Award: OCE-1357327

What factors determine the abundance and fluctuations of marine bottom organisms? For a long time, it has been understood that identifying the processes that influence the young is key to answering this question. Thus, a fundamental question in marine science is how the larvae, or early life stages, of bottom marine organisms that develop in the ocean, are transported to nearshore coastal habitats to complete the life cycle. Such understanding is critical for understanding how populations fluctuate, for determining the placement of marine reserves, and for managing commercially important species such as crabs and lobsters. In the past, researchers have focused on how open-ocean offshore processes influence the distribution and transport of larvae of shallow water species. A series of studies during the last two decades indicate, however, that most larvae stay close to shallow water. Thus, an exclusive focus on offshore processes in the last few decades might have been misplaced. To gain knowledge on the ocean currents affecting the larvae, their distribution near the shallow adult habitat, and to better understand the mechanisms responsible for larval transport to shore, we undertook a two-year (2014-2015) study to quantify the number of larvae in the water column at five stations within 1 km of shore. We also measured water temperature, currents, and wave height, and counted the number of barnacle larvae settling in nearshore intertidal habitats. Barnacle larvae serve as a good proxy for other species, as they have a similar life cycle to those of many bottom organisms. Our study produced two significant findings, potentially breakthroughs. First, the separation between the minuscule larvae and the adult habitat was related to thermal stratification –the difference in temperature between surface and bottom waters. With larger differences, or greater stratification, the larvae were found closer to the shore. This is an intuitive result, because large temperature differences are associated with flows that reverse with depth, and it is known that larvae exploit these flows to control their distribution around the adult habitat. However, to our knowledge this is the first study that has resolved this issue. Second, we identified an area between offshore waters and the zone where the waves break where larvae accumulate, and that the abundance of larvae that settled on the shore is correlated with that in the ?zone of accumulation?. This suggests that the processes that cause this area to grow or dissipate may control how many larvae are supplied to adult habitats, a significant finding. All fieldwork and sample processing was conducted using facilities and resources at the University of San Diego (USD), a primarily undergraduate institution. This project had broad participation, providing research experiences and training for 12 undergraduate students, 6 graduate students, and 6 technicians. A Woods Hole Oceanographic Institution (WHOI) postdoctoral scholar completed research based on ideas spun from the grant. Two under-represented high school students conducted summer research, and two undergraduate Honors Theses were produced from this work, including a collaborative project that used DNA barcoding to identify fish eggs collected in our larval samples, and extended the scope of this research beyond invertebrate larvae. Two M.S. theses were completed resulting in three manuscripts with graduate student authors. Data collected in these projects were used to develop undergraduate curriculum at USD. We disseminated results widely, through presentations at national and international conferences, including those authored by undergraduate and graduate students, as well as though peer-reviewed publications. Last Modified: 02/23/2019 Submitted by: Nathalie Reyns