EFFECTS OF GRAZING ON SEAGRASS MEADOW STRUCTURE AND FUNCTION
Seagrass meadows provide many valuable ecosystem services such as carbon sequestration, shoreline stabilization, and nursery habitat for many species. They also serve as a source of forage for grazers such as the green sea turtle (Chelonia mydas), a marine megaherbivore. Green turtles have a distinct grazing strategy — they create discrete grazing areas within meadows by cropping seagrass leaves to a short height and then re-grazing these same patches repeatedly. The creation and maintenance of these grazing patches modifies the physical structure of a seagrass meadow (for example, as seen in this photo of a grazing area (RHS of photo) in the Turks and Caicos Islands), and this habitat modification can then affect ecosystem functions in these areas (such as the production of organic matter supporting the local food web).
Green turtle abundance is increasing in many areas (a result of successful management and conservation efforts), which will lead to an increase in grazing within seagrass habitats (as more turtles will be in need of areas to graze). Given the many valuable services provided by seagrasses, an understanding of how these coastal habitats will respond to increases in large herbivore numbers will be critical for effective long-term management of these ecosystems. Through my research, I focus on understanding how green turtle grazing, through modification of the seagrass canopy, drives ecosystem structure and function in these important marine habitats.
GREENHOUSE GAS DYNAMICS IN HIGH-NUTRIENT FRESHWATER SYSTEMS
High nutrient concentrations stimulate organic matter production in lakes, which supports the food web and modifies greenhouse gas flux. Alterations to both nutrient availability and food web structure (e.g. through a change in predator density) can affect primary producer biomass dynamics, which in turn affects decomposition and thus greenhouse gas production. While the flux of greenhouse gases (i.e., carbon dioxide, methane, nitrous oxide) has received considerable attention in freshwater ecosystems in recent years, less is known about how food webs may drive changes in greenhouse gas flux, especially in high-nutrient systems.
With the myriad of threats facing lake ecosystems (e.g., species invasions, harmful algal blooms) lake food webs are subject to substantial modification which could be influencing greenhouse gas fluxes. My research aims to better understand how food web structure mediates these fluxes in nutrient-rich waterbodies.