PS 13-133 - Spatial variation in trophic interactions of bottlenose dolphins in estuarine habitats of the Florida Coastal Everglades

Background/Question/Methods

Common bottlenose dolphins (Tursiops truncatus) are abundant upper trophic level predators found in a range of coastal habitats in the southeastern USA. In the Florida Coastal Everglades (FCE), they occur in the estuarine river system, adjacent bays, and in the coastal waters. Little is known on the trophic interactions of bottlenose dolphins in the FCE and how they might vary within and among habitats. This is particularly important since these predators have the potential to constitute trophic links between marine and freshwater habitats given their large body size, high metabolic rates, high abundance, and capacity for long-distance movement. We used stable carbon (δ13C) and nitrogen (δ15N) isotope analysis of dolphins, skin (n = 89) and blubber (n = 89) tissues, and potential prey, muscle tissue (n = 127), to investigate trophic interactions of dolphins across five major regions of FCE, including mesohaline rivers, an inland low-salinity bay, a coastal oligohaline bay, and marine waters of Florida Bay, and the Gulf of Mexico. We also investigated whether trophic interactions of dolphins varied with ages estimated using DNA methylation and sex.

Results/Conclusions

δ¹³C values of prey taxa varied spatially. Values of δ¹³C of dolphins indicated that, unlike other top predators studied in the FCE (bull sharks, Carcharhinus leucas; American alligators, Alligator mississippiensis), bottlenose dolphins forage consistently in food webs of the habitats where they were sampled. Values of δ¹⁵N, however, suggest that dolphins feed at a similar trophic level throughout the FCE. Neither δ¹⁵N nor δ¹³C varied significantly with estimated age or sex. Our results suggest that, despite their high mobility, bottlenose dolphins in FCE compartmentalize their feeding in the general habitats of which they are found and may play ecological roles that differ from other large-bodied predators in the system shown to link distinct food webs through foraging behaviors.