Freshwater inflow effects on mobile epifauna and estuarine dependent crustaceans in Rincon Bayou in the Nueces Delta
Gordon, Amanda Mae
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Rincon Bayou is a negative estuary located in the western region of the Nueces Delta, north of Nueces Bay in Corpus Christi, Texas, and has been affected by anthropogenic freshwater withdrawals, impacting the epifaunal community. For over two decades, there have been adaptive management activities to mitigate potential effects from water withdrawals, including establishment of inflow requirements, construction of a pipeline to enhance flow to the marsh, and monitoring to assess the extent the region has been affected. Salt marshes provide habitat and refuge to a multitude of species at various trophic levels. From a fisheries standpoint, this region serves as juvenile and refuge habitat for several recreationally and commercially valued marine species of the Texas coast. This study compared three sites and three years of sampling (2010, 2014-2015) in Rincon Bayou to determine spatial and temporal effects of natural and pumped inflows on the mobile epifauna, particularly, on post-larval and juvenile recruits of brown shrimp (Farfantepenaeus aztecus), white shrimp (Litopenaeus setiferus), and blue crab (Callinectes sapidus). The results indicated that physical variables, depth and dissolved oxygen, explained dissimilarities within the epibenthic community more than salinity, suggesting that Rincon Bayou exhibits signs of being more than just a salinity-stressed environment. Signs of disturbance were recognized with the presence of freshwater indicator species, particularly significant following the May and June 2015 spring freshets. The epifaunal community of Rincon Bayou experienced some enhancement, where abundance, biomass, species richness, and diversity were higher for the year 2015 in comparison to previous years of this study. Fish exhibited a trend in higher biomass and diversity, increasing each year of the study, but an overall decline in abundance. In the crustacean community, brown shrimp displayed declines in abundance and biomass from 2010-2015, and white shrimp experienced a decrease in biomass. Blue crab populations also experienced a reduction in biomass, but showed signs of improvement in 2015. The overall findings of this study indicate that the region is utilized by several commercially valued species, and current management practices are improving the ecosystem of Rincon Bayou at the epibenthic level. However, current pumping regimes may have a negative impact on the environment as a whole, where magnitude, timing, and duration of freshwater events may alter recruitment of estuarine-dependent species.
A thesis Submitted in Partial Fulfillment of the Requirements for the Degree of MASTER of SCIENCE in FISHERIES AND MARICULTURE from Texas A&M University-Corpus Christi in Corpus Christi, Texas.