Role of environmental and biodiversity gradients in bottom-up and top-down control of seagrass communities: A collaborative field experiment across the Northern Hemisphere

Richardson, John Paul

Tuesday, August 7, 2012: 10:50 AM

D139, Oregon Convention Center

Pamela L. Reynolds, Department of Environmental Science and Policy, University of California, Davis, CA, J. Emmett Duffy, Tennenbaum Marine Observatory Network, Smithsonian Institution, Washington, DC, Christoffer Böstrom, Åbo Akademi University, Åbo, Finland, James Coyer, Department of Marine Benthic Ecology and Evolution, University of Groningen, Mathieu Cusson, Aquatic science laboratory, Université du Québec à Chicoutimi, Quebec, QC, Canada, Masakazu Hori, Fisheries Research Agency, Japan, James G. Douglass, Marine Science Center, Northeastern University, Nahant, MA, Kevin A. Hovel, Coastal and Marine Institute Laboratory and Department of Biology, San Diego State University, San Diego, CA, Johan Eklöf, Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg, Sweden, Aschwin Engelen, Centre of Marine Sciences (CCMAR), Faro, Portugal, Britas Klemens Eriksson, Benthic Ecology, University of Groningen, Netherlands, Stein Fredriksen, University of Oslo, Norway, Lars Gamfeldt, Department of Biological & Environmental Sciences, University of Gothenburg, Gothenburg, Sweden, Katrin Iken, University of Alaska Fairbanks, AK, Per-Olav Moksnes, Department of biological and environmental sciences, University of Gothenburg, Gothenburg, Sweden, Masahiro Nakaoka, Hokkaido University, Japan, Mary O'Connor, Zoology, University of British Columbia, Vancouver, BC, Canada, Jeanine Olsen, Marine Benthic Ecology & Evolution (MarBEE), University of Groningen, Groningen, Netherlands, John Paul Richardson, School of Marine Science & Virginia Institute of Marine Science, The College of William and Mary, Gloucester Point, VA, Jennifer L. Ruesink, Department of Biology, University of Washington, Seattle, WA, Erik E. Sotka, Department of Biology and Grice Marine Laboratory, College of Charleston, Charleston, SC, John J. Stachowicz, Department of Evolution and Ecology, University of California, Davis, Davis, CA and Jonas Thormar, University of Oslo, Oslo, Norway

Background/Question/Methods

Two fundamental, and related, challenges to prediction in ecology are complexity and idiosyncrasy. How do we evaluate the importance of multiple, interacting factors in mediating ecological structure and processes? And how do we assess whether the results are general? One promising way forward is the comparative-experimental approach, which integrates standardized experiments with observational data across environmental gradients to evaluate interactions among multiple processes and to test their generality. In the summer of 2011 the Zostera Experimental

Network (ZEN), a collaboration among ecologists across 15 Northern Hemisphere sites, initiated a set of parallel field experiments to explore the influence of regional gradients in biodiversity and environmental forcing on the balance of bottom-up and top-down control in communities of eelgrass (Zostera marina), a marine foundation species. Eelgrass is among the most widespread and abundant marine plants, and forms ecologically and economically important but threatened coastal habitats throughout the Northern Hemisphere. We factorially added nutrients and excluded small crustacean grazers (mesograzers) using a degradable chemical deterrent for 4 weeks at each site, and measured responses of the plant and associated animal communities.

Results/Conclusions

As expected, results varied strongly across the global range. Our cage-free deterrent treatment strongly reduced crustacean grazers everywhere, and at several sites this grazer exclusion released blooms of epiphytic algae and/or sessile invertebrates, which fouled the eelgrass leaves. In Chesapeake Bay, USA, where the experiment ran eight weeks, these algal blooms strongly reduced eelgrass biomass, demonstrating a mutualistic dependence between eelgrass and mesograzers. Surprisingly, given the prominent emphasis on eutrophication in seagrass ecology, nutrient addition generally had little effect on epiphyte accumulation or eelgrass growth. Ongoing research is analyzing the relative influence and interactions of grazer diversity and environmental forcing in mediating the variance in regulating processes across the global range.

COS 36-9 - Role of environmental and biodiversity gradients in bottom-up and top-down control of seagrass communities: A collaborative field experiment across the Northern Hemisphere