No description available.

No description available.

As climate change threatens with sea-level rise and more storms, increased erosion could increase the need for beach nourishment. Alterations to sand characteristics may result in changes to the sea turtle nest microenvironment, impacting the temperature and oxygen levels which may affect hatchling performance. In this study, leatherback, loggerhead, and green nests were sampled from two sites with different sand characteristics in Juno Beach, Florida, USA. Gas exchange was higher in green turtle nests with a greater mixture of sediment. Darker sediment elevated nest temperatures. Finer sediment and a greater mixture of sediment in leatherback nests elevated the nest temperatures; conversely finer sediment, and a greater mixture of sediment decreased loggerhead and green nest temperatures. Elevated nest temperatures reduced leatherback, loggerhead, and green turtle hatchling performance. Understanding the relationships between beach composition, nest environment, and hatchling performance will aid management decisions essential to sea turtle conservation. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2020. / FAU Electronic Theses and Dissertations Collection

High-latitude reefs have been postulated as refugia, centers for resilience or the first areas to undergo re-organization under climate change. The Southeast Florida Reef Tract (SEFRT) is a high-latitude reef system (>25 °N) running parallel to the highly urbanized coastline of southeast Florida. With a benthic community comprised of a mixture of coral reef associated assemblages, the SEFRT is towards the northern limit of stony coral cover due to temperature constraints. This study analyzed spatial variations in benthic cover, spatiotemporal changes in the benthic community and the impact of spatial and temporal fluctuations in temperature on benthic cover on the SEFRT, from 2007-2016. Photographic data from two long term monitoring projects was used to calculate the percent cover of taxonomic assemblages in the benthic community. In situ temperature data and modelled data from HYCOM were used in combination to assess the impact of temperature fluctuations and thermal stress events. Data was split on a latitudinal gradient into six defined ecosystem regions based on biogeographic boundaries and at major port channels. These accounted for any possible range expansion and spatiotemporal variations on the SEFRT. Statistical analysis via generalized linear models (GLM) identified significant changes in the major benthic taxa, stony coral, octocoral, sponges and macroalgae. Ecosystem regions showed strong clustering by their taxonomic composition and this was in part created by temperature variation. Stony coral cover significantly declined on the SEFRT and a concomitant significant increase in macroalgae cover may create a negative feedback loop which hinders recovery. Spatiotemporal variations in benthic cover were found between ecosystem regions and thermal stress events, both hot and cold, had immediate and latent impacts on benthic cover. This has resulted in biotic homogenization on the SEFRT with a retraction of outlier regions towards the mean. Anthropogenically influenced high-latitude reefs are significantly impacted by thermal stress. As oceans continue to warm, populations expand, coastlines continue to develop and pollutants persist, the benefits of potential thermal refugia are negated.

Channel catfish (Ictalurus punctatus) have a broad distribution from Canada to Mexico, suggesting that different strains may have different thermal tolerances. In aquaculture, daily temperature maximums up to 36-40°C and fluctuations of 3-6°C occur, and may be exacerbated by future climate change. To quantify differences in thermal tolerance amongst geographically-distinct channel catfish strains and corresponding hybrid catfish (I. punctatus x [blue catfish] I. furcatus): acute critical thermal maximum (CTmax), and the effects of chronic thermal regimes on growth, survival and differential gene expression were examined. Southern channel catfish had higher CTmax than northern, and channel catfish had higher CTmax than hybrid catfish. Under chronic thermal stress, hybrid catfish had the greatest survival and most consistent growth. Further, northern channel catfish had the greatest magnitude and largest amount of upregulated gene transcripts in response to high temperatures, indicating greater thermal stress. Therefore, catfish thermal tolerance varies by geographic region and species.

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Intertidal habitats are characterized by dynamic, tidally-driven fluctuations in abiotic and biotic factors. Many of the environmental stressors that vary across the intertidal (e.g., temperature, oxygen, food availability, predation pressure) are strong drivers of metabolic rate in ectotherms. As such, we predicted that there may be pronounced differences in the metabolic and stress physiology of conspecific sessile invertebrates occupying at different relative tidal heights. The common acorn barnacle Balanus glandula represents an ideal model organism in which to investigate the possibility of tidal height-dependent physiological differences, owing to their wide distribution in the intertidal zone and their eurytolerant nature. In the first chapter of my thesis, we investigate the hypothesis that B. glandula anchored in the low intertidal have a greater capacity for anaerobic metabolism than conspecifics in the high intertidal, and that this is due to increased predation pressure during submersion. Further, we explore the temporal and spatial fidelity of certain tidal-height driven trends in lactate dehydrogenase activity previously observed in our lab (i.e., higher LDH activity in low intertidal barnacles; Horn et al., 2021), and attempt to identify environmental variables that drive plasticity in LDH activity. We found that, in general, there were higher densities of B. glandula and gastropod whelk predators in the low intertidal compared to the high intertidal, but follow-up studies in the lab revealed that opercular closure in B. glandula was induced by predator exposure (Acanthinucella spirata) for less than 24h. This time frame for shell closure is unlikely to result in internal hypoxia or enhance capacity for anaerobic metabolism. We were therefore not surprised to find that LDH activity in B. glandula was likewise not affected by predator exposures (48h) carried out in the lab. After failing to find an effect of predators on LDH activity in B. glandula, we attempted to replicate the previous finding that LDH activity was highest in low intertidal populations of B. glandula. We did this at the original location in San Luis Obispo Bay, CA as well as at three novel field sites and across seasons and years. While we did observe variation in LDH activity over time and between sites, we did not consistently observe the same trend in LDH activity whereby low intertidal barnacles had the highest activity. In response to these variable patterns, we attempted to identify what environmental parameters, other than predation, might be responsible for plasticity in LDH activity. Unfortunately, neither temperature nor emersion stress – the two variables we examined – had any significant an effect on LDH activity in B. glandula. These data suggest that there must be multiple, interacting stressors – including tidal position - that influence the anaerobic metabolic capacity of B. glandula. In the second chapter of my thesis, we went on to investigate how the response to thermal stress might differ between populations of B. glandula from different vertical heights in the intertidal zone. To this end, we assessed how aerial temperature stress affected oxygen consumption rates (MO2), superoxide dismutase (SOD) activity, and time to mortality in B. glandula collected from both low and high intertidal positions. We found that barnacles from the low intertidal showed a significant increase in MO2 with higher temperature, while MO2 was unaffected by temperature in B. glandula from the high intertidal. We also observed that SOD activity levels were higher in the high intertidal barnacles compared to the low intertidal barnacles, although neither group was increasing SOD activity under higher temperature. Finally, we observed significantly longer survival times during thermal stress in barnacles from the high intertidal zone (e.g., LT50 = 8.75 h vs 5 h at 33˚C for the high and low barnacles, respectively), although this advantage seemed to be lost with the addition of desiccation stress at these same temperatures. It is evident that life in highest reaches of the intertidal zones is physiologically challenging, and this has resulted in a population of B, glandula barnacles that are less sensitive to and better suited to tolerate temperature extremes than conspecifics in the lowest intertidal regions. Understanding how habitat variation may differentially impact the metabolic and thermal stress physiology of B. glandula is increasingly important as climate change progresses. This is particularly significant considering that organisms in the intertidal already reside within a relatively stressful environment and may be living closer to their thermal tolerance limits than animals from less extreme habitats.

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Due to the fact that bone cells are highly responsive to mechanical stimuli, shear stress has been extensively studied for its ability to enhance osteogenic differentiation through mechanotransduction. In addition, thermal stress has also been explored as a conditioning method to stimulate cellular proliferation, differentiation, and cytoprotection through heat shock protein induction. Despite the beneficial effects observed with individual stress on cells, there has been little focus on the potential of a combination of stresses to improve cellular response. Therefore, the aim of this study was to investigate the effect of combined shear and thermal stress on preosteoblasts to stimulate an enhanced osteogenic response. To achieve this, MC3T3-E1 cells were exposed to one of the following protocols for an hour: no stress (control), shear stress at 1 dyne/cm2 using a parallel plate flow chamber, thermal stress in a 42°C incubator, or combined shear and thermal stress (1 dyne/cm2 at 42°C). Stress treatments were applied on Day 2, Day 6, and Day 10. To assess the early response of cells to stress treatments, we measured metabolic activity, expression of signaling factors, and HSPs following stress on Day 2. Despite an initial decrease in metabolism, combined stress stimulated a strong response in VEGF (12.49 RFI) COX-2 (12.32 RFI), HSPs (2-4 RFI) and increased PGE accumulation. The long-term cellular response to stress treatments was measured on Day 15 by evaluating the ability of combined stress to stimulate late stage markers of differentiation. Combined stress increased OPN gene and protein expression, yet OCN was minimally affected by stress treatments. However, mineralization was significantly decreased with combined stress. Overall, combined stress was able to stimulate an enhanced effect across a majority of the bone-related markers measured, whereas individual shear stress or thermal stress were limited in their response. This suggests that combined stress can provide the appropriate cues to modify osteoblast differentiation and generate an enhanced osteogenic response. / Master of Science

The effect of thermal cycling on the state of stress in polymeric materials bonded to stiff elastic substrates was investigated using numerical techniques, including finite element methods. The work explored the relationship between a cyclic temperature environment, temperature-dependent viscoelastic behavior of polymers, and thermal stresses induced in a constrained system. Due to the complexity of developing a closed-form solution for a system with time, temperature, material properties, and boundary conditions all coupled, numerical techniques were used to acquire approximate solutions. Descriptions of attempted experimental verification are also included. The results of the numerical work indicate that residual stresses in an elastic-viscoelastic bimaterial system incrementally shift over time when subjected to thermal cycling. Tensile axial and peel stresses develop over a long period of time as a result of viscoelastic response to thermal stresses induced in the polymeric layer. The applied strain energy release rate at the crack tip of layered specimens is shown to similarly increase. The rate of change of the stress state is dependent upon the thermal cycling profile and the adhesive’s thermo-mechanical response. Discussion of the results focuses on the probability that the incrementing tensile residual stresses induced in an adhesive bond subjected by thermal cycling may lead to damage and debonding, thus reducing durability. / Master of Science