Foundation species, such as corals, kelp, and conifer trees, are dominant, structure-forming organisms that are often the focus of management because they exert powerful control over all other plants and animals in the ecosystem and the regulation of ecosystem services. Secondary foundation species are dependent on foundation species and by further affecting biodiversity and the microclimate can help maintain biological productivity, chemical balances, and other ecosystem functions at higher levels than those maintained by foundation species alone. Theory predicts that ecosystems that support high biodiversity and functioning, like those structured by foundation and secondary foundation species, should be especially resilient to environmental stresses, like droughts, heat spells and disease outbreaks, that might otherwise drive ecosystems to collapse. This project uses salt marshes on the Georgia coast as a model ecosystem to test these theories. These marshes are structured by a foundation species, cordgrass, with clusters of ribbed mussels as secondary foundation species. An experiment in actual marshes will be conducted to help determine whether an overlap of mussels within cordgrass increases resistance to or recovery from drought and grazing by snails, two stresses that have acted together to kill more than 250,000 acres of cordgrass here over the last twenty years. One PhD student from the University of Florida will participate in this project along with two undergraduate students. Outreach will be through participation of the investigator in an after-school summer program for K-5 girls, a spring-break program for 7-8th grade girls, and a public school science teachers program. The results will also be used for designing new approaches to managing and conserving ecosystems that optimize the benefits of multiple foundation species.
Over 18 months, the researchers will use rain and tide exclusion structures and snail inclusion cages to manipulate drought and snail grazing in plots that contain aggregations of 0, 40 or 80 mussels to test their hypothesis that the level of resistance and rate of recovery of eight, distinct ecosystem functions and two indices of salt marsh multifunctionality to these stressors increase with increasing numbers of mussels. In addition, they will measure five of the same ecosystem functions in aggregations that vary in size at sites distributed from Florida to North Carolina to investigate if mussels enhance salt marsh resilience to natural fluctuations in environmental stress across this region. In analyzing changes in invertebrate communities, soil conditions, grazing intensity, and ecosystem functions over time, this project will expose the ecological and biogeochemical mechanisms by which this secondary foundation species may mediate resilience and to identify whether larger aggregations provide more protection against these stressors than smaller aggregations within salt marsh landscapes. As a result, this experiment and survey will produce information critical to evaluating if hierarchical interactions among foundation and secondary foundation species should be incorporated in our conceptual understanding of forces that regulate biodiversity, ecosystem functioning, and resilience.
