Dynamics and aging of green turtle grazing plots at two Caribbean seagrass meadows

Abstract

Concerns over the sustainability of green turtle grazing have become a central topic in discussions of seagrass protection. Understanding grazing plot dynamics and aging is critical to evaluating the sustainability of grazing and understanding the role green turtles play in structuring seagrass foraging habitats. We investigated grazing plot dynamics and aging at 2 naturally grazed seagrass meadows in the Caribbean: one experiencing increasing grazing and one experiencing decreasing grazing. By integrating in-water characterization of grazing plots with aerial imagery of naturally grazed meadows, we show that green turtle grazing plots are dynamic, with establishment of new plots, expansion and merging of existing plots, and abandonment and regrowth of plots occurring within 3 and 13 mo periods. We also document that green turtles contribute to a component of habitat complexity by increasing edge habitat in seagrass meadows, and that they can maintain grazing plots for more than 9 yr. By July 2019, green turtles had been maintaining grazing plots for at least 6.65 yr where grazed area was decreasing and for at least 9.22 yr where grazed area was increasing. We offer new insight into the life cycle of grazing plots and show that green turtle grazing plot use is sustainable over longer periods than previously documented. Future studies investigating grazing plot dynamics and evaluating the sustainability of green turtle grazing over longer periods, across seasons, and in different regions, as well as evaluating cumulative effects of anthropogenic stressors, will be key to effective co-management of green turtles and globally declining seagrasses.