Science in the seagrass
WiSE Member Spotlight: Savanna Barry – PhD candidate, Fisheries and Aquatic Sciences
Seagrass meadows provide several irreplaceable functions, including reducing erosion of shorelines, improving water clarity, and providing extensive habitat for a diverse array of species. It has been estimated that ~85% of the fish species that support Florida’s recreational and commercial fisheries depend on seagrasses for at least part of their life cycle. Globally, seagrasses are often threatened by nutrient over-enrichment, chemical pollution, overfishing, dredging, and shoreline development. Nutrient over-enrichment is the most widespread threat to seagrasses and occurs when rainwater runoff from cities and farms delivers unnaturally high amounts of nitrogen and phosphorus (essential plant nutrients) to coastal waters. The high nutrients favor fast-growing algae, which can bloom and smother seagrasses by preventing light from reaching the bottom—a case of “too much of a good thing”. Improved management of nutrient over-enrichment and other threats is necessary if we want to protect seagrasses and the valuable functions they provide.
For several years, our lab group has collected data on water quality (nutrient levels, light penetration, pH, dissolved oxygen, salinity, temperature, and phytoplankton levels) and seagrasses off the central Gulf coast of Florida. Analysis of the historical data showed remarkable differences in the morphology (size and shape) of seagrasses along a gradient of phosphorus availability, with seagrasses in nutrient-enriched systems having larger leaves and taller shoots. You can see from the photograph that full-grown plants of the same species can vary widely in their height and biomass; this ability to vary morphology is called phenotypic plasticity. The extreme phenotypic plasticity of many seagrass species is thought to be an adaptation to survival in the highly dynamic coastal zones they inhabit.
I study how morphological variation is related to nutrient enrichment and how it affects seagrass resilience and the important functions provided by seagrasses. Adding shade screens over plots of seagrass simulates the light-blocking algae blooms that can occur when nutrients are over-enriched in an estuary. Last summer, I assessed the response of seagrasses with different morphology to shading in a controlled experiment where seagrasses were shaded for 5-weeks and then given full light for a 3-week recovery period. The dramatic differences in the morphology of seagrass shoots suggest seagrasses growing in waters with different nutrient levels may provide fundamentally different habitat for fish and invertebrates. I collected samples that will be used to determine the differences, if any, in the invertebrate communities inhabiting seagrass meadows with different shoot morphology.
Once the data are compiled, the results will help me draw conclusions about the resilience of seagrasses with different morphology. My research could help improve management of seagrasses by highlighting which types of shoots are most vulnerable to shading and determine how invertebrate communities are affected by structural differences in seagrass habitat. This kind of information is essential to setting water quality targets, choosing the best area for new aquatic preserves, or assessing the general health of a seagrass meadow during restoration efforts.
Check out “Seagrass Savanna“, a mini-documentary featuring Savanna’s research!
More about Savanna
Savanna grew up on a small farm in central Virginia and discovered her interest in marine ecology during family vacations to small fishing towns along the Chesapeake Bay. After earning her B.S. in Biology from the University of Virginia, Savanna split her time between Gainesville, FL and Little Cayman Island to earn her M.S. in Fisheries and Aquatic Sciences through the University of Florida. While in Little Cayman, Savanna completed her Divemaster certification and co-organized an island-wide effort to remove invasive lionfish from local coral reefs. After competing her M.S., Savanna moved back to Gainesville full-time to continue into a Ph.D. program at UF and plans to graduate in 2016.