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Functionality of Cnidarian symbiosis with Symbiodiniaceae is fundamental to reef ecosystem success. Symbiodiniaceae cells have a complex life history, which, in hospite, is controlled by the host. In addition to the endosymbiotic lifestyle, they can exist free-living cells which diurnally alternate between a coccoid, vegetative night-time form to a day-time motile, flagellated cell. Their cell division cycle is gated by external light cues, and correlates with transitions in cell morphology. In contrast, endosymbiotic cells have an elongated G1 phase – demonstrating a de-coupling of cell cycle from 24-hour cycle in response to symbiosis. Furthermore, daughters of dividing endosymbiotic Symbiodiniaceae remain as coccoid cells, de-coupling morphological and cell division cycles. How this occurs remains unknown. The answer may lie in crystalline uric acid deposits, which are present only in motile, daytime cells, correlating with G1 and S phase. These store excess nitrogen and are quickly metabolized in low nitrogen availability. They also function as an eyespot. The influence of uric acid on the life cycle of free-living and endosymbiotic Symbiodiniaceae is unknown. In this study, I treated cultures of B. minutum with allopurinol, an inhibitor of uric acid synthesis. Flow cytometry showed that allopurinol the reduced growth rate and ratio of coccoid:motile cell cultures. RNA sequencing and differential gene expression analysis identified biological processes enriched in allopurinol treatment. I hypothesize that an intracellular lack of nitrogen imposed lack of uric acid crystals stimulates the General Amino Acid Control pathway. This represses translation, explaining the downregulation of ribosomal proteins, and upregulates amino acid and purine de novo biosynthesis pathways. Repression of translation may slow cellular growth and the G1 phase of the cell cycle, reducing number of cells meeting the size threshold for G1/S transition. Without uric acid deposits, cells may lack a functioning eyespot and not receive light cues which usually trigger morphological transitioning. This may suppress the motile morphology of free-living Symbiodiniaceae and cells in hospite even though the cell division cycle progresses, albeit more slowly. Genes involved in biosynthesis of flagella, thecal plates and the eyespot are upregulated, suggesting suppression of the motile form may act downstream of transcription.

Both global and local chronic environmental stressors associated with climate change and anthropogenic sources are increasing in severity, and can compromise the resilience of key marine ecosystems such as foundational coral reefs. Despite the impacts, however, there are major knowledge gaps in our understanding of direct interactive and compounding effects of multiple chronic environmental stressors on coral animals. Further, chronic stress may have sublethal, downstream impacts; for example, inhibiting the recognition and response to sudden acute stressors in the marine environment. The goal of this study was to determine the direct impacts of multiple chronic environmental stressors - elevated temperature (global), microplastic pollution, light availability, and food availability (local) - on survival and physiological performance of the emerging temperature coral model Astrangia poculata, and to determine how exposure to different chronic stressors affects their ability to deal with sudden acute stress. To achieve this, we exposed individual coral polyps to different combinations of stressors, and quantified the response of the coral host (growth) and symbiont (photosynthetic efficiency, chlorophyll a density). Coral polyps were then challenged with an acute stress near the onset, midpoint, and end of the experiment to quantify the impact of chronic environmental stress on the ability to mount a response to an acute stress. We found that the local stress of microplastic exposure had no impact on lethal or sublethal measures of the coral holobiont, while light was beneficial in maintaining coral mass. In contrast, elevated temperatures (representing global stress) reduced survival, diminished host and symbiont performance, and repressed the coral metabolic response under acute stress challenge. Feeding, however, was beneficial in preserving symbiont function, but has consequences for fitness and coral growth when presented with thermal stress, lending support to the growing hypothesis that this established mutualism shifts towards parasitism in stressful environmental conditions. Despite the magnitude of these combined stressors, over 80% of coral polyps survived, highlighting the overall resilience of A. poculata to diverse environmental challenges. These findings underline the complexity with which anthropogenic stressors interact to affect coral survivorship and resilience to future global change.

<p> Colonies of the soft coral Sinularia polydactyla collected from the vicinity of Panjang island, Jepara region, Central Java, Indonesia were tested to examine their antibacterial properties. </p> <p> Chemical analysis and bioassay-directed purification by repetitive column chromatography using Vibrio harveyi as tester strain revealed that S. polydactyla possesses antibacterial properties against this test strain. Purification gives a mixture of esters, which inhibited the growth of the marine biofilm forming bacterium, V. harveyi with an EC50 value of 0.075 mg/10 mL of culture medium. </p> <p> Chemical synthesis of the esters Hexadecyl palmitate (1 ), hexadecyl stearate (2), octadecyl palmitate (3), and octadecyl stearate (4) was accomplished from the alcohols and fatty acid acyl halides. Each purified ester was characterized by NMR and MS. Comparison of the MS for these authentic synthetic samples with that for the biologically derived sample showed that the latter was composed predominantly of esters 1 and 3. The individual esters were tested against V. harveyi. Compound 1 was active and 4 was less active, while 2 and 3 were inactive. Hence, 1 is the major active compound against V. harveyi in the natural mixture. </p> / Thesis / Master of Science (MSc)

<p> Primnoa resedaeformis is a deep-sea gorgonian coral with worldwide distribution and a lifespan of at least several hundred years. Recent work has suggested that it may be possible to obtain extended, high-resolution records of ambient oceanographic conditions from Primnoa skeletons. This thesis focuses on specimens recently collected live from the Northeast Channel, SW of Nova Scotia, from depths of 300-500m. </p> <p> Skeletal microstructure was examined as a prerequisite to geochemical sampling. Skeletons exhibit periodic growth at three distinct scales. Concentric annual rings throughout the skeleton, and sub-annual laminae in the horny axis, measure 200 +1-100 microns and 15 +1-10 microns, respectively. Fine-scale striae in the outer calcite cortex measure 1.5 +1-2 microns. The dark, gorgonin-rich portion of annual rings in the horny axis forms in winter, when currents in the NE Channel are most energetic. Growth in these animals is apparently tied to the passage of currents at seasonal, lunar and tidal frequencies. Annual ring widths in the horny axis could not be successfully cross-dated, however, a prominent dark ring that appears to have been formed in 1976 is present in several of the colonies examined. Prominent dark rings may serve as useful benchmarks in sclerochronology. </p> <p> Mg/Ca and Sr/Ca were measured by laser ablation ICP-MS in the predominantly calcite axial cortex. Across a 1.5°C gradient, Mg/Ca is positively related to temperature. Sr/Ca also increases with temperature, but this may be explained by the influence of Mg/Ca on Sr partitioning, rather than temperature. Near annual-resolution timeseries profiles of Mg/Ca are consistent within and among colonies having different growth rates. Conversion of Mg/Ca profiles to temperatures using a provisional calibration [Mg/Ca (mmollmol) = 4.88(+/-1.09) T (°C) + 70.92 (+/-6.79)] yields a range of values and trends that are consistent with the observational data. Mg/Ca in Primnoa, therefore, is a viable means of monitoring bottom-water temperatures. The North Atlantic Oscillation (NAO) is responsible for a significant component of inter-annual temperature variability in the Scotia-Maine region. Mg/Ca records from older corals could therefore provide extended proxy records of the NAO. </p> / Thesis / Master of Science (MSc)

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No description available.