Considerable research and debate has focused on the relationship between species diversity and ecosystem function. In contrast, few data are available to assess the impact of within species genotypic diversity on individual interactions, population processes, and ecological functions. Many marine benthic and planktonic communities are dominated by a single species: Macrocystis in kelp forests, Zostera in temperate seagrass beds, and Prochlorococcus in oligotrophic open ocean systems. Genetic diversity within these species may play an analogous role to species diversity in other systems, but few data are available that link functional differentiation of genotypes with their effect on community and ecosystem-level processes. The PIs' preliminary work suggests that clonal diversity in the eelgrass (Zostera marina), enhances resistance disturbance by grazing geese but the mechanisms underlying this effect and the importance of the effect under a range of disturbance types and intensities are unknown. Zostera plays a key role as the only macrophyte species in many temperate shallowwater communities worldwide, where it provides a critical ecosystem role, in terms of primary production, nutrient cycling, sediment stabilization, and provision of habitat for associated animal species. This system provides an opportunity to assess the effects of genotypic diversity on not only individual and population processes but also on community and ecosystem processes such as primary productivity and the abundance and diversity of associated animals. The PIs will conduct a series of laboratory, mesocosm, and field experiments to investigate the functional (ecological) consequences of genetic variation in Z. marina and how this variation contributes to the relationship between genetic diversity and ecosystem processes. Specifically, they will: (1) Quantify clonal variation in key physiological parameters such as photosynthetic rate, nutrient uptake and short term growth, (2) Investigate inter-shoot interactions between clonemates and non-clonemates and their impacts on overall eelgrass production under disturbed and undisturbed conditions, (3) Examine the inter-relationship between eelgrass genotypic diversity and disturbance on shoot density, seedling recruitment, and the associated community of seagrass epibionts in a factorial field experiment, and (4) Quantify changes in genotypic diversity over time in the presence and absence of disturbance in natural populations and the consequences of these changes for the rest of the ecosystem. Given the widespread decline of eelgrass and other key foundation species in marine systems, it is critical to understand the consequences of individual variation for population and community processes. Indeed, human activities are causing declines in genetic diversity in seagrasses at the scale at which ecosystem processes are measured and this research will provide much-needed information for federally mandated restoration efforts. Finally, this project will develop future scientists including a postdoctoral, and also graduate student and undergraduate researchers, including members from underrepresented groups.
