Marine mammals feed at a variety of trophic levels and occur from freshwater to open-ocean ecosystems of all latitudes. Due to their abundance, large-scale movements, and high metabolic rates, they have the potential to affect the structure and function of ecosystems. Bottlenose dolphins (Tursiops truncatus) are an upper trophic level predator of the Florida Coastal Everglades (FCE), which is comprised of multiple habitats including creeks, rivers, shallow inland bays that feature numerous mangrove islands, and coastal oceans of the Gulf of Mexico and Florida Bay. As an abundant predator throughout the FCE, bottlenose dolphins could play important roles in the ecosystem through both top-down and bottom-up pathways. To date, however, little is known about trophic interactions of dolphins in the FCE and how they might vary within and among habitats. Stable carbon (δ13C) and nitrogen (δ15 N) isotope analysis of skin and blubber biopsy samples (n=50) were used to investigate trophic interactions of dolphins in four major habitats of the FCE. These habitats, including the Shark River estuary (freshwater/brackish, n= 8), Whitewater bay and Joe River (brackish, n= 17 and n=9, respectively), and Florida Bay (marine, n= 16), have food webs that are isotopically distinct.
Values of δ15N suggest that dolphins feed at a similar trophic level system-wide. Unlike other top predators in the ecosystem, however, δ13C values suggest that bottlenose dolphins appear to restrict their foraging within the habitats where they were sampled. Therefore, individuals may play important roles within the habitats where they are foraging but are unlikely to play a role transporting nutrients into more oligotrophic upstream waters.