Theses
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Item A diversity baseline of benthic macrofauna along the northwestern insular slope of Cuba (Gulf of Mexico)(2023-12) Schiereck, Samantha; Montagna, Paul; Pollack, Jennifer; Schwing, PatrickThe Gulf of Mexico (GoM) is a unique ecosystem due to the physical characteristics influenced primarily by the Mississippi River in the North and the Loop Current, which originates in the south, resulting in a gradient of organic to carbonate sediment composition. The continental slope of the northern (US) and southwestern (Mexico) portions of the GoM are generally well studied; however, very little is known about the southeastern GoM along the slope of Cuba. To fill this knowledge gap, sediment cores were collected in 2017 at nine stations (974–1580 m depth) to gather baseline data and determine controls on the deep-sea benthic macrofauna community. Oceanographic data indicated a stratified water column typical of an oligotrophic ocean and no evidence of hypoxia. Sediment texture and composition indicated a west-east gradient likely determined by downslope transport of terrigenous material in the eastern part with a high proportion of carbonate in the west. Heavy metals (Cu, Hg, Pb, and Zn) at concentrations known to cause benthic effects were present in the east near the major city of Havana, with the macrofauna community showing characteristics indicative of environmental stress. Stations had a low overall average diversity (15 families/79 cm2) and abundance (7,980/ m2), with high variability among replicates within the stations. The diversity was 48% less, and the abundance was 14% less than in the northern GoM. The major factors influencing macrofauna communities in the continental slope off northwestern Cuba are most likely the lack of organically rich sediment, low sediment deposition rates, and the strong current.Item Accumulation of epiphytes on Halodule Wrightii in response to nutrient enrichment in East Flats, Corpus Christi Bay and Nighthawk Bay, Upper Laguna Madre, Texas(2010-08) Sweatman, Jennifer L.; Cammarata, Kirk; Smee, Lee; Shirley, Thomas; Withers, Kim; Mott, Joanna; Pezold, FrankIncreased epiphyte abundance on seagrasses is often associated with anthropogenic eutrophication of estuarine ecosystems, but the quantitative relationships are complex and not fully understood. A nutrient enrichment experiment was conducted at two sites during three seasons to measure epiphyte accumulation on Halodule wrightii and artificial seagrass substrates. A novel fluorescence imaging technique, based on excitation of phycobilin and fucoxanthin accessory pigments, was used to quantify epiphyte abundance. For natural seagrasses, significant dose-dependent increases in epiphyte accumulation occurred due to the introduction of nutrients at East Flats, during early summer and fall sampling seasons. Significant nutrient responses were also detected during late summer at East Flats, and during early summer and fall only at a hypersaline lagoon site, Nighthawk Bay. Additionally, nutrient enrichment caused significant decreases in combined seagrass and epiphyte biomass across all seasons at Nighthawk Bay, and during late summer at East Flats. At East Flats, biomass increased with increasing nutrient treatments during early summer and fall seasons. Artificial substrates failed to corroborate results of the natural seagrass experiment; however, a change in species composition was evident, but results were inconsistent across seasons and sites. These findings imply that epiphyte abundance is sensitive to nutrient enrichment under a wide range of ambient conditions, including different predominant grazer abundances, and is likely to increase with eutrophication.Item Analyses of biological communities and development of indices of biotic integrity for monitoring tidal streams along the upper Texas coast(2020-05) Margo, Abraham; Pollack, Jennifer Beseres; Withers, Kim; Tolan, JamesTidal streams along the upper Texas coast are characterized by large heterogeneity in abiotic conditions and biotic communities, posing challenges to managers seeking to assess their ecological condition and develop effective management strategies. There is currently no standardized protocol for assessing ecological condition in Texas tidal stream systems. The goal of the current study was to create multimetric indices of biotic integrity (IBIs) from nekton and benthic macroinfaunal community metrics that were effective in discriminating between degraded “test” and non-degraded “reference” streams (classified by watershed land-cover data). Fifteen tidal streams were sampled twice per year in 2018 and 2019 to assess water quality, nekton, and benthic macroinfaunal dynamics. In order to create the multimetric indices of biotic integrity, multiple univariate metrics were assessed to determine the extent to which they differentiated between test and reference sites. Selected metrics were used as components in developing the multimetric IBIs, which give higher scores to samples that have similar biotic characteristics to our reference condition samples. Multivariate analyses provided a complementary approach to selection of IBI metrics by visualizing, comparing, and identifying community-level changes as well as taxa that associate with the test or reference condition. Results indicated that overall differences in biological communities between test and reference sites were often not extremely strong. Multivariate analyses indicated nekton communities exhibited stronger differentiation between test and reference samples whereas benthic macrofaunal communities were influenced more by year to year variations. However, several univariate metrics highlighted components of communities that did differ between test and reference sites, and these metrics were used to form the IBI. Comparing IBIs for both nekton and benthic macroinfauna can provide a more comprehensive understanding of biotic integrity in tidal streams than focusing on one or the other. Results should be interpreted with some caution but could help inform water resource management decisions that seek to support aquatic life use while balancing human needs for food, recreation, and industry.Item Antibacterial properties of plant extracts from curanderismo (Mexican herbal medicine) on pathogenic strains of Vibrio Vulnificus isolated from the Coastal Bend region of Texas(2022-12) Patel, Hinal Arvindbhai; Buck, Gregory; Sparks, Mary Jean; Daru, BarnabasVibrio vulnificus, a Gram-negative mesophilic bacterium that belongs to the gamma Proteobacteria phylum and family Vibrionaceae, is halophilic and asporogenous and is autochthonous to marine and estuarine environments. Between April and October, the organism reaches peak levels in the Gulf of Mexico. Previous studies indicate that antibiotic resistance is increasing in Vibrio vulnificus. Finding a solution to this antibiotic resistance problem is critical for both aquaculture and medical care with persons exposed to Vibrio. One possible treatment modality to control the effects of antibiotic resistant bacteria is Curanderismo, a popular alternative plant-based medicine derived from Mexican culture, which has been overlooked by scientific investigation and may be used in lieu of pharmacologic antimicrobial agents. This study hypothesizes that certain plants may be used for treatment of antimicrobial-resistant strains (AMR) of Vibrio vulnificus. The objectives are to (1) investigate the effect of active plant extracts and tinctures on strains of Vibrio vulnificus by Kirby-Bauer disk diffusion susceptibility testing; (2) Investigate the effect of active plant extracts on the ability of Vibrio vulnificus to form biofilms, which indirectly observe quorum-sensing (QS)-regulated virulence traits. Ten typical herbal treatments of Curanderismo used to treat wounds and infections in south Texas were made as tinctures in against the four Vibrio vulnificus strains. In addition, biofilm assays revealed these six plant extracts showed better antimicrobial and anti-biofilm activity compared to the bacterial control. These findings demonstrate that certain plant tinctures may be plausible treatment methods and future studies will investigate specific plant tinctures on a wider range of south Texas Vibrio vulnificus strains.Item Applicability of the microfragmentation technique to propagate corals in a fisherfolk community in the Philippines(2019-12) Broquet, Nicole C.; Scarpa, John; Siccardi, Anthony; Pollack, Jennifer Beseres; Vaughan, DavidCoral nursery implementation is becoming a highly prevalent method of coral restoration in the Philippines. These nurseries primarily focus on fast-growing branching corals and do not commonly include massive corals. This is due to the slow growth rate and morphology of these corals, which are not conducive to traditional nursery methods. Microfragmentation is a relatively new technique that has displayed positive results for massive coral propagation. This method utilizes small coral fragments (≈1-3 cm) that are mounted on platforms, then placed in ex-situ or in-situ nurseries. The fragments exhibit rapid growth, which decreases the duration of the nursery phase before transplantation. Though microfragmentation is becoming more practiced, there is no published literature specifically focused on this method in the Philippines. The present study aimed to determine if: 1) coral specimen (i.e., putative genotype) significantly influenced growth, and 2) this method was viable in a fisherfolk community in the Western Visayas of the Philippines. Five corals of opportunity (putative genotypes) of the lobe coral, Porites lobata, were fragmented with hammer and chisel by several volunteer fisherfolk. The fragments were cultured from April-August 2018 in an in-situ fixed-leg nursery at a depth of approximately 2m. Maintenance was performed weekly and measurements of growth (i.e., volume change) were conducted monthly. The fragments were then transplanted to a selected restoration site and monitored for one month. A hierarchical Bayesian log-linear regression model indicated that 59.7% of growth (volume change) variation was attributed to coral specimen (i.e., putative genotype) and 26.4% of growth variation was attributed to the individual fragment. Overall, the average monthly increase in particular specimen’s fragment volume was 23.5% per month (95% CI, 3.43% - 43.9%/month) with the greatest monthly increase for a specimen at 30.1% per month (95% CI, 19.3 – 40.3%/month). Mean tissue spreading was determined to be 43.24cm2 /month (95% CI 44.5 – 79.4 cm2 /month) and mean linear extension was estimated to be 1.55 cm/month (95% CI, 0.92 – 2.02 cm/yr). Though high growth rates for P. lobata were documented in this study, nursery maintenance was significant due to lack of resources and location of nursery. This method may be viable and highly beneficial in established coral nurseries in the Philippines, but may not be feasible in a remote fisherfolk communityItem Assessing embryonic toxicity and end fates of nanoplastics in freshwater environments using gastropod Biomphalaria Glabrata(2022-07-22) Merrill, MacKenzie Leigh; Xu, Wei; Bahr, Keisha; Wagner, Daniel; Mozzachiodi, RiccardoThe wide use of plastics has resulted in not only the accumulation of macroplastic pollution in the aquatic environment but also plastic particles at micro and nano levels (MPs and NPs). Accumulation of these MPs and NPs have numerous adverse effects on the morphology, behavior, and reproduction of living organisms. In this study, we investigated the effects of NPs on the embryonic development of Biomphalaria glabrata, a commonly used gastropod in toxicology studies. This study identified the adsorption of NPs by the embryos of B. glabrata and showed evidence of NP absorption by the hatched juveniles. NP bioaccumulation subsequently triggered the alteration in the expression of several stress response genes, including heat shock protein-70 (HSP70), cytochrome P450 (CYP450), and macrophage migration inhibitory factor (MIF). With the influence of NPs, the hatching rates of B. glabrata embryos varied depending on the sizes of NPs. In addition, the NPs with mean diameters of 1.0 µm or 0.03 µm led to higher embryo mortality rates than 0.5 µm NPs. This preliminary study demonstrated the impact of NPs on the development of B. glabrata embryos. Further studies on the mechanism of NP toxic effects are desired.Item Assessing the acute toxicity of photodegraded anthracene with in vitro and in vivo skin models(2022-07-20) Brzezinski, Molly; Xu, Wei; Seemann, Frauke; Conkle, Jeremy; Zhu, LinThe Gulf Coast of Texas is heavily inundated with petroleum refineries that release Polycyclic Aromatic Hydrocarbons (PAHs) into nearby waters, and these chemicals may pose a threat to human health when they interact with environmental conditions. PAHs are a group of hundreds of different chemicals, and the Environmental Protection Agency has identified 16 priority PAHs. Many of these chemicals are acute skin irritants and can cause skin, lung, bladder, and liver cancer with chronic exposure. Humans can be exposed when they interact with contaminated air, soil, and water. Recent studies have demonstrated that abiotic factors such as UV light, salinity, and pH can modify PAH structure, however, it is unknown how these modifications affect acute toxicity to the human skin barrier. The objectives of this study were to characterize the phototoxic effects of a priority PAH, anthracene by testing photodegradation treatments on cell culture and animal models. Gas chromatography and mass-spectroscopy confirmed the presence of 1,9-anthraquinone and phthalic acid, both known skin irritants, in photodegradation products. Keratinocyte cell culture was used to assess the impacts of photodegraded anthracene on cell migration, viability, and stratification development. We found that longer photodegradation times resulted in decreased cell viability and increased migration. A unique three-dimensional stratification assay demonstrated that photodegraded anthracene reduces differentiation in apical keratinocytes. Relative gene expression analysis suggests that keratinocytes bypass TLR-4 activation and utilize IL-1?, IL-1?, and TNF-? to produce an inflammatory response. Mus musculus studies indicate that extracellular matrix remodeling may be induced by 4, 8, and 24-hour photodegraded intermediates by keratinocyte-derived Il-1?, S100a9, Mmp1, and Connexin43. The results of this study indicate that photodegradation can produce intermediates that may elicit dermal inflammation, and the presence of these intermediates should be evaluated in bays with high foot-traffic.Item Assessment and valuation of nitrogen mitigation ecosystem services in natural and restored wetlands of the Texas coastal bend(2020-05) Hayes, Lydia; Hayes, Lydia; Zhang, Lin; Williams, Lauren; Zhang, Lin; Williams, Lauren; Reese, Brandi; Reese, Brandi K.Eutrophication leads to poor water quality, hypoxia, and biodiversity loss in aquatic ecosystems, which is a major issue in the Gulf of Mexico and its surrounding estuaries. It is largely caused by excess nutrients in aquatic environments. With population rising along the Texas coast, there is an increase in nitrogen-based nutrients output, through wastewater and agricultural runoff. It is critical to reduce nutrients input to nitrogen-limited waters to improve water quality and eliminate eutrophication. Wetlands are important ecosystems that offer many ecosystem services including nitrogen mitigation. Denitrification is the main pathway for removing excessive nitrogen-based nutrients in wetland sediments. In this study, nitrogen mitigation was quantified through potential denitrification measured in five wetland sites, two restored and three natural ones. Our results showed that the age of wetlands is a major factor regulating denitrification rates, with lowest average annual rates found in two restored sites, Egery Flats and the Nueces Bay restored marsh (11.46 and 10.85 kg N∙ha-2∙yr-1, respectively). Significantly higher rates were found in natural wetland sites, with mean annual rates of 22.5, 29.39, and 39.27 kg N∙ha-2∙yr-1 measured for the Aransas River Estuary, Oso Bay marsh, and the Naval Airbase Bridge, respectively. Temperature was another influencing factor for denitrification rates in three of the five sites. The seasonal denitrification rates measured in this study were used to quantify the economic value of nitrogen mitigation ecosystem services in the two restored wetland sites. The replacement cost was $36,565∙yr-1, and $8,125∙yr-1, for Egery Flats and Nueces Bay restored marsh, respectively, which is an equivalent value of $13.55∙kg N-1 removed.Item An assessment of seagrass evolutionary diversity in the Anthropocene(2021-08) Rock, Brianna Marie; Daru, Barnabas H.; Proffitt, Ed; Larkin, PatrickSeagrass meadows provide enormous ecosystem goods and services, ultimately establishing complex coastal habitats that support diverse collections of marine organisms. However, the future of seagrass communities under rapid shifts in climate in the Anthropocene—a period of pronounced human impact on biotic communities—has recently been questioned. Uncertainties from sampling biases present challenges to ecologists and evolutionary biologists in understanding species sensitivity to anthropogenic climate change. Here, we synthesize possible impediments that can constrain research to assess present and future seagrass responses to climate change. First, our knowledge of seagrass occurrence information is prevalent with biases, gaps and uncertainties that can influence inferences on species’ response to global change. Second, research on seagrass diversity has been focused on species-level metrics that can be measured with data from the present - but rarely accounting for the shared phylogenetic relationships and evolutionary distinctiveness of species. Third, compared to the mass production of species occurrence records, computational tools that can analyze these datasets in a reasonable amount of time are almost non-existent or do not scale well in terms of computer time and memory. These impediments mean that scientists must work with incomplete information and often unrepresentative data to predict how seagrass diversity might change in the future. In chapter one, we discuss these shortfalls and provide a framework for overcoming the impediments and diminishing the knowledge gaps they generate. Although climate change projections indicate significant threats to terrestrial biodiversity, shifts in species composition in marine environments might be equally profound. Here, we also explore how different facets of α-diversity (i.e., within all seagrass communities globally) and β-diversity (i.e., between seagrass communities) of seagrasses may respond to future climate change scenarios across the globe and compare them with the existing network of marine protected areas. By utilizing ensemble species distribution modeling under various scenarios of climate change, we observe widespread decreases in seagrass weighted endemism on a global scale. This projected loss in seagrass endemism will result in decreases in β-diversity within temperate regions resulting in the homogenization of seagrass communities in these regions. Regardless of the climate scenario, the hotspots and cold spots of these projected shifts in seagrass α- and β-diversity are predicted to occur outside the current network of marine protected areas, suggesting that these marine protected areas will be insufficient to safeguard the future of seagrasses. Our findings report species’ response for a group underrepresented in climate change assessments yet crucial in maintaining marine food chains.Item Behavior of popular indices of genetic diversity in simulated expanding populations(2022-05) Bynum, Adam; Bird, Christopher E.; Sterba-Boatwright, Blair; Portnoy, DavidProtecting genetic diversity is an integral component of food security, fishery management, and biodiversity conservation, and thus the ability to model and predict the distribution of genetic diversity is valuable. Population genetic theory predicts that genetic diversity will be greatest in the largest populations at mutation-drift equilibrium, implying that efforts to preserve diversity would be best focused on keeping populations as large as feasibly possible. Natural populations, however, are rarely in equilibrium, because their sizes can fluctuate due to a variety of processes, e.g., populations that have had a recent bottleneck or invaded a new habitat. To predict patterns of genetic diversity in natural populations, it has become increasingly important to understand how populations behave in non-equilibrium scenarios. Here we report the effects of mutation rate (µ), initial population size (Ne0), and final population size (Ne1) on the genetic diversity in expanding populations using a Wright-Fisher forward time model built with SLiM2. Using a 300 bp sequence to simulate modern genome-wide surveys of genetic variation (RAD), a range of naturally occurring mutation rates, and population sizes, multiple models were created to cover a broad portion of parameter space, and six commonly reported measures of genetic diversity estimated. As previously reported, genetic diversity increased with increasing population size given a similar set of circumstances, but there are broad swaths of parameter space where small populations exhibit greater diversity than large populations, making historical context critical in population genetics analysis. Depending on population size and mutation rate, the different diversity indices (nucleotide diversity, gene diversity, number of haplotypes, effective number of haplotypes, number of heterozygotes, and number of substitutions) progressed towards equilibrium at different rates. Furthermore, different diversity indices had different levels of sensitivity to changes in diversity at different times. To better describe the change in diversity with time, logistic growth models were used to estimate the equilibrium diversity (Deq), initial diversity value (D0), amount of time required to reach halfway to genetic equilibrium (t50eq), growth parameter (Φ3), maximum rate of genetic diversity increase (r), and time required to reach 95% of the equilibrium value (t95) in populations that expand from Ne0 to Ne1. We employed both linear and non-linear model fitting and used AIC to identify the best models describing the logistic growth parameters with varying Ne0, Ne1, and µ. In most cases, the models fit the simulated data well as the relative bias is low, ranging from +/- 3%, but the models did not perform as well when Ne0, Ne1, and µ, are small, with relative bias as high as 20%. The best models were used to create a tool that estimates the diversity of a population given the time since the onset of expansion, Ne0, Ne1, and µ. The prediction model performed best when using the Ne0, Ne1, and µ used in the simulations but could give misleading diversities when interpolating, so a switch was created to restrict the tool to only accept the predefined set of parameter values. This tool can be used to get a rough approximation of how long it will take for genetic diversity to accumulate and determine why there might be deviations from the neutral expectation that large populations have more diversity without running time consuming simulations and subsequent analysis.Item Behavioral condition of red drum Sciaenops ocellatus fingerlings exposed to habitat structures and predators in rearing ponds(2017-08) Schacht, Tyler Hans; Withers, Kim; Vega, Robert R.; Scarpa, John; Proffitt, CharlesStock enhancement programs strive to propagate fish similar to their wild counterparts, but hatchery-reared fish are often deficient in their ability to detect and avoid predation. The objective of this study was to determine if the provision of complexly structured habitat would improve post-stocking survival of hatchery-reared red drum, Sciaenops ocellatus, when exposed to free-roaming predators. Experiments were conducted in 0.2 ha rearing ponds between July and December 2016 at the Coastal Conservation Association Marine Development Center in Corpus Christi, Texas. Three habitat treatments (non-vegetated [normal rearing], artificial seagrass, and artificial seagrass with predator exclusion cages) were used to assess if habitat complexity influenced growth and condition. Fish growth (TL) was affected by trial (i.e., seasonality; P < 0.0001) but not by treatment (P = 0.178). After rearing to the fingerling stage (36 days post-hatch), survival from predation was assessed by exposing red drum to free-roaming predators (pinfish, Lagodon rhomboides) in experimental “wild” ponds (0.2 ha) with artificial seagrass for 24 hours. In two trials, fish condition (K) differed significantly among treatments (P<0.0001) and was lower in the artificial seagrass treatment with predator exclusion cages compared to the other treatments. Red drum may have been more active and vigilant (“leaner”) when exposed to caged predators, while the fish in the unstructured habitat led a more sedentary life (“fat”). Overall, when exposed to free-roaming predators in a “wild simulation” fish reared in ponds with the addition of structured, complex habitat survived better. The results of this study suggest that the provision of complexly structured habitat improved behavioral mechanisms (i.e., foraging, predator-avoidance) that may increase post-release survival of hatchery-reared red drum.Item Biological productivity associated with the serpulid reefs of Baffin Bay, Texas(1997-08) Hardegree, Beau; McKee, David A.; Prouty, Jennifer S.; Tunnell, John W.; Dunton, Kenneth H.The upper Laguna Madre and Baffin Bay-complex has long been noted for its abundant finfish populations despite its generally persistent hypersaline condition. The purpose of this present study was to determine the contribution of the serpulid worm reefs to the productivity of Baffin Bay. The primary focus of this thesis was to test the hypothesis that fish were larger and found in higher concentrations near the serpulid worm reefs in Baffin Bay, and to quantify the abundances of potential prey items associated with the reefs. In addition, I measured the productivity (by O2 evolution) of the epiphytic algae growing on the reefs and compared it to published seagrass studies in the upper Laguna Madre. Lastly, I examined the dependence of consumers on carbon fixed by these primary producers using stable carbon isotope ratios as tracers. A total of 5,396 individuals representing 35 fish species, were collected by trammel net during the study. Seven fish species (Mugil cephalus = 27.3 o/q Pogonias cromis = 20.2 %, Cynoscion nebulosus = 15.2 %, Leiostomus xanthurus = 12.1 %, Arius felis = 10.7 %, Lagodon rhomboides = 2.3 %, and Sciaenops ocel/atus = 1.1 %) comprised 89.0 % of the total catch. The overall ichythyofaunal catch rate was not significantly different between reef and non-reef sites and only a seasonal effect in the catch rate data was observed. Seasonal differences can be explained by the recruitment of fish into the bay in Spring and Summer. These seasonal peaks can be attributed to three species: Arius felis, Pogonias cromis, and Leiostomus xanthurus. No strong evidence was found to support the hypothesis that larger fish congregate around the serpulid worm reefs.Item Brevetoxin accumulation and persistence during a Karenia Brevis (Red Tide) bloom in South Texas(2016-12) Savicky, Jennifer Morgan; Zimba, Paul V.Red tide blooms composed of the harmful microalgae, Karenia brevis, are bi-annual events along the South Texas coast that cause marine and terrestrial animal mortalities. On September 13, 2015, a red tide bloom occurred from Port Aransas, TX to South Padre Island, TX and persisted in Corpus Christi Bay, TX until November 23, 2015. The objective of this study was to determine if brevetoxin (PbTx), produced by K. brevis, was passively or actively accumulated in macroalgae and if so, determine persistence time and depuration rates. Sargassum was collected from Padre Island National Seashore on September 26, 2016 and co-cultured with seawater containing K. brevis. Accumulation of PbTx was measured for a 72-hr exposure period. The PbTx concentration was determined using ELISA (reported as PbTx-3 equivalents) and confirmed by HPLC-MS/MS (normalized to PbTx-1 standard). The Sargassum community was partitioned mechanically to include epiphytic algae (with concentrations as high as 26 ng/mL PbTx-3 equivalents) and toxin adsorbed on Sargassum (up to 51 ng/mL PbTx-3 equivalents). Concentrations as high as 100 ng/g PbTx-3 (by ELISA) and 934 ng/g PbTx-1 (by HPLC-MS/MS) were detected in Sargassum tissue. As little information is available on PbTx in plant vectors; a second study assessed toxin depuration and persistence in macroalgae after the K. brevis bloom subsided. Ulva intestinalis was collected from Corpus Christi Bay on November 6, 2015 and incubated in f/10 media for a 30-day period to assess depuration. The epiphytic fraction contained over 17 ng/mL PbTx-3 equivalent and above 3 ng/g PbTx-3 equivalent in adsorbed PbTx over the 30-day period. U. intestinalis tissue PbTx concentration remained above 110 ng/g PbTx-3 equivalent. These results confirm that PbTx can be present in the macroalgal community for at least one month after a K. brevis bloom subsides. This study is the first to assess macroalgae as a vector for PbTx trophic transfer. Pelagic forms of macroalgae can accumulate and transfer PbTx into regions not experiencing red tides while toxin in attached forms can persist and be released to the environment after a bloom has disappeared. In future studies, examination of accumulation, depuration, and persistence of toxins in other macroalgal species should be considered. Studies on the transfer of marine algal toxins to different communities (i.e. beaches) could provide a better understanding of post-bloom effects.Item Cellular mechanisms of decision making in Aplysia californica(9/26/2014) Dickinson, Kathy Jan; Mozzachiodi, RiccardoAll animals are perpetually besieged with stimuli and face an extraordinary array of choices. We constantly must decide to which stimuli to respond, as well as how and when to respond. Although the decision-making process is a fundamental brain function, understanding the mechanisms that govern this function is made difficult by the complexity of the brains of most animals. To overcome this obstacle, we studied Aplysia californica, a marine mollusk with a simple nervous system, whose behaviors are controlled by a limited number of identified and identifiable neurons. Aplysia feeding behavior offers the opportunity to study decision making at both the behavioral and cellular levels. Feeding behavior in Aplysia is critical for its survival and relies on characterized cells within the feeding neural circuit, which are amenable for cellular analysis. Aplysia exhibits biting movements to ingest food and, when food satiated, decides not to bite in the presence of food for a prolonged period of time (≥ 24 h; e.g., Kupfermann 1974a,b). Neuron B51, within the feeding neural circuit, exhibits decision-making characteristics, in that its all-or-nothing burst of activity biases the feeding neural circuit toward producing the motor patterns responsible for biting behavior (Nargeot et al. 1999; Brembs et al. 2002; Mozzachiodi et al. 2008). The goal of this study was to determine whether B51 is a site of plasticity underlying the decision not to bite following food satiation. The first objective of this study was to test the hypothesis that the satiation-induced decision not to bite is accompanied by a reduction in the activity of B51. Pairs of animals were used for each experiment, one experimental animal fed to satiation and one control animal kept unfed. The animal receiving satiation treatment was fed strips of seaweed until it decided to no longer bite in the presence of food. The effects of satiation on feeding behavior were analyzed using a seaweed extract to measure the number of bites. Seaweed extract was used to provide a constant food stimulus to elicit bites. Bites were measured before (pre-test) and 24 h after (post-test) treatment (satiation/control) to establish whether treatment caused any change in biting. The satiated group exhibited a significant decrease in the number of bites compared to the control group 24 h after treatment, which indicates the decision not to bite following food satiation was made in the satiated group. Cellular analysis of neuron B51 in satiated and control animals was possible because the effects of satiation persisted for 24 h. After the post-test, the buccal ganglia of satiated and control animals were isolated in vitro and B51 properties (resting membrane potential, input resistance and burst threshold) were measured. The satiated group exhibited a significantly higher burst threshold compared to the control group. B51 increase in burst threshold is indicative of a decrease in excitability, which is the function that enables neurons to generate action potentials in response to stimuli and is consistent with the suppression of feeding following satiation. No differences were observed in resting membrane potential or input resistance, which indicates that the decrease in B51 excitability induced by satiation treatment is intrinsic to the neuron. The second objective was to test the hypothesis that satiation-induced decreased excitability in B51 would no longer be observed at the time point in which biting resumed. Biting was no longer suppressed at 96 h following satiation (i.e., there was no significant difference in biting behavior between satiated and control animals). Notably, B51 excitability was not different between satiated and control animals 96 h after treatment. The experiments conducted addressed the function of decision making. We examined the cellular changes in the decision-making properties of neuron B51 following food satiation whereby the behavior controlled by this neuron is suppressed. In summary, these findings indicate that B51 is a site of plasticity underlying the decision not to bite following food satiation in Aplysia.Item Changes in arthropod communities as Avicennia germinans expands into Gulf of Mexico salt marshes(2017-05) Loveless, Jacob; Smee, Delbert Lee; Withers, Kim; Patrick, ChristopherClimate change is driving poleward shifts in species distributions worldwide. In the Gulf of Mexico (GOM), warming temperatures are allowing cold sensitive black mangroves (Avicennia germinans) to move north into coastal wetlands that have previously been dominated by the marsh grass Spartina alterniflora. Avicennia germinans in the western GOM become established in upper tidal elevations, creating dense monocultures and replacing S. alterniflora and other wetland plants (e.g., Salicornia virginica, Batis maritima). I investigated insect community assemblages in wetlands with and without A. germinans to assess potential effects of A. germinans expansion on insect fauna. Insect abundance, biomass, richness, diversity, and community and feeding guild composition were measured in both the spring and the fall across varying levels of A. germinans abundance and at low and high tidal elevations. Insects were more abundant and had larger biomass contributions in both the spring and the fall in upper tidal elevation wetlands where A. germinanss have yet to become established. Richness and diversity were not different in any of the wetland types or tidal elevations, however multivariate analysis indicated significant differences in community structure in the wetlands without A. germinans. Feeding guild composition was also different; wetlands containing A. germinans monocultures had less predator biomass. Thus, shifting vegetation brought on by climate change can alter insect communities in coastal wetlands, illustrating the need for a more comprehensive understanding of climate change effects on fauna in response to shifting foundation species.Item Characterizing marine subsurface fungi from oligotrophic South Pacific Gyre sediments(2018-08) Sobol, Morgan Starr; Reese, Brandi Kiel; Turner, Jeffrey W.; Gonzales, Xavier FonzFungal communities from the deep marine subsurface may be important in global biogeochemical cycles through remineralization of sedimentary organic matter, but this has not yet been thoroughly observed. This study analyzes the fungal role in subsurface biogeochemical cycles and understands how these organisms have adapted to extreme environments, such as the nutrient and organic matter depleted sediments of the South Pacific Gyre. Sediment cores were collected during the Integrated Ocean Drilling Program Expedition 329 to the South Pacific Gyre on board the D/V JOIDES Resolution in the Fall of 2010. Two fungal isolates were cultured from 70 million year old sediments. Previous analysis found that the two isolates were closely related to Penicillium species. To fully characterize the isolates and test their physiological boundaries, we grew them at different temperatures, salinities and pH. Whole genomic analysis was used to understand the fungi’s physiology and metabolism on a molecular level. The fungi were found to prefer growth at mesophilic temperatures and low NaCl concentrations. Growth occurred between pH 3 and pH 8. The isolate from 12 mbsf grew optimally from pH 3 to pH 8 and the isolate from 124 mbsf grew optimally from pH 3 to pH 6. Fermentation of lactose and sucrose was confirmed, but not nitrate and sulfate reduction. The fungal isolates from the South Pacific Gyre sediment had physiological capabilities that were consistent with the in situ subsurface conditions and contained genes that were capable of utilizing the recalcitrant carbon sources found in situ. The results from this study expand on the fungal limits of life and highlight their important role global carbon cycle.Item Characterizing the unfished oyster reef community of Sabine Lake Estuary relative to surrounding marsh edge and nonvegetated bottom habitats.(8/8/2013) Nevins, Jaimie; Pollack, Jennifer BeseresSabine Lake is an approximately 360 km2 estuary on the Texas-Louisiana border formed by the union of the Neches and Sabine Rivers. The estuary is unique in terms of its large oyster reef complex with no record of commercial harvest as far back as the 1960’s. However, after substantial oyster mortalities in Louisiana estuaries due to hurricane activity and freshwater releases post-Macondo oil spill, Louisiana has shown strong interest in opening their portion of Sabine Lake to supplement lost commercial harvest. The overarching goal of this research project was to describe oyster population structure and community composition of finfishes and invertebrates on this naturally functioning reef system compared to nearby nonvegetated bottom and marsh edge habitats. Live and dead oyster abundances were significantly different among seasons, with spring 2013 having the highest live oyster abundance, and fall 2011 having the highest dead oyster abundance. Approximately half (45%) of all live oyster heights measured were ≥ 80 mm, while the largest recorded height was 203 mm in spring 2013. The high abundance of large oysters collected within Sabine Lake Estuary may offer unique ecosystem services compared to commercially fished reefs with low, or scattered vertical relief. Oyster reef and nonvegetated deep (> 3m) habitats had significantly lower total faunal densities than the marsh edge habitat throughout all seasons. The highest species diversity and richness were observed in the nonvegetated deep habitat, while the oyster reef habitat had a higher diversity than both marsh edge and shallow nonvegetated habitats. The highest abundances of dominant crustaceans, transient, and resident fishes were found within the marsh edge habitat. Despite observing lower densities of organisms, our community analysis provides evidence that the oyster reef habitats support a unique community of fishes and crustaceans compared to the marsh edge and nonvegetated habitats. Characterizing and understanding the true value of the unfished oyster reef, marsh edge, and nonvegetated habitats will enhance natural resource management decisions in the future, by incorporating potential effects due to commercial fishing activities.Item Cloning, sequencing and analysis of housekeeping genes towards the development of molecular stress response markers in seagrasses(4/11/2012) Dovalina, Stephanie; Cammarata, KirkSeagrass meadows are important primary producers and habitats in estuaries and near-shore marine environments, but many populations are in decline due to anthropogenic influences. Measurements of biomass are commonly used to gauge the physiological status of seagrass meadows, but these are "lagging indicators" of the underlying causal event(s) and have not fully answered questions about why, despite attempts to correlate with environmental conditions. The goal is to develop a method for transcriptomic measurements to compare relative long-term stress response levels between impacted and nonimpacted seagrasses. Given the lack of genomic information for seagrasses in the western Gulf of Mexico, it was first necessary to obtain seagrass genomic sequences based on knowledge of model systems. Control (Act1, Gapdh) and stress genes (Apx1, non-symbiotic Hb1, and Pal1) were first identified by literature search using the rice (Oryza sativa) genome as a model. Multiple alignments were performed to identify conserved regions and design degenerate PCR primers used for cloning and sequencing from five seagrass species: Halodule beaudettei (synonymous with H. wrightii, Cymodoceaceae), Cymodocea filiformis (Cymodoceaceae), Thalassia testudinum (Hydrocharitaceae), Halophila engelmannii (Hydrocharitaceae), and Ruppia maritima (Ruppiaceae). Amplification of the desired stress-related genes from seagrasses was unsuccessful. Hb1 primers yielded PCR products from H. beaudettei around the expected size (~759 bp), but sequence analysis identified this as a bacterial-like NAD/NADP octopine/nopaline dehydrogenase. Using genomic DNA, actin gene fragments (1-1.8 kb) corresponding to exons 2-4 were amplified from five species, and Gapdh (exons 5-9) was amplified from H. beaudettei. Intron length varied for actin with C. filiformis containing the largest introns. Splicing junctions were verified comparing cDNA sequences from H. beaudettei. Actin and GAPDH sequences were aligned in MEGA using MUSCLE and compared with other plant sequences in GenBank®. A phylogenetic tree was constructed for each gene using Maximum Likelihood with 1,000 bootstrap replicates. Actin cDNA sequences from the same families grouped together to form clades reaffirming phylogeny. However, the genomic sequences of H. beaudettei actin, as well as GAPDH, did not group together with the expected clade, unlike the cDNA sequences from the same species. The genomic actin sequences were most closely related to rice Act1, which is grouped with reproductive actins in other plants. Similarly, the genomic sequences of GAPDH did not group together with the mRNA sequences, but instead grouped with dicots reaffirming BLAST search results. Mean codon bias differences in genomic sequences vs. cDNA along with differences in theoretical isoeletric points seem to indicate multiple members of gene families for actin and GAPDH in H. beaudettei, similar to previous work in all angiosperms studied thus far. This finding suggests that the genomic vs. cDNA clones of both actin and GAPDH may represent differentially expressed paralogs. This work raises the interesting possibility that expression patterns of individual housekeeping paralogs could be used as stress indicators. Future work should include high-throughput sequencing to analyze expressed housekeeping genes under a variety of environmental conditions and to identify stress-related gene candidates in the transcriptome.Item A Comparison of Outdoor Mixed Cultures Versus Monocultures of Nannochloropsis salina and Phaeodactylum tricornutum for Biofuel Application(2017-05) Konkle, Brooke; Siccardi, Anthony; Scarpa, John; Wetz, Michael S.Microalgae have been identified as a potential chemical source for biofuels, but production costs still greatly limit this industry. The purpose of this study was to determine the efficiency of mixed algal cultures containing two species of microalgae, Nannochloropsis salina and Phaeodactylum tricornutum, in comparison to their respective monocultures. The respective microalgae cultures were grown in 557L experimental tanks with harvests performed every 3-7 days, i.e., after growth had reached the stationary phase, for a period of 90 days. Microalgae biomass (g/m2), productivity (g/m2/day), and nutrient utilization were analyzed with respect to treatment and different temperatures. The average biomass of the mixed culture treatment (39.81 g/m2) was significantly (p=1.04 x 10-5) greater compared to the P. tricornutum monoculture treatment (35.57 g/m2) but was not significantly different from the N. salina monoculture treatment (39.4 g/m2). Observations of biological contamination do not support the hypothesis that contamination would be less in mixed cultures, as this treatment experienced the highest average contamination levels.Item Comparison of phytoplankton biomass and community composition in three Texas estuaries differing in freshwater inflow regime(2020-08) Chin, Tiffany; Wetz, Michael; Antoinetta, Quigg; Roelke, DanielPhytoplankton are at the base of the marine food web and are sensitive indicators of environmental change, such as changes to freshwater inflow in estuaries. Because freshwater inflows to Texas estuaries are projected to decrease in the coming decades as a result of increasing human freshwater demands and climate change, it is critical to understand ecosystemlevel responses to freshwater inflow variability. This study examined phytoplankton community composition and biomass, along with relationships to environmental variables in three Texas estuaries with differing freshwater inflow regimes. The estuaries were San Antonio Bay (highest inflow levels), Nueces-Corpus Christi Bay (intermediate inflow levels), and Baffin Bay (lowest inflow levels). The goal was to understand the impacts of freshwater inflow variability and magnitude on phytoplankton dynamics. Baffin Bay had the highest phytoplankton biovolume, followed by NC and SA. Higher frequency and magnitude inflows in SA corresponded to overall lower biovolume and shifts of biovolume maxima downstream, while infrequent inflows in BB were followed by a sustained diatom bloom. Inflows to NC affected only the upper estuary, while the lower estuary appeared to be more influenced by ocean exchange. Large, fastergrowing taxa, such as Rhizosolenia, were observed in greatest abundances in Baffin Bay, while slower-growing dinoflagellates dominated in NC and SA. Findings of lower biovolume and higher proportion of slow growing taxa in the high inflow estuary, SA, are contrary to our understanding based on the available literature and underscore the importance of understanding system-specific drivers for effective coastal management.