Overview: This research will produce the second generation of a global collaborative research project, the Zostera Experimental Network (ZEN) to quantify the interacting influences of environmental forcing, biodiversity, and food-web perturbations on structure and functioning of eelgrass (Zostera marina) beds, the foundation of important but threatened coastal ecosystems worldwide. Partners at 40 sites in 14 countries will conduct parallel, standardized field sampling of producer and consumer biomass and diversity, and measure grazing and predation rates, to produce a global map of biodiversity, biomass distribution among trophic levels, and ecosystem processes in eelgrass habitats. Partners at a subset of core sites will conduct factorial experiments to characterize the interaction of nutrient loading, predator loss, and biogenic habitat structure (eelgrass density) in mediating producer growth and trophic processes in eelgrass. Finally, guided by the results from mechanistic experiments, the global field data will be used to test specific hypotheses about impacts of climate warming, nutrient loading, and declining biodiversity on eelgrass ecosystems via structural equation modeling, a uniquely powerful approach to dissecting complex interacting networks of causality. The proposed research will characterize in unprecedented detail how environmental forcing, biodiversity, and food-web processes interact to mediate functioning of a coastal ecosystem on a global scale. There are four general objectives:
1. Quantify linkages between eelgrass genetic diversity, growth, and provision of animal habitat 2. Quantify the influence of eelgrass habitat structure on consumer-prey interactions, secondary production, and trophic transfer 3. Identify mechanisms for the influence of grazer diversity on algal control 4. Develop a global map of grazing and predation intensity to assess the relative importance of bottom-up and top-down forcing in eelgrass beds
Intellectual Merit: This program's integrated characterization of biodiversity, ecosystem state variables, and process rates across the globe is arguably unique in any marine system. It builds on promising results from the first generation of ZEN to allow for the first time a rigorous analysis of links between biodiversity and ecosystem functioning in a natural system on a global scale. As part of this analysis, the proposed research will provide the most comprehensive analysis yet of the controversial question of the relative importance of bottom-up and top-down forcing in seagrass ecosystems, an issue of fundamental importance to management and conservation.
Broader Impacts: Seagrasses and the many ecosystem services they provide are declining worldwide. This project's data on higher trophic levels and food-web interactions will provide a valuable and overdue complement to the many monitoring programs around the world that focus primarily on seagrasses and water quality, and will ultimately be made available to parameterize and test models of threatened seagrass ecosystems at a higher level of resolution ecological reality than previously possible. The success of the Zostera Experimental Network (ZEN) is evidenced by the continuation of all but one partner in the second generation (ZEN 2), and recruitment of nearly the same number of new partners to this global collaboration. This research will solidify and expand this network by more than doubling the number of participating sites, collaborating with parallel European Union and Japanese efforts, and integrating the world's largest and most successful seagrass restoration project at the Virginia Coast LTER site. ZEN 2 will also provide intensive training and international research experiences for at least 15 undergraduate interns, several graduate students, and a Postdoctoral Scholar, advance an innovative model of comparative-experimental research in global marine ecology, and produce a comprehensive database and analytical framework that will be invaluable to global efforts at conservation and management of threatened seagrass systems.
