Biodiversity, trophic structure, and the stability of seagrass ecosystems. Of the many consequences of declining global biodiversity, impacts on the stability of ecosystem structure and functioning have generated some of the strongest interest. The last decade has seen renewed attention to the long-debated effects of biodiversity on stability, and several influential experiments in grassland plant assemblages and laboratory microbial microcosms support a link between them. These results, if general, are of clear importance in the face of accelerating loss and homogenization of biodiversity worldwide. Yet proposed links between biodiversity and stability remain poorly understood in natural, multi-level food webs. This research project will use eelgrass (Zostera marina) beds as a model system to test general hypotheses linking ecosystem stability with biodiversity and food web structure. By focusing on anthropogenic perturbations common to coastal ecosystems worldwide-eutrophication, overfishing, and exotic invasion-proposed experiments will also test rigorously the widely assumed dominance of bottom-up stressors (eutrophication) in comparison with the impacts of top-down stressors, and their interactions, in the ongoing global decline of seagrass ecosystems. Previous research has demonstrated important effects of biodiversity and trophic interactions on key properties of eelgrass ecosystems. This project will extend this research to more complete food webs, a wider range of anthropogenic perturbations, and interpretation of patterns in unmanipulated field systems. The goal is a comprehensive, mechanistic evaluation of linkages among biodiversity, food-web structure, and stability in a marine ecosystem of strong significance to humans. Such an integration previously has been attempted only for a few soil microfaunal and laboratory microbial communities. Specific objectives include: (1) Test experimentally the main and interactive effects of within-trophic level biodiversity, and foodweb structure (number and composition of trophic levels, and interaction strengths among them), on eelgrass ecosystem structure, functioning, and stability. (2) Test experimentally the roles of consumer diversity and food-web structure in buffering seagrass ecosystems against effects of anthropogenic eutrophication, predator removal, and invasion. (3) Test the ability of experimentally derived conclusions to predict structure and dynamics of unmanipulated seagrass ecosystems in nature. This project will use a complementary suite of mesocosm experiments, field experiments, and application of experimental results to predict and interpret patterns in unmanipulated field systems. Measured ecosystem response variables will include benthic biomass, community composition and diversity, macrophyte dominance, primary and secondary production, and trophic transfer. This project has two principal broader impacts. First, the general focus on ecological stability is of substantial practical importance because human societies depend strongly on reliability of ecosystem services such as water purification and fisheries production. More specifically, seagrass beds are economically important ecosystems worldwide, but are declining for reasons widely attributed to anthropogenic eutrophication. This project will test experimentally the relative importance of eutrophication and food-web changes in this decline. Second, the project will train several students, from high school through Ph.D. levels, in experimental research on current issues at the dynamic interface of basic and applied marine ecology. Finally, it will coordinate with several recently initiated research projects addressing links between biodiversity and marine ecosystem functioning, contributing to an effort toward synthesis of this field.
(edited 15 Jan 04, J. Pawlik)
