Diverse resource-use strategies in a large-bodied marine predator guild: Evidence from differential use of resource subsidies and intraspecific isotopic variation

Observations of resource-use dynamics are sparse for higher trophic level species in marine systems, but important given their role in driving the distribution and functional roles of species. For a guild comprised of 7 large-bodied shark species captured in Florida Bay, we used multi-tissue stable isotope analysis to evaluate the extent of resource-use diversity within and between 2 time periods. We examined: (1) variation in community-wide isotopic niche structure across time (i.e. Layman’s community metrics); (2) variation in species’ trophic position; (3) reliance upon dominant resource pools (inland mangroves vs. coastal neritic [i.e. seagrass and/or reef-associated prey]; and (4) patterns of intraspecific isotopic variation across species (i.e. standard ellipse area, ellipse eccentricity E, ellipse inclination θ, and total isotopic overlap). Community-wide isotopic niche characteristics varied with tissue type, suggesting temporal plasticity in community resource use. Our novel approach integrating multiple isotopic baselines resulted in consistently high trophic position estimates (> 5.0), but the utilization of available resource subsidies varied with species and tissue type. Whole blood suggested recent use of inland mangrove-derived prey resources, while fin tissue suggested differential use of both inland mangroves and coastal neritic-derived subsidies. Our results suggest that sharks display dynamic resource use in space and time, with limited functional complementarity across species. The adoption of diverse resource-use strategies, both within and among species, could facilitate the co-occurrence of large-bodied predator species and underscores the role of sharks as vectors of ecosystem connectivity.