Simulated green turtle grazing affects nutrient composition of the seagrass <Emphasis Type="Italic">Thalassia testudinum</Emphasis> |
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Authors: | Kathleen L Moran Karen A Bjorndal |
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Institution: | (1) Archie Carr Center for Sea Turtle Research and Department of Zoology, University of Florida, P.O. Box 118525, Gainesville, FL 32611, USA |
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Abstract: | Before populations of green turtles (Chelonia mydas) were severely reduced by human overexploitation, the seagrass Thalassia testudinum was intensively grazed by green turtles in the Caribbean. To explore how nutrient composition of T. testudinum pastures responds to intense grazing pressure, we simulated green turtle grazing in 15 plots (each 3 m × 3 m) for 16 months
in the central Bahamas. Comparisons of clipped plots with 15 adjacent control (unclipped) plots revealed that simulated grazing
resulted in significantly higher energy, nitrogen, phosphorus, lignin, cutin, and condensed tannin content in blades in clipped
plots, but sediment organic content was not affected. By continually re-cropping blades in grazing plots, turtles ingest young,
actively growing blade tissue with higher energy, nitrogen, and phosphorus concentrations. Our 16-month clipping trial did
not generate the expected decline in nutrient content in T. testudinum blades under intensive grazing. However, significant decreases in nitrogen and organic matter reserves in rhizomes, with
declines apparent after 16 and 11 months, respectively, indicate that nutrient content of blades and/or blade productivity
may decline under continued clipping. |
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