Green turtles (Chelonia mydas), who primarily graze on seagrass, have the potential to affect seagrass communities; thereby understanding the effect of predator presence on grazing behavior is important. Many regions are implementing sea turtle and even shark protection, but many marine ecosystems within these regions are strongly affected by human generated stressors. In Abaco, Bahamas, the lab has a rare opportunity to study the non-human factors affecting a recently protected green turtle population so that management agencies can apply ecologically meaningful conservation tactics.
Using unmanned aerial video (UAV), baited remote underwater video (BRUV), and seagrass surveys the lab studies green turtle foraging ecology including how food availability, food nutritional quality and predation risk affect turtle habitat use and the impact of turtle grazing on seagrass communities. This is the first explicit test of whether Caribbean green turtle distributions reflect a trade-off between risk and energy intake or if foraging considerations alone determine spatial variation in turtle densities. The lab is also studying the effects of green turtle grazing on seagrass communities using a multi-year grazer exclusion study within four tidal creek sites along Abaco’s eastern coastline.
In 2014, the Heithaus Lab expanded their study of Caribbean sea turtles to Guadeloupe, Martinique and St. Martin where Halophila stipulacea, a seagrass native to the Indian Ocean, has successfully spread. Likely transported by pleasure yachts from the Mediterranean, H. stipulacea is fast-growing, a high-volume seed producer, and can tolerate a wide range of salinities, temperatures, depths, and disturbance regimes. Here, researchers in Mike’s lab study the potentially important role grazers can play in mediating the effects of invasive plant species by either increasing the rate of invasion by preferentially grazing on native seagrasses or by decreasing the rate of invasion by preferentially grazing on the invasive seagrass.
To do so, the lab surveys turtle densities on snorkel, conduct focal follows of green turtles to observe foraging behavior and activity budgets, survey seagrass communities to map food availability and collect samples of foraging options to assess links between grazing preferences and food quality. With the assistance of the lab’s collaborators, the Heithaus team also deploys turtle-borne cameras, GPS tags and satellite tags to track turtle movement patterns; capture turtles to collect size and weight data to assess growth and condition; and collect biopsy samples for more in-depth diet studies. Through these studies the team will elucidate the role of green turtles in a non-native seagrass invasion.