Nekton community characterization of the lower Brazos River with an emphasis on larval Atlantic Croaker, Micropogonias undulatus, trophic dynamics

From December 2016 – October 2017, 50 collections of 150 replicate otter and beam trawls were collected at five different sites, three different seasons, and three different flow tiers along the Brazos river estuary. A total of 96 Atlantic Croaker, Micropogonias undulatus, and 40 particulate organic matter (POM) samples were collected and analyzed for 13C, 15N, and 34S. Catch per unit effort (CPUE) and taxa richness, as well as, Atlantic Croaker CPUE were all significantly greater at collection sites nearest the Gulf of Mexico. Collection sites nearest the Gulf of Mexico also displayed significantly enriched 13C, 34S, and POM 34S levels in Atlantic Croaker tissue (Tables 32 – 33 and 44). The observed patterns in stable isotopes were likely caused by the stratification of the salt wedge caused by variations in freshwater inflow transporting upstream sources of carbon and enriched sources of 13C, 34S derived from tidal transport of marine water and associated sources of carbon and sulfur into the estuary. These findings demonstrate the strong linkage of freshwater inflow, downstream transport of carbon and nitrogen and estuarine productivity.