Seagrass meadows fringe many temperate and tropical coasts and provide a range of ecosystem services, such as sediment stabilization, nutrient recycling, carbon sequestration, and acting as a habitat and/or nursery ground for numerous marine species, including economically important fish. Seagrass meadows are in decline worldwide as a consequence of eutrophication and pollution, physical destruction (e.g., dredging, coastal development, boat moorings), and global warming. In Bermuda the decline of seagrass meadows substantially exceeds the global rate of decline despite their protected status (picture 3.1 in slideshow above), and the main reason for their decline is likely increased grazing pressure by green turtles (picture 3.2), which increased in population size due to effective conservation efforts, a decline in their main predators (tiger sharks) throughout the Northern Atlantic and an increase of sea surface temperatures (favorable for tropical turtles). At the same time, Bermuda’s tropical seagrass species thrive under marginal subtropical conditions (low light and temperature in winter) and therefore have a low capacity to support the increasing population of grazing green turtles.
Together with the Department of Environment and Natural Resources of the Bermuda Gov. (DENR; Dr. Sarah Manual), Sawall joint a NSF-funded project (2017-2020; PI J Campbell, Smithsonian Institute) that investigates the interacting effects of grazing and nutrients on seagrass (Thalassia testudinum) along a latitudinal gradient of light and temperature in order to understand how climate change-driven shifts in species ranges (i.e. grazers) may affect seagrass habitats (picture 3.3). The so-called Thalassia Experimental Network (TEN) spans across 23 latitudes, with Panama being closest to the equator (9°) and Bermuda being the furthest north (32°). Data analysis is ongoing.
Students involved in the NSF seagrass project:
- Khalil Smith (B.Sc. University of Coastal Georgia, GA, USA, 2018-19)
The MABEE lab, together with Sarah Manuel, is currently seeking additional support to investigate and define seagrass management strategies that mitigates further seagrass decline and promotes seagrass recovery.