Trophic Relationships and Niche Partitioning of Red Drum Sciaenops ocellatus and Common Snook Centropomus undecimalis in Coastal Estuaries of South Florida Christopher Malinowski 1,2 & Julie Cavin 3 & Jeffrey Chanton 4 & Lia Chasar 5 & Felicia Coleman 1 & Christopher Koenig 1 Received: 9 April 2018 /Revised: 27 November 2018 /Accepted: 12 December 2018 # Coastal and Estuarine Research Federation 2019 Abstract Large marine predators occupying the same spatial arena exhibit a variety of temporal and behavioral differences to minimize competition for habitat and prey. Here, we examined two such species in the Florida Everglades, red drum Sciaenops ocellatus and snook Centropomus undecimalis, to evaluate niche separation based on diet and multiple stable isotope (white muscle, δ 13 C, δ 15 N, δ 34 S) analyses. For these two estuarine predators, our results indicated that although dietary niche overlap was broad, different feeding modes (spatial and behavioral) allow niche partitioning. The diet of red drum was dominated by pink shrimp Farfantepenaeus duorarum and other demersal species. For snook, although their diet included significant numbers of pink shrimp, it was largely dominated by pelagic and epibenthic fishes. Mean red drum δ 13 C signatures (- 10.5 to - 20.8‰) differed significantly between areas and were strongly correlated with both area-specific seagrass concentration and amount of incidental seagrass ingestion. Mean snook δ 13 C signatures were generally depleted (- 20.9 to - 22.4‰) with the exception of one area (- 14.1‰). Red drum and snook diet and mean δ 15 N signatures (10.1‰, 10.8‰, respectively) indicated they were both mid-trophic-level consumers. Mean red drum δ 34 S signatures were significantly depleted (- 0.31‰) in the seagrass-dominated area, but enriched (2.03 to 3.78‰) in the other areas and indicated benthic but no pelagic sources of primary production. Mean snook δ 34 S signatures varied widely (0 to 20‰) among areas suggesting dependence on benthic (benthic algae and seagrass) and pelagic (phytoplankton) sources of primary production. Keywords Florida Bay . Everglades National Park . Stable isotopes . Diet . Spatial ecology . Trophic ecology Introduction Coastal estuaries are among the most productive and valuable natural aquatic systems on the planet, serving as nursery and foraging grounds for fish and other organisms, and providing a wide range of ecosystem services that benefit humans (Kearney et al. 2015). Sustained anthropogenic losses and deg- radation of estuaries means that they are also among the most threatened (Duke et al. 2007; Sheaves et al. 2017). Investigating the linkages and interactions among estuarine species and their prey is important to the understanding of ecosystem functioning and to the development of effective management strategies. The trophic ecology of large predatory marine fishes re- mains poorly understood, despite their being disproportionate- ly targeted by fishers (Frisch et al. 2014). Large predatory fishes that occupy the same habitat often have overlapping niche space, and understanding the process by which they have evolved to exploit different resources is fundamental to understanding their ability to coexist (Schoener 1974; Ross Communicated by Charles Simenstad Electronic supplementary material The online version of this article (https://doi.org/10.1007/s12237-018-00512-y) contains supplementary material, which is available to authorized users. * Christopher Malinowski cmalinowski@fsu.edu 1 Florida State University Coastal and Marine Laboratory, 3618 Coastal Highway, St. Teresa, FL 32358-2702, USA 2 Department of Biological Science, 319 Stadium Drive, Tallahassee, FL 32306, USA 3 Gulf World Marine Park, 15412 Front Beach Rd, Panama City Beach, FL 32413, USA 4 Department of Oceanography, Florida State University, Tallahassee, FL 32306-4320, USA 5 315 10th St, North Wilkesboro, NC 28759, USA Estuaries and Coasts https://doi.org/10.1007/s12237-018-00512-y