Using stable isotopes to investigate trophic interactions of bottlenose dolphins (Tursiops truncatus) in the Florida Coastal Everglades

Background/Question/Methods

Top predators can affect their communities through “top-down” effects including direct predation and inducing behavioral modifications (e.g. risk effects). Recent research suggests that they may also play “bottom-up” roles in ecosystems, including transporting materials within and across habitat boundaries. The Florida Coastal Everglades (FCE) is an “upside-down” oligotrophic estuary where productivity decreases from the mouth of the estuary to freshwater marshes. Therefore, movements of predators may be important in ecosystem dynamics.  While other estuarine predators in the FCE have been shown to potentially move nutrients among ecosystems, the potential for bottlenose dolphins (Tursiops truncatus) to play a similar role in the systems has not been investigated. Stable isotope analysis of biopsy samples were used to investigate spatial variation in trophic interactions of dolphins to see if they might transport nutrients. 

Results/Conclusions

Values of of δ¹⁵ N  suggest dolphins feed at a trophic level similar to other top predators in the ecosystem while δ¹³ C suggest that dolphins forage largely within food webs where they were sampled rather than transporting nutrients across ecosystem boundaries.  The exception may be dolphins foraging in rivers, which may transport nutrients downstream; a pattern opposite to that of bull sharks and alligators in these habitats. Further research is necessary to predict how future changes occurring due to restoration and climate will affect the ecological roles of dolphins.