Green turtles in the Caribbean feed selectively on the seagrass Thalassia testudinum; however, they do not graze at random. Rather, they maintain “grazing plots” of young blades of T. testudinum by consistently recropping them. By routinely cropping these plots, they’re increasing their protein intake while keeping lignin consumption low, essentially making their food more digestible. This grazing pattern also increases nitrogen content over time, yielding a higher nutrient diet. Lignin is a complex organic polymer deposited in the cell walls of many plants, making them rigid and woody. Also, lignin has been repeatedly identified as the major chemical component controlling the digestibility of cell walls; therefore making it more difficult to break down. In ungrazed blades of T. testudinum, lignin levels are 100% greater than in blades from grazed strands. When establishing a new grazing plot, green turtles will bite at the base of the tall T. testudinum blades and allow the upper, older portions that are high in lignin and covered in epiphytes to float away. Thus, the digestive efficiencies of green turtles and forage quality are enhanced by their specialized feeding behavior.
We have been placing stationary cameras in established grazing plots and have witnessed this maintenance behavior. I am excited to see what other behaviors we’ll be able to observe.