Abstract
Few studies have quantified trophic relationships in seagrass environments at the regional scale, making it difficult to make comparisons of trophic structures across seagrass ecosystems. We conducted a large-scale study at six sites across the northern Gulf of Mexico (Lower Laguna Madre, TX; Redfish Bay, TX; Chandeleur Islands, LA. St. George Sound, FL; Cedar Key, FL; and Charlotte Harbor, FL) during August–September 2018 to examine how trophic relationships in turtlegrass-dominated ecosystems vary across ~1500 km and 15 degrees longitude. We measured bulk carbon (δ13C) and nitrogen (δ15N) stable isotopes for 21 representative nekton species (n = 602 individuals) and 20 potential basal autotrophic carbon sources (n = 331 samples) that were common across all sites. Divergence in isotopic space and pairwise niche overlap between species and sites was evaluated using Stable Isotope Bayesian Ellipses (SIBER) and Niche Region and Niche Overlap Metrics for Multidimensional Ecological Niches (nicheROVER) techniques. Preliminary results indicate that seagrasses are an important basal carbon source for nekton species throughout the region, that variability in seagrass δ15N is similar among sites (-2.4 to 6.6), and that seagrass δ13C values may be more enriched in the western (-13.1 to -3.2) than the eastern Gulf (-18.9 to -9.6). These data provide useful information on food web structure in turtlegrass ecosystems at a macroecological scale that is directly relevant to natural resource management of these productive systems.
