MEPS 322:303-309 (2006)  -  doi:10.3354/meps322303

An isotopic assessment of the feeding habits of free-ranging manatees

Kimberly J. Reich1,2,*, Graham A. J. Worthy1,3

1Physiological Ecology and Bioenergetics Lab, Department of Marine Biology, Texas A&M University at Galveston, 4700 Avenue U, Galveston, Texas 77551, USA
2Present address: Archie Carr Center for Sea Turtle Research, Department of Zoology, University of Florida, Box 118525, Gainesville, Florida 32611-8525, USA
3Present address: Physiological Ecology and Bioenergetics Lab, Department of Biology, University of Central Florida, 4000 Central Florida Blvd., Orlando, Florida 32816-2368, USA

ABSTRACT: There is relatively little information available on how the relative importance of fresh, brackish, or marine environments may vary geographically or individually with respect to manatee Trichechus manatus latirostris feeding ecology. As a first application of stable isotope analysis to determine diet composition of wild manatees, skin from 25 manatee carcasses and leaf tissue from 25 plant species were collected from 4 regions in Florida and analyzed for relative values of stable carbon (δ13C) and nitrogen (δ15N) isotopes. Values of δ13C and δ15N measured in plants ranged from –0.8 ± 1.0 to 6.4 ± 0.0‰ and in manatee tissues from –8.7 ± 0.2 to –28.3 ± 0.1‰, respectively. A mixing model was applied to estimate manatee diet composition across different geographic regions, and results (mean, all manatees, all regions) indicated that, overall, Florida manatees consumed 44% of their diet from marine and/or estuarine sources. Manatees living along the central east coast obtained 100% of their diet from marine and/or estuarine sources, while animals recovered from the St. John’s River system (NE region) obtained ~50% of their diet from freshwater sources, suggesting that some time had been spent outside of the river basin. In conclusion, results of the stable isotope analysis suggest that, even though manatees have a physiological requirement to ingest fresh water, marine and estuarine environments supply a significant fraction of their food resources.

KEY WORDS: Manatee · Isotope · Foraging · Aquatic plants · Seagrass

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