ABLE trajectories were consistent with each. 1. Larvae that remain near-surface during upwelling would be transported SW and offshore with surface waters. ABLEs at 2m went in that direction at several km/day. 2. When upwelling stops, as denser upwelled water sloshes back down (the system "relaxes,") larvae that remain near the surface would be transported northward and inshore. ABLEs at 2m went north at several km/day and were recovered close to shore. 3. Larvae that remain near the bottom would be transported shorter distances under either upwelling or relaxation conditions. ABLEs remaining at 16m bore this out. 4. Larvae that perform daily vertical migrations (up at night, deep during the day) would experience transport intermediate between that of near-surface and near-bottom larvae. The distance they were transported would be particularly affected by wind speeds during the night, when they were in the wind-driven surface layer. ABLEs migrating between 2m and 16m showed intermediate, and highly variable, speed of transport. Broader Impacts The results from field experiments are directly relevant to resource and MPA management. Collaborators at the Bodega Marine Laboratory, technicians and students have been trained to use this novel technology. The demonstration that ABLEs can address transport questions in many coastal/estuarine systems has generated interest from other potential users and manufacturers, and we look forward to new areas of inquiry opening. Exposure of the project in various articles, particularly the award-winning PBS "Science Friday" spot, has fostered public interest in science. Last Modified: 12/11/2017 Submitted by: Thomas G Wolcott