Drivers of Regional Variability in Producer and Consumer Stable Isotope Values (δ13C and δ15N) Within Turtle Grass-Dominated Meadows Across the Northern Gulf of Mexico Estuaries and Coasts

Estuaries within the northern Gulf of Mexico (nGOM) exist along a climatic gradient with higher rates of precipitation and freshwater inflow in the northeast and lower precipitation rates and freshwater inflow in the southwest. A synoptic field survey was conducted during August–October 2018 to quantify the influence of multiple environmental drivers, including salinity, temperature, depth, and light attenuation on producer and consumer stable isotopes in seagrass ecosystems across six estuaries (Lower Laguna Madre, Texas; Coastal Bend, Texas; Chandeleur Islands, Louisiana; St. George Sound, Florida; Cedar Key, Florida; and Charlotte Harbor, Florida) that span this climatic gradient. Carbon and nitrogen stable isotope values (δ13C and δ15N) for 16 representative nekton taxa (n = 596 individuals) and 7 potential basal resources (n = 304 samples) were measured across all sites. Taxon-specific differences in stable isotope values were quantified, and principal components analysis, correlation, and regression tests were used to quantify potential environmental drivers of δ13C across the nGOM. Producer and nekton δ15N had site and taxa-specific variability, but did not exhibit any Gulf-wide patterns. Taxa carbon isotope values were regionally specific with lower δ13C in the eastern nGOM and higher δ13C in the western nGOM and Spearman correlations indicated moderate to strong positive relationships between δ13C and salinity for most taxonomic groups across the nGOM (range r, 0.56–0.93). This study provides an important snapshot of isotope spatial variation in seagrass communities across the nGOM and reveals the sensitivity of seagrass communities to meteorological and climatic drivers across the nGOM. Grant no. NA17NOS4510093