Collaborative Research: Improving quantification of larval dispersal in the global coastal ocean to understand the genetic structure, biogeography, and spread of benthic organisms

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The offspring or larvae of many marine species are carried or dispersed by ocean currents. This dispersal impacts where species persist, their genetic variability in space, and how they can spread to new locations as climate changes. This project uses a modern model of global ocean currents to quantify this dispersal and to explore how currents affect it. The novelty of this approach comes from the high spatial resolution of the simulated currents and their variability. The detailed estimates of dispersal are compared to observed pathways traveled by drifters and against information of species distributions and of their genetic variability. Most prior efforts ignored ocean currents to estimate dispersal, using instead the time that offspring are floating in the water. When the ocean currents were in fact considered, the delivery of larvae to the coast from offshore was the main focus, rather than transport occurring along the shore. This project addresses both deficiencies and enables examination of the effect of dispersal on the distribution of coastal species space at a global scale. The project includes the development of software tools and data sets, along with training videos, that allow researchers, ecosystem managers, environmental agencies, and other interested parties to model dispersal for different dates and locations on their own. Two PhD and six undergraduate students are being trained for scientific careers by having them develop related inter-disciplinary investigations, spanning from marine ecology to numerical modeling and physical oceanography. This project uses a modern high-resolution global model to explain how larval dispersal of coastal marine species quantitatively affects the biogeography, phylogeography, and invasibility of coastal oceans globally. The project is innovative in that oceanographically realistic estimates of alongshore dispersal, including the magnitude and spatial variability of ocean currents, are tested against existing large-scale datasets. Products include tools that allow the research community to easily estimate the dispersal of larvae along the coast of the global ocean, replacing the crude, and often incorrect, estimates that have dominated approaches to date. Dispersal paths calculated with currents from the Mercator 1/12 degree data-assimilative global circulation model are validated against surface drifter data from the Global Drifter Project. This new dispersal data is used to determine the role of alongshore variation in larval dispersal on 1) the magnitude of genetic estimates of connectivity, 2) the location of biogeographic boundaries, and 3) the variation in susceptibility of open coastlines around the world to invasive species with planktonic larvae. This study improves on previous studies by quantifying the distance larvae are transported alongshore by ocean currents in the offshore larval pool, allowing an examination of how dispersal affects spatial structuring within and among species at a global scale. Global, place-based quantification of the influence of oceanography on dispersal deepens the understanding of the role currents play in species distributions. In turn, understanding the regional differences in the importance of dispersal helps predict regionally specific responses of species to changing conditions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.