The impact of turtle grazing on the resilience of seagrass


This project will start in November of 2018 in a new and exciting collaboration with Ph.D. student Fee Smulders and professor Marjolijn Christianen from the Aquatic Ecology Group at Wageningen University in The Netherlands. This project will investigate the role of green turtle (Chelonia mydas) grazing on the resilience and ecosystem services of Caribbean seagrasses. 2018. Seagrasses act as bioengineers, constructing their own environment to form ecosystems that provide services, critical in a greater ecosystem context, including carbon sequestration, coastal stability, and the provision of habitat and refuge for a range of ecologically and economically important species, such as queen conch, spiny lobster and other species important to artisanal fisheries throughout the region.   


One of the greatest threats to these ecosystems is human induced disturbance, such as the urbanisaiton and development of coastal and nearshore environments, that can degrade or modify these habitats. Historically, the over-harvesting of macro-herbivores is also contributing to deleterious effects among many of these meadows throughout the Caribbean, including parrot fish and turtles. Large vertebrates have a big influence – either direct or indirect – on the functioning of seagrasses, for example moderate grazing by turtles can increase plant productivity, but overgrazing can lead to collapses of these meadows. In extreme cases, complete loss of seagrass can occur, exacerbating the recovery of these systems. However, the regulation of these herbivores by apex predators, such as sharks can influence the overall health of seagrasses, and this is particularly relevant in The Bahamas, where sharks are afforded absolute protection, resulting in their abundance. The absence of sharks and other predators, is likely to induce significant alterations in ecosystem function, and the subsequent services that seagrass ecosystems provide.


Here we will experimentally exclude turtles using ‘exclosure’ cages to investigate the role of turtle grazing in service and resilience. In Eleuthera, turtle grazing pressure and shark abundance is high, and so we will use a comparative site on the island of Bonaire in the Dutch Caribbean where sharks are largely absent. We hope to improve our understanding of marine plant-herbivore interaction, and quantify indicators of ecosystem resilience in order to provide much needed data to aid conservation efforts thought the region.


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