Developing a Regional Context for Rocky Subtidal Communities: Upwelling, Biotic Interactions and Diversity Regulation in the Galapagos Marine Reserve

Brown University, Providence RI

Investigators

Abstract

The foundation of community ecology has been constructed from studies conducted on relatively small spatial scales. In marine ecology, the building blocks of the foundation are analyses of species interactions at focal sites that are bathed by currents transporting nutrients, food and reproductive propagules of the next generation of organisms. Thus, the communities living at local sites are linked to some extent on larger spatial scales by oceanographic processes. Understanding the extent and scale of such linkages is essential for the growth of community ecology as an intellectual endeavor and also for predicting how local biota of coastal marine ecosystems will be modified by an increasing pace of global change. The latter situation applies because global atmospheric processes regulate the oceanic currents that couple local sites. Although the need to expand the spatial scale of marine research has been recognized for nearly two decades, progress in developing a regional oceanographic perspective in marine benthic ecology has been slow, particularly for sub-tidal ecosystems. This project herein relates to these broader goals by developing a regional context for benthic communities living on steep underwater sides of islands (rock walls) in the Galapagos Marine Reserve, (GMR) the second largest marine protected area in the world (Bustamente et al 2000). Due to nutritive upwelling currents and marine food webs that are nearly intact, GMR subtidal ecosystems provide an excellent opportunity to investigate the importance of bottom ?up (i.e. driven by food resources) vs top?down (predatory) regulation of benthic communities. Preliminary research by the project team indicates that the pace of community change is especially rapid where currents flow up rock walls at some of highest upwelling velocities reported (to 60 cm s) to date. An experimental design is used to test the general hypothesis that bottom? up and top ?down control of rock wall communities varies predictably as a function of upwelling. Regular measurement of upwelling currents, chlorophyll a, nutrient and zooplankton concentrations at 8 sites in the central GMR will be placed in a larger context by comparison to daily, high resolution images of chl a provided by the new SeaWIFS facility at the Charles Darwin Research Station. Measuring algal accumulation in treatments protected from and exposed to grazers will assess a response of benthic algae to the potentially enhanced upwelling nutrient regime. Because epifaunal. invertebrates feeding on plankton link water column production to higher trophic levels,, experiments are proposed to measure the growth and recruitment of 5 epifaunal species and their consumers (snails, sea urchins) to test the predictions of bottomup and top?down linkage . Key predators will be enclosed to evaluate the hypothesis that the strength of species interactions is greatest at upwelling sites while video cameras will provide another measure of site variation in consumer pressure. Finally, theory and observation suggest that the highest diversity and turnover of diversity occurs at upwelling sites due to rapid invertebrate production and high predation on primary space occupiers. By working at the crossroads of community ecology, oceanography and conservation biology, the research will increase our understanding of how productivity and local variation in species interactions influence species diversity in marine reserves. The broader merits of the proposal are that it will directly contribute to conservation planning, train a PhD student and positively impact undergraduate and graduate teaching.