Evaluation of blood biochemistry in Texas diamondback terrapin (Malaclemys terrapin littoralis) within the Mission-Aransas and Nueces estuaries

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A thesis Submitted in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE in MARINE BIOLOGY from Texas A&M University-Corpus Christi in Corpus Christi, Texas.
Freshwater inflow is essential for providing key nutrients for estuarine environments. However, reduction of freshwater inflow can alter the function and structure of estuarine conditions and resources with detrimental consequences. For example, construction of the Choke Canyon and Wesley Seale dams have altered the Nueces Bay by reducing freshwater inflow causing increased salinity in the upper portion of the estuary. Brackish waters require osmoregulating organisms, such as diamondback terrapin (Malaclemys terrapin), to expend a great deal of energy maintaining homeostasis in the face of the widely varying salinities. In South Texas, areas in the upper estuary that are typically brackish may become hypersaline during summers or times of drought. Thus, terrapins living in South Texas estuaries may be subject to a great deal of physiological stress from high and/or varying salinities. This study evaluated the physiological effects of salinity on stress hormone production and assessed baseline blood chemistry and electrolyte values in the Texas diamondback terrapin (Malaclemys terrapin littoralis) within the Nueces and Mission-Aransas Estuaries. Terrapins (n = 110) were captured during April 2015 – November 2015 and May 2016 – August 2016 from Aransas Bay, Nueces Bay, and Oso Bay. Water parameters were recorded for each sampling event. A blood sample was drawn from the subcarapacial sinus vein; initial blood glucose concentrations and morphometric data were recorded for each individual captured. Plasma samples were analyzed to determine the stress hormone concentrations of corticosterone, aldosterone, and prolactin using spectrophotometry techniques and commercially available enzyme-linked immunosorbent assay (ELISA) kits. Subsamples of plasma were analyzed using an electrolyte panel (Na+, Cl-, K+, and CO2) and colorimetric techniques with commercially available reagents to determine plasma concentrations of glucose, albumin, total protein, total bilirubin, creatinine, blood urea nitrogen, and uric acid. Salinity and blood biochemistry measurements for terrapins captured on the same day in the same trap were averaged to provide an accurate representation of each salinity. Using canonical discrimination, each bay was successfully separated with canonical axis 1 accounting for 93% of the variance and canonical axis 2 accounting for 7% of the variance. Data for all stress hormone and blood biochemistry variables were tested using discriminant analysis resulting in a 100% classification accuracy for each of the bays. Significant correlations were found between salinity in Nueces Bay and plasma concentrations of sodium, chloride, and blood urea nitrogen, and salinity in Oso Bay had a significant correlation with aldosterone plasma concentrations. Significant differences in stress hormone and blood biochemistry concentrations were observed for each bay using ANOVA and Duncan’s multiple range test. The results of this research provide the first physiological assessment of Texas diamondback terrapins under variable salinity conditions utilizing hormones and blood biochemistry concentrations.
Life Sciences
College of Science and Engineering