Abstract
Mobile, apex predators are commonly assumed to stabilize food webs through trophic coupling across spatially distinct habitats. The assumption that trophic coupling is common remains largely untested, despite evidence that individual behaviors of these predators might limit trophic coupling. We used stable isotope data from common bottlenose dolphins across the northern and eastern Gulf of Mexico to determine if these apex predators coupled estuarine and adjacent, nearshore marine habitats. 13C values differed among the sites, likely driven by environmental factors that varied at each site, such as freshwater input and seagrass cover. Within most sites, 13C values differed such that dolphins sampled inside and in the upper reaches of embayments had values indicative of estuarine habitats while those sampled outside or in lower reaches of embayments had values indicative of marine habitats. 15N values were more similar among and within sites than 13C values. Data from multiple tissues within individuals corroborated that most dolphins consistently used a narrow range of habitats but fed at similar trophic levels in estuarine and marine habitats. Individual habitat specialization in these dolphins maintained trophic compartments between estuarine and adjacent marine habitats at a regional scale, challenging the notion that trophic coupling by mobile, apex predators is widespread and common.
