Bjorndal, 1997:

"Sea turtles can have major effects on nutrient cycling and community structure in their foraging habitats.  Under natural conditions, the high population densities that sea turtles can attain make them major predators and grazers in their ecosystems.  Seagrass ecosystems, found in relatively shallow waters worldwide, are among the most productive in the world.¹²⁹  Grazing by green turtles has significant effects on the structure and nutrient cycling in these systems.  Green turtles establish and maintain grazing plots in pastures of the seagrass T. testudinum by continually recropping areas that they have earlier grazed and thus ingest a diet higher in protein and lower in lignin.⁴²  These plots vary in size from 10 to 100m² and can be maintained for over two years.¹³⁰  Green turtles increase the speed of nutrient recycling in Thalassia beds by shortening the time required for normal decomposition of Thalassia blades, perhaps as much as from eight weeks to a few days.⁴  Thalassia blades that are consumed by green turtles and deposited in feces have greatly reduced particle size and lower (= enriched) C to N ratio compared to blades that die and decompose in site.⁴  Continual cropping by green turtles can also stress Thalassia plants, resulting in lower blade productivity and reduced leaf width, rhizome diameter, and leaf-shoot density.^131-133  The stress may be caused by reduced nutrient availability, which may result from decreased trapping of detritus within the seagrass bed by blades that have been grazed to a few centimeters in height.⁵  Thus, grazing by green turtles can have both positive and negative effects on seagrass nutrition. Although never quantified, grazing on algae by green turtles on coral reefs must have significant effects on percent cover by algae in these ecosystems."

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Citation and/or URL

Bjorndal, K. A. 1997.  Foraging ecology and nutrition of sea turtles. Pp. 199-232. In: Lutz, P. L., and Musick, J. A. [Eds.]. The Biology of Sea Turtles. CRC Press. Boca Raton, New York, London, Tokyo. 432pp.  

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International 

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50 years 

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