The potentially important role that larval dispersal may play in determining gene flow, distributions, and population structure of marine invertebrates remains unclear despite many hundreds of descriptive comparisons of pelagic duration and population genetic structure. This lack of clarity suggests many factors may influence population genetic structure and their interactions may be complex. Difficulties studying these factors include (under normal circumstances) distinguishing local from exogenous recruitment and therefore the true distribution of dispersal distances. For example, experiments that normally could be undertaken to explore this issue are very small scale relative to the distances that many marine taxa may disperse.
In August 2011, a large-scale natural removal experiment was initiated along a 100 km stretch of the central California coast. The PIs propose to use this rare opportunity to clarify the effects of dispersal and species interactions on marine population genetic variation and community structure. They propose to study three species that suffered very high rates of mortality: an ecosystem engineer (Strongylocentrotus purpuratus, ~100% mortality), a keystone species (Pisaster ochraceus, ~10-70% mortality), and one of its competitors (Leptasterias sp., ~100% mortality). Their objectives during this first year following the natural large-scale die-off are to  quantify the abundance and distribution of the target species at sites across the impacted range and reference sites to the south and north,  develop and use genetic markers to identify the sources and dispersal distances of new recruits of P. ochraceus, Leptasterias sp., and S. purpuratus that recolonize the impacted range, and  describe changes in abundance of these three species and their prey and competitors at sites throughout the impacted range.