Biodiversity and Complex Forcing of Ecosystem Functioning in the Marine Foundation Species, Eelgrass: A Global Experimental Network

College Of William & Mary Virginia Institute Of Marine Science, Gloucester Point VA

Investigators

Abstract

Intellectual Merit. This project will develop a global collaborative network of field experiments to quantify how resources and grazing interactively affect biomass, production, and trophic transfer along natural gradients in biodiversity and abiotic forcing. It focuses on a key mutualism between invertebrate mesograzers and the globally distributed eelgrass (Zostera marina), as a model system and as the foundation of important but threatened coastal ecosystems worldwide. This interaction provided a model for influential experiments linking biodiversity to functioning (BEF) of multitrophic ecosystems. Yet, seagrass ecology has historically focused almost exclusively on bottom-up forcing, and impacts of these ubiquitous animals in the field are nearly unknown.The research program will address three questions: (1) What role do crustacean mesograzers, the benthic equivalents of grazing copepods, play in regulating vegetated coastal ecosystem functioning and buffering effects of eutrophication? (2) Are generalizations derived from 15 years of BEF experiments consistent with variation in ecosystem properties along natural diversity gradients in complex, open marine systems? (3) Do relative influences and interactions of resource supply, grazing pressure, and biodiversity on ecological processes vary systematically with climate and abiotic environmental drivers? Methods will include two novel approaches. First, a new technique that excludes crustacean mesograzers without cage artifacts will rigorously test their long-suspected role in fostering macrophyte dominance. The project assembles experienced collaborators who will conduct identical factorial experiments manipulating grazers and nutrient loading at each of 12 sites spanning the sub-global range of eelgrass, across concomitant gradients in diversity and abiotic forcing variables. Second, Structural Equation Models (SEM), designed specifically to quantify relative importance and interactions among variables in complex systems, will tease apart effects of resource supply, grazer biomass, species composition, and richness, and several abiotic variables on eelgrass and algal biomass, production, and trophic transfer. Small-scale experiments with synthesized communities show that biodiversity generally enhances production and resource use in a range of ecosystems, but the importance of diversity relative to other well-documented forcing factors remains poorly understood. Intriguingly, BEF relationships in the few studies from wild ecosystems often saturate at much higher richness than in experiments, suggesting that prior work may underestimate rather than overestimate functional effects of diversity. Yet few large-scale data sets are available to evaluate this conjecture. This research will do so on a global scale in eelgrass beds, one of the few community types in which such a test is possible. Broader Impacts. This project will initiate a lasting, and open, collaborative network of researchers studying the functioning of multitrophic marine vegetation ecosystems. It leverages a wealth of globally distributed collaborator expertise, person power, and experience with multinational partnerships including a new network of marine plant-herbivore ecologists funded by the Australian Research Council; the Census of Marine Life's NaGISA project; and key partners in MarBEF's BIOFUSE project. It will thus catalyze integration of several formerly independent research efforts. The project will also help establish the next generation of collaborative marine vegetation ecologists through a student exchange program: students from each partner site will participate fully in the experiment at one of the other sites, providing field experience in new systems, and fostering relationships with new colleagues lasting well beyond the tenure of this award. Students will be recruited from the existing Hall- Bonner Program for Minority Doctoral Scholars in Ocean Sciences, of which VIMS is a partner, and from several other local programs that train underrepresented groups in marine science.