Life Sciences Commons^™

Ecological And Oceanographic Influences On Leatherback Turtle Behavior And Scyphozoan Jellyfish Distributions In The Gulf Of Mexico, Katrina Aleksa

Dissertations

Leatherback turtles (Dermochelys coriacea) are a wide-ranging, oceanic species that feed exclusively on gelatinous zooplankton. Leatherback have been spotted in the Gulf of Mexico (GoM) for several decades and consistently had a high level of interactions with longline fisheries. However, no quantitative studies have been performed to address the spatiotemporal distribution of these turtles in the GoM. This research determines 1) leatherback movements and high-use areas in the GoM, 2) their association with oceanographic features, 3) the distribution and density of two abundant medusae in the northern GoM and any association with biophysical parameters, and 4) the body …

Macrobenthic Communities In The Northern Gulf Of Mexico Hypoxic Zone: Testing The Pearson-Rosenberg Model, Shivakumar Shivarudrappa

Dissertations

The Pearson and Rosenberg (P-R) conceptual model of macrobenthic succession was used to assess the impact of hypoxia (dissolved oxygen [DO] ≤ 2 mg/L) on the macrobenthic community on the continental shelf of northern Gulf of Mexico for the first time. The model uses a stress-response relationship between environmental parameters and the macrobenthic community to determine the ecological condition of the benthic habitat. The ecological significance of dissolved oxygen in a benthic habitat is well understood. In addition, the annual recurrence of bottom-water hypoxia on the Louisiana/Texas shelf during summer months is well documented.

The P-R model illustrates the decreasing …

Spatial, Temporal And Demographical Analysis Of Gulf Of Mexico Research Priorities, The Effect Of The Deepwater Horizon Oil Spill, Stephen Hiller Sempier

Dissertations

A set of twenty equally-weighted national ocean research priorities were define in 2007, but it was not clear if these priorities applied for the Gulf of Mexico. A series of three longitudinal surveys of people who conduct research, sponsor research or use research for professional or recreational purposes was released that focused on the twenty research priorities and asked people how they rated each. A convenience sampling method was employed, which suggests that the results are constrained to the survey respondents and should not be extrapolated to a larger population. More than 1,500 people completed the 2013 GMRP survey and …

Phytoplankton Community Distribution And Light Absorption Properties In The Northern Gulf Of Mexico, Sumit Chakraborty

Dissertations

The theme of this dissertation was to understand the spatio-temporal dynamics of the phytoplankton community, its light absorption properties, and its relationship to underlying physicochemical processes. Understanding these phenomena will benefit efforts to predict pathways of carbon transformation in the ocean, to estimate primary productivity (PP) and to characterize distributions of phytoplankton communities using ocean color remote sensing.

This research entailed four different studies, which address different objectives. The first two studies dealt with phytoplankton community composition and its relationship to environmental variables. A chemotaxonomic approach was used, which was successful in revealing distinct phytoplankton assemblages in distinct water mass …

Marine Fungi Of U.S. Gulf Of Mexico Barrier Island Beaches: Biodiversity And Sampling Strategy, Allison Kathleen Walker

Dissertations

Marine fungi are an important but often overlooked component of marine ecosystems. Primarily saprotrophic, they are vital to coastal nutrient cycling processes and food webs. However, basic marine fungal distribution data are lacking in many parts of the world, as is knowledge of the sampling intensity required to characterize the biodiversity of these communities. The roles of substrate, season and latitude in shaping intertidal ascomycete community structure were examined for the U.S. Gulf of Mexico, and the role of sampling frequency on species richness estimates was also addressed. Best sampling practices were developed and 750 collections of beach detritus, sand …

Fluorescence And Size Characterization Of Dissolved Organic Matter In Riverine And Sea Waters In The Northern Gulf Of Mexico, Zhengzhen Zhou

Dissertations

Riverine export of dissolved organic matter (DOM) is an important component in marine carbon budget but the composition and phase partitioning are poorly quantified. Monthly water samples were collected from the lower Mississippi and Pearl rivers between January 2009 to August 2011 for DOM characterization using the fluorescence excitation emission matrix (FluoEEM) technique, coupled with parallel factor analysis (PARAFAC), and flow field-flow fractionation technique. DOM in the Pearl River showed higher dissolved organic carbon (DOC) concentration, temporal fluctuation, and aromaticity, reflecting instantaneous inputs of DOM from local soil and plant litter. In contrast, DOM in the Mississippi River exhibited lower …

Effects Of Hypoxia And 4-Tert-Octylphenol On Gene Expression Profiles Of The Sheepshead Minnow (Cyprinodon Variegatus), Arthur Alan Karels

Dissertations

Hypoxia occurs in estuaries of northern Gulf of Mexico and world-wide, with increasing frequency/severity via eutrophication and anthropogenic influences. Hypoxia inducible factors (HIFs) form transcriptional complex and bind DNA at hypoxia responsive elements (HREs) in promoter regions of genes needed for systemic and cellular adaptation of fish to low dissolved oxygen (hypoxia, DO <2.0 mg/ml). Hypoxia-induced activation of HIF-αs can lead to a cascade of downstream activation, such as erythropoietin (EPO). Return to normal DO levels (normoxia), prolyl hydroxylases (PHDs) are activated to degrade HIF-αs back to baseline. Fish are affected by environmental estrogen mimics, like 4-tert-octylphenol (4tOP), binding estrogen receptor alpha (ERα) at estrogen responsive elements (EREs) and activating genes vitellogenin (VTG). Previous research showed overlap or crosstalk between these two mechanistic pathways. Hypoxia triggers unknown factors regulating ERE-mediated ERα signaling pathway, and stressor combinations could increase/decrease hypoxic or endocrine pathway. Research examined molecular/physiological effects of hypoxia (acute and chronic, moderate and severe) and 4tOP (~60μg/L)on adult male and/or female sheepshead minnow (Cyprinodon variegatus). Three genes identified, cloned, and sequenced (HIF-1α, HIF-2α, and PHD3), plus previously identified genes EPO and VTG, were examined in liver/testes exposed to hypoxia and/or 4tOP for cellular/physiological changes. Endpoints examined included mRNA expression from real-time PCR of HIF-1α, HIF-2α, PHD3, EPO, and VTG using cDNA from total RNA extracts, and microarray analyses of genes expressed during the transition from hypoxia back to normoxia. Phylogenetic analyses confirmed isolation of two HIF-α isofoms (HIF-1α and HIF-2α) and the PHD3 isoform. Significant up-regulation of PHD3 occurred within 10 hrs of chronic hypoxia, and persisted when severe (1.5 mg/L) and declined when moderate (~2.5mg/L). Significant up-regulation of HIF-1α and EPO occurred within 30 minutes to 2 hours of onset of acute severe and very severe (~1.08mg/L) hypoxia. Hypoxia acted similar to an estrogen mimic, with huge up-regulation of VTG gene expression in males, and increased VTG levels (additive effect) when hypoxia was combined with 4tOP. Microarray analyses showed 125 genes with significant transcriptional change, with up- or down-regulation from transitions of: (1) hypoxia (72 hrs) to normoxia (74 hrs) and (2) hypoxia+4tOP (72 hrs) to normoxia+4tOP (74 hrs).

Life History And Habitat Use Of The Juvenile Alabama Shad (Alosa Alabamae) In Northern Gulf Of Mexico Rivers, Paul Fraser Mickle

Dissertations

The Alabama shad, Alosa alabamae, is an anadromous species that is in decline and has seen extirpations from impoundments as well as decreased water quality. Alabama shad live in the Gulf of Mexico and ascend Northern Gulf of Mexico Drainages to reproduce early in the year (January-May). The juveniles spend the majority of the year in these freshwater systems before emigrating out to the Gulf of Mexico as late as December.

This dissertation focuses on the juvenile life stages that occur within the Northern Gulf of Mexico drainages. Spawning conditions of the river, as well as the habitat and diet, …

Factors Influencing The Environmental Quality Of The Bay Of Saint Louis, Mississippi And Implications For Evolving Coastal Management Policies, Pradnya Ankush Sawant

Dissertations

The Bay of St. Louis, MS is a small northern Gulf of Mexico estuary that has been identified by the Mississippi Department of Environmental Quality (MDEQ) as an impaired waterbody for its designated uses, mainly due to the presence of pollutant pathogens. A systematic study of this estuary was important to understand the behavior and responses of the bay to several natural and anthropogenic forcing factors. A 14- month long study (bimonthly sampling) to evaluate its environmental quality was undertaken from April 2003 to May 2004. Environmental quality was defined as "the health of an ecosystem characterized in terms of …