Texas A&M University – Corpus Christi
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The influence of habitat setting on community structure, organic matter, and consumer diets of subtidal oyster reefs in Matagorda Bay, Texas
No full textEstuaries contain a variety of habitats interconnected through flows of organic matter. The spatial arrangement of these habitats within the broader estuarine environment, known as habitat setting, can influence the composition organic materials and faunal communities they support. This dissertation explores the influence of habitat setting on subtidal oyster reefs by focusing on three key aspects: (1) oyster populations and faunal community structure, (2) organic matter composition and assimilation, (3) and bay-scale organic matter dynamics. Using a combination of faunal community metrics (i.e., abundance, biomass, diversity) and stable isotope analyses, results demonstrate that different habitat settings (such as bar and patch reefs) produce distinct effects on oyster populations and faunal communities.
In Chapter I, the importance of oyster reef habitat, the impact of habitat setting, the use of stable isotope analysis to study flows of organic matter, and the use of Matagorda Bay, TX as a study system are reviewed. In Chapter II, benthic macrofaunal community structure of oyster reefs changed with varying habitat settings, and bar reefs had greater and more variable oyster density and biomass compared to patch reefs. Benthic macrofaunal community composition differed between reef types, with bar reefs hosting more motile crustaceans, and patch reefs supporting more infaunal organisms. Results demonstrate habitat setting influences both oyster population and faunal community structure among subtidal oyster reefs.
In Chapter III, I examined organic matter availability and trophic structure between bar and patch oyster reefs. Results indicate the influence of habitat setting had no influence on organic matter composition and consumer diets among oyster reefs. Oyster reefs promote locally produced organic materials—especially phytoplankton and benthic microalgae—that are important for supporting community-wide faunal biomass. These findings demonstrate the ability of oyster reefs to provide a pool of organic matter that supports the majority of resident fauna biomass regardless of habitat setting.
In Chapter IV, I examined organic matter quantity and quality produced in various habitats across the Matagorda Bay estuary (i.e., seagrass beds, non-vegetated sediments, oyster reefs, open water), and incorporation of organic matter into the estuarine food using oysters as a recorder for resource use. Although organic matter composition was similar between oyster reef types, zooming out to the scale of the bay revealed variations in both the quantity and quality of organic matter, with higher biomass observed near the river delta and higher quality near the mouth of the bay. Additionally, sediments within seagrass beds had higher organic matter quantity and quality compared to non-vegetated sediments. Regardless of habitat setting, locally produced benthic microalgae emerged as a primary component of the oyster diet.
In Chapter V, I summarize of major findings of this dissertation and outline limitations, and recommendations for management and future work. Collectively, these findings highlight the role of habitat setting on ecological functioning at both local and ecosystem scales. As estuarine areas are increasingly threatened by stressors from anthropogenic- and climate-driven change, restoration and conservation efforts seek to mitigate damage. Understanding the influences, ranging from individual habitats to bay-wide dynamics, can inform creation of targeted goals and strategies for restoration and conservation efforts.Life SciencesCollege of Scienc
Interpreting biogeochemical processes through the relationship between total alkalinity and dissolved inorganic carbon: Theoretical basis and limitations
No full textThe marine carbonate system is influenced by anthropogenic CO2 uptake, biogeochemical processes, and physical changes that involve freshwater input and removal. Two frequently used parameters to quantify seawater carbonate system are total alkalinity (TA) and total dissolved inorganic carbon (DIC). To account for the physical changes, both TA and DIC are usually normalized to a reference salinity (i.e., nTA and nDIC), and then the relationship between nTA and nDIC is used to identify major biogeochemical processes that regulate the carbonate system, based on process-specific reaction stoichiometry. However, the theoretical basis of this interpretation has not been holistically examined. In this study, we validated this method under idealized conditions and discussed the associated assumptions and limitations. Furthermore, we applied this method to interpret field TA and DIC data from a lagoonal estuary in the northwestern Gulf of Mexico. Our results demonstrated that evaluating field data that encompass multiple stations and time periods could be problematic. In addition, various combinations of biogeochemical processes can lead to the same nTA–nDIC relationship, even though the relative importance of each individual process may vary significantly. Therefore, the stoichiometric relationship relying solely on TA and DIC data is not a definitive approach for uncovering dominant biogeochemical processes. Instead, measurements of process-specific parameters are necessary
Senator Truan and governor of Massachusetts, Michael Dukakis
No full textSenator Carlos Truan and Michael Dukakis pose for a photograph
Advanced computer architecture
No full textThe Branching Dilemma: Conditional branches are instructions that alter the program flow based on a condition. Processors typically fetch instructions sequentially. Encountering a branch creates a dilemma: Fetch the next instruction in sequence (assuming not taken). Fetch the target instruction of the branch (assuming taken)
Synthesis and characterization of aspartic acid-based tripeptide surfactants
Get PDFAmino acid-based surfactants (AABSs) provide a more environmentally friendly option than traditional surfactants. The introduction of amino acids into the polar headgroup increases bioavailability and biodegradation. This study aimed to introduce three amino acids at the polar headgroup to form a tripeptide surfactant. However, this study used aspartic acid (Asp) as a central amino acid at the polar headgroup and utilized its dicarboxyl groups to form peptide bonds with auxiliary amino acids, thus forming bifurcated tripeptide surfactants. This study used stoichiometric coupling with diisopropylcarbodiimide (DIC) and n-hydroxysuccinimide (NHS) to aid in synthesis. Products were examined with proton NMR (1H-NMR) to analyze synthesis results. Then, solubility tests were performed to determine relative solubility and preliminary critical micelle concentration (CMC) studies were conducted. The 1H-NMR results revealed that the current method of bifurcated tripeptide surfactant synthesis should be amended to obtain desired products, as a mixture of bifurcated tripeptide surfactants and linear dipeptide surfactants formed. Solubility tests revealed the products formed organogels, while preliminary CMC tests revealed an estimated CMC of 51.20 mM.Physical and Environmental SciencesCollege of Scienc
Dynamics of methane emissions from northwestern Gulf of Mexico subtropical seagrass meadows
No full textWhile seagrass meadows are perceived to be pertinent blue carbon reservoirs, they also potentially release methane (CH4) into the atmosphere. Seasonal and diurnal variations in CH4 emissions from a subtropical hypersaline lagoon dominated by Halodule wrightii in southern Texas, USA, on the northwest coast of the Gulf of Mexico were investigated. Dissolved CH4 concentrations decreased in the daytime and increased overnight during the diel observation period, which could be explained by photosynthesis and respiration of seagrasses. Photosynthetic oxygen was found to significantly reduce CH4 emissions from seagrass sediment. Diffusive transport contributed slightly to the release of CH4 from the sediment to the water column, while plant mediation might be the primary mechanism. The diffusive CH4 flux at the sea-air interface was 12.3–816.2 µmol/m2 d, over the range of the sea-air fluxes previously reported from other seagrass meadows. This was related to relatively higher dissolved CH4 concentrations (11.6–258.2 nmol/L) in a mostly closed lagoon with restricted water exchange. This study emphasizes seagrass meadows in the subtropical hypersaline lagoon as a source of atmospheric CH4, providing insights into the interactions between seagrass ecosystems and methane dynamics, with potential implications for seagrass meadow management and conservation efforts.This work was supported by Grants-in-Aid of Graduate Research Program of the Texas Sea Grant College Program from the NOAA, Texas A&M University-Corpus Christi Texas Comprehensive Research Funds, and Geological Society of America Graduate Student Grants
Proctoring modalities and the influence on HESI Exit Exam® scores: A comparison of two nursing cohorts
No full textNursing was voted the most trusted profession for the 22nd year in a row (Walker, 2024). To continue to be the most trusted profession, nursing faculty must ensure their students are prepared to enter the nursing profession. Students must be prepared to take the National Council Licensure Examination for Registered Nurses (NCLEX-RN®) licensing exam upon graduation. In 2020, the world changed with the emergence of COVID-19. COVID-19 brought many challenges to higher education faculty and students, including having to transition to emergency remote teaching (ERT) and learning (Hodges, et al., 2020; Iglesias-Pradas et al., 2021; Shin & Hickey, 2020). Handling how to administer tests was one of those challenges. The problem in the current study focuses on a cohort of nursing students who elected to enroll in a traditional face-to-face nursing program, but, due to unforeseen circumstances had to transition to emergency remote teaching. The purpose of this study was to, retrospectively; examine the scores of two groups of senior students at a public university in South Texas who took the HESI E2® in relation to proctoring modality. There was a statistical difference in proctoring modalities, with students using in person proctoring performing better than those using remote proctoring do. Since there was a significant difference noted between proctoring modalities and HESI E2® scores, a second question was included to compare each Cohort with the population mean. Cohort 2019 had a mean HESI® score of 945, which was well above the population mean of 847. Cohort 2020 had a decrease in the mean that coincided with an increase in the population mean, thus the proctoring modality for this cohort was a factor but not for the population.Educational Leadership, Curriculum & InstructionCollege of Education and Human Developmen
Focused Flows to Protect Estuarine Nursery Habitats
Get PDFAlong the Texas coast, estuaries provide essential habitats and nurseries for economically and ecologically important species. However, Texas estuaries are increasing in salinity from increased evaporation rates, shifting rainfall patterns, prolonged droughts, and agricultural, municipal, and industrial water diversions. The increased salinity may lead to reduced abundances of estuarine-dependent nekton. It has been proposed that the strategic release of freshwater to specific areas, or “focused flows”, can maintain nursery habitat suitability during droughts and promote the rapid recovery of estuarine-dependent species following droughts. This project aims to foster estuarine ecosystem health management and inform focused flow strategies by identifying the influence of salinity and freshwater inflow on nekton diversity and the habitat suitability of key indicator species from the seven major estuary systems along the Texas coast
Synergistic effects of petroleum production and marine environmental changes on oyster health
Get PDFA dissertation submitted in partial fulfillment of the requirements for the Degree of Doctor of Philosophy in Marine Biology at Texas A&M University-Corpus Christi.Polycyclic aromatic hydrocarbons (PAHs) have been well described as toxic byproduct of the incomplete combustion of petroleum compounds. In the environment, the high volatility of PAHs causes them to degrade into various compounds, some of which are of higher toxicity than that of the parent PAH. Therefore, the toxicity of photo-exposed PAHs should be investigated as a supplement to existing knowledge of the toxicity of PAHs. As the ever-dynamic environment is a complex system of abiotic and biotic factors, it is not surprising that some of these factors such as temperature and salinity may affect how PAHs photodegrade. In this study, emulsions of two target PAHs, anthracene and pyrene were produced using DMSO as a solvent and then diluted into either deionized water or 30-PSU saltwater. These mixtures were subsequently photodegraded using the Suntest CPS+ for 0, 1, and 2 hours, in which the 0 hrs time represents unexposed PAHs. Live eastern oysters (Crassostrea virginica) were collected for whole organism assays in addition to larval and cell culture assays. Larvae and primary cardiomyocyte cell cultures were procured from the adult oysters and prepared for the toxicity assessment of photodegraded PAHs. A dosage of 0.1 ppm, near the solubility limit of, photodegraded anthracene or pyrene were administered to the ambient seawater of the adults and larvae, or to the cell culture medium for an acute 24-hr exposure period. The results suggested that the primary cardiomyocyte cell culture was not sensitive to treatment by either the original or photodegraded PAHs. Adult and larval oysters exposed to the PAH mixtures experienced an upregulation in stress response and inflammatory pathway gene expression, although the larval assay was shown to be more variable, thereby being less stable, than the adult assay. The stress response in the larvae showed a strong correlation to reduced activity level, which was also correlated with an upregulation in what is likely a shell formation as a protective response to the environmental contaminant. Across all the treatments, neither the virgin anthracene nor pyrene exhibited high levels of toxicity; it was the photodegraded mixtures that caused the majority of the observed stress responses. Photodegraded anthracene was noted to exhibit the most toxicity after 1 hour of photo-exposure, whereas pyrene exhibited the most toxicity after 2 hours of photo-exposure or reduced to only 1 hour of photo-exposure in artificial sea water. It is likely that any chemicals generated in the first hour of anthracene photodegradation are quickly becoming degraded, resulting in a less harmful mixture. Pyrene on the other hand could be more stable and its toxic effect on the environment may have a longer residence time than that of anthracene. It has been speculated that the generation of anthraquinone during photoexposure is the primary toxicant among the degradation products of anthracene. However, additional tests using pure anthraquinone as the experimental treatment did not align with this hypothesis, and the increase in toxicity of the photodegraded mixtures could not be explained by the generation of anthraquinone. Therefore, other chemicals produced during photoexposure are more likely to contribute to the stress response, and the role anthraquinone plays in the toxicity of anthracene may be much less than previously thought. Saltwater, on the other hand, may accelerate the production of toxic compounds during photoexposure. Thus, this study confirms the importance of increasingly complex, multi-faceted toxicological studies in order to fully characterize the synergistic effects of the environment and the contaminants on the organisms and overall health of the ecosystem.Life SciencesCollege of Scienc
Senator Carlos F. Truan in a crowd at Dukakis evenet
No full textSenator Truan amidst a crowd of people at a rally for the 1988 presidental election. One attendee holds a sign that reads "Goliad County for Dukakis"