Rates of Sediment Resuspension and Erosion Following Green Turtle Grazing in a Shallow Caribbean Thalassia testudinum Meadow

Seagrass meadows buffer sediments against resuspension and erosion by reducing water velocity and attenuating wave energy, thereby promoting accumulation of sediment and associated carbon. Grazing by green turtles (Chelonia mydas) can significantly reduce the aboveground canopy in meadows. Increasing green turtle population sizes will return more seagrass areas to a naturally grazed state; however, it is not well understood how green turtle grazing will affect sediment processes in seagrass meadows. To evaluate effects of grazing, we measured sediment erosion following a clipping experiment in a shallow Caribbean Thalassia testudinum seagrass meadow and rates of sediment resuspension in an area naturally grazed by turtles. Following removal of the seagrass canopy, erosion of surface sediments did not increase compared to unclipped reference plots during the clipping experiment. We provide the first estimates of particle deposition and resuspension rates from a seagrass meadow grazed by green turtles. Rates did not differ between areas naturally grazed for at least one year and ungrazed areas. On average, 51% of the total sediment flux was comprised of resuspended sediments in the area grazed by turtles, and 52% in the ungrazed area of the meadow. Green turtle grazing also did not affect the carbon content of sediment particles or the downward carbon flux in the meadow. Our results demonstrate that grazing did not increase the vulnerability of surface sediments to loss in this system, and as green turtles recover, their natural grazing regime may not directly affect sediment processes contributing to carbon accumulation in shallow, coastal meadows.