Award: OCE-1031061

This project aimed to build a global collaborative team and network of field experiments to understand how two key stressors influence coastal seagrass ecosystems, excess plant nutrient runoff and changes in communities of beneficial grazers caused by fishing. The research focused on eelgrass (Zostera marina), a marine plant that supports fisheries and coastal protection but that is threatened worldwide, and on small invertebrates that may be essential partners in promoting eelgrass by feeding on the algae that can overgrow it. Despite their suspected importance in maintaining valuable marine vegetation, the beneficial role of these inconspicuous grazing animals had not previously been documented conclusively in the field. The project established an open, collaborative community of >30 researchers from five states (VA, NC, MA, CA, WA) and seven countries, ranging from senior scientists to undergraduates, called the Zostera Experimental Network (ZEN, www.zenscience.org). ZEN conducted coordinated experiments around the world in 2011 and 2012 testing how changing plant nutrients, grazing by small invertebrates, and changing biodiversity affect productivity and transfer of energy and carbon through the food web, and how these processes vary with climate and environmental factors. Intellectual merit ZEN achieved an important advance in resolving the long-debated question of what controls the abundance and distribution of valuable but threatened submerged vegetation. First, the experiments demonstrated that, across the global network of 15 sites, grazing by invertebrates (top-down control) had stronger and more consistent effects on biomass of algae than did fertilization by excess plant nutrients (bottom-up control). Second, the research provided new large-scale evidence that ecosystems with naturally high biodiversity tend to be more productive. Specifically, eelgrass meadows with more grazer species and higher genetic diversity of eelgrass showed stronger control of algae and higher production of invertebrates that provide forage for juvenile fishes. A surprising finding was that this variation in biodiversity had comparably strong influence on productivity as did major environmental factors like temperature and salinity. This finding is also important because it matches closely the results of prior experiments in simplified laboratory systems, and therefore supports earlier conclusions that diverse communities of small algae-eating invertebrates are key players in vegetated marine ecosystems and can facilitate dominance by seagrasses over algae. Broader impacts Results of this project have potential management implications because they suggest that human disturbance of marine fauna can significantly affect algal overgrowth and health of valuable submerged aquatic vegetation ecosystems. ZENÆs collaborative network approach also generated wide interest and excitement as a cost-effective, flexible model for other groups approaching big questions in marine and environmental science. The Principal Investigator (PI) and Project Coordinator were invited to several conferences and keynote speeches including panel discussions and symposia on research networks at the 2012 and 2015 Ecological Society of America meetings, and a keynote presentation at the World Conference on Biodiversity in China in 2014. ZEN directly inspired several similar efforts to build collaborative, experimental networks in other marine habitats including kelp forests, coral reefs, and tropical seagrass meadows. The results of ZEN research provide the most convincing evidence yet that changes in the food web can ripple down to affect the seagrasses at its base, implying that management and conservation of seagrass habitats will be improved by accounting for impacts of fishing and pollution that affect grazer populations. Last Modified: 04/13/2015 Submitted by: J. Emmett Duffy