Trophic Structure in Salt Marsh Tidal Creeks Arrayed Along a Gradient of Urbanization

The northern Gulf of Mexico, specifically coastal Mississippi, is undergoing rapid urbanization that may impact the habitat value of salt marsh ecosystems for many fishes and, consequently, alter their suitability for the maintenance and regulation of fish populations. In this study we use several metrics as indicators of altered trophic structure in salt marsh tidal creeks in highly urbanized coastal landscapes.  First, the diet composition of both spot (Leiostomus xanthurus) and Gulf killifish (Fundulus grandis) differed among intact natural salt marsh landscapes (IN) and completely fragmented coastal landscapes (CF).  For both species, the proportion of individuals with empty stomachs was significant greater in CF landscapes (40-60%) than in either partially fragmented salt marsh landscapes (PF) or IN landscapes (15-25%).  Further, a Bayesian stable isotope mixing model, using the stable isotopes of carbon, nitrogen, and sulfur, was used to quantify the contribution of autotrophs and potential prey items to the isotopic signatures of both spot and Gulf killifish.  These results suggest that in IN and PF landscapes production is derived from benthic microalgae, C3 plants (i.e., Juncus romerianus), and C4 plants (i.e., Spartina alterniflora).  In the CF landscapes, however, production is driven principally by C4 plants.