Award: OCE-0961830

Boundaries in the ocean and the disadvantages of having a long larval life On land, it is easy to imagine that some species cannot reach some places. A mountain, a desert, a river—depending on the organism, these or other landscape features can act as barriers to movement. But what stops organisms in the ocean? Although ocean waters appear to connect all marine habitats, different regions have water masses with different properties, and the associated variation in temperature, salinity or nutrients may affect species distribution. Traditionally, temperature has been viewed as the most important factor to explain distribution of species in the ocean, but recent studies suggest that currents also play an important role (Fig 1). Ocean currents can transport spores, eggs and larvae of marine species. Many marine invertebrates have a larval stage in their life cycle, which can last from days to months, during which they drift or swim in the ocean. It is generally accepted that greater time spent in the water is associated with greater dispersal distance. But more time in the water also means more time to be negatively affected by bad currents. Depending on their direction and pattern of circulation, currents can carry the tiny larvae far from suitable habitat, and thus act as a boundary between ocean areas. If currents are important to explain boundaries in the coastal ocean, we would expect more boundaries for those species with larvae that stay in the water for a longer period, and the distribution of species boundaries in the ocean to be related to the pattern of circulation. To explore these ideas and understand better what determines species boundaries in the coastal ocean, we analyzed the distributions of ~1800 marine invertebrates (crustaceans, mollusks, annelids, echinoderms and cnidarians) along the eastern coast of North America. We gathered information on depth distribution of the species—that is, whether they inhabit shallow or deep waters—and we classified species by "short" or "long" larval duration, depending on the time that larvae spend in the water to complete development (Fig 2). Did all species have the same chance of being affected by a boundary? No. Species with different characteristics showed different locations of boundaries. Some locations along the coast had more boundaries for shallow species; some locations were more important barriers for deep species. When comparing similar locations, we found more boundaries blocking movement from south to north than from north to south. Looking closer at the northern boundaries, we found, as expected, more boundaries in species with long larval duration (Fig 3). Overall, our results suggest that the pattern of circulation can affect the location of range boundaries, particularly in species with long larval duration. The consistency of these current patterns and their strong effect on larvae can explain why species boundaries of so many different species are concentrated in narrow portions of the coast. Also these currents can affect the evolution of larval dispersal strategies because some hydrodynamic environments will make some strategies unviable. Furthermore, the constraints set by currents will affect how climate change influences species distributions, which may depend not only on changes in ocean temperature, but also in ocean circulation. Broader impacts: Eight publications will result from this project. Also, we have used this work to shape an Honors evolution class on the interaction of climate change, biogeography, and evolutionary dynamics with a publically-accessible web resource: (http://pisaster.genetics.uga.edu/groups/evolution3000/ ). We posted a popular synopsis of our work on species distribution ranges on the Ecography Blog: (http://www.ecography.org/blog). Also, a presentation summarizing our range work is posted on the Faculty of 1000 Posters: http://f1000.com/posters/browse/summary/1097501 We...