Dissertations / Theses on the topic 'Coral bleaching'
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Graham, Nicholas. "Effects of coral bleaching on coral reef fish assemblages." Thesis, University of Newcastle Upon Tyne, 2008. http://hdl.handle.net/10443/128.
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Coral reefs have emerged as one of the ecosystems most vulnerable to climate variation and change. While the contribution of climate warming to the loss of live coral cover has been well documented, the associated effects on fish have not. Such information is important as coral reef fish assemblages provide critical contributions to ecosystem function and services. This thesis assesses the medium to long term impacts of coral loss on fish assemblages in the western Indian Ocean. Feeding observations of corallivorous butterflyfish demonstrates that considerable feeding plasticity occurs among habitat types, but strong relationships exist between degree of specialisation and declines in abundance following coral loss. Furthermore, obligate corallivores are lost fairly rapidly following decline in coral cover, whereas facultative corallivores are sustained until the structure of the dead coral begins to erode. Surveys of benthic and fish assemblages in Mauritius spanning 11 years highlight small changes in both benthos and fish through time, but strong spatial trends associated with dredging and inter-specific competition. In Seychelles, although there was little change in biomass of fishery target species above size of first capture, size spectra analysis of the entire assemblage revealed a loss of smaller individuals (<30cm) and an increase in the larger individuals (>45cm). This represents a lag effect where fishery production cannot be assured for the long term. A targeted before (mid-1990s) – after (2005) sampling program of coral reef benthos and fish assemblages in 7 countries across the Indian Ocean demonstrated changes in size structure, diversity and trophic composition of the reef fish community have followed coral declines in both fished and protected areas. The thesis highlights the pivotal role that loss of reef structural complexity plays in the effects of bleaching on fish assemblages and that coral reef management needs to radically adapt to address climate change issues.
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Hill, Ross. "Coral bleaching : photosynthetic impacts on symbiotic dinoflagellates /." Electronic version, 2008. http://hdl.handle.net/2100/526.
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University of Technology, Sydney. Faculty of Science.Global climate change is leading to the rise of ocean temperatures and is triggering mass coral bleaching events on reefs around the world. This involves the expulsion of the symbiotic dinoflagellate algae, known as zooxanthellae, from the coral host. Coral bleaching is believed to occur as a result of damage to the photosynthetic apparatus of these symbionts, although the specific site of initial impact is yet to be conclusively resolved. This thesis examined a number of sites within the light reactions of photosynthesis and evaluated the efficiency of photoprotective heat dissipating pathways. Upon expulsion, the capacity for long-term survivorship of expelled zooxanthellae in the water column was also assessed. A reduction in photosystem II (PSII) photochemical efficiency during exposure to elevated temperature and high light (bleaching conditions) was found to be highly dependent upon the increase in abundance of QB non-reducing PSII centres (inactive PSII centres), indicating damage to the site of the secondary electron acceptor, QB, resulting in a limited capacity for its reduction. Therefore, this reduced the rate of the reoxidation of the primary electron acceptor, QA-. Fast induction curve (FIC) analysis of the rise from minimum fluorescence to maximum fluorescence revealed a lower amplitude in the J step along this curve, which was consistent with a reduction in the rate of QA reoxidation. This photoinhibition of PSII was found to occur once the effectiveness of excess energy dissipation through energy-dependent quenching and state-transition quenching was exceeded, suggesting that these mechanisms were incapable of preventing photodamage. Antenna size heterogeneity showed little change under bleaching conditions with a significant increase in PSIIbeta only apparent in one species of coral. The thermostability of the oxygen evolving complex (OEC) and thylakoid membrane were found to increase during exposure to bleaching conditions and exceeded bleaching thresholds of corals. This rapid rise in temperature-dependent thermostability also occurred over seasons, where variation in ocean temperatures was matched by gradual shifts in OEC and thylakoid membrane thermotolerance. Variation in thermostability between species was not found to be linked to zooxanthellae genotype, and instead was related to the bleaching susceptibility of the host. Despite this capacity for resilience to bleaching conditions, the PSII reaction centres did not exhibit such a mechanism for rapid acclimatisation. Corals can only be as tolerant to bleaching conditions as their most sensitive component allows. The formation of nonfunctional PSII centres is therefore suggested to be involved in the initial photochemical damage to zooxanthellae which leads to a bleaching response. Zooxanthellae were found to be expelled irrespective of OEC function and thylakoid membrane integrity, as these sites of the photosynthetic apparatus were still intact when cells were collected from the water column. Although zooxanthellae were photosynthetically competent and morphologically intact upon expulsion, their longevity in the water column was dependent on the time of expulsion following the onset of bleaching and the ambient water temperatures. The survivorship of these zooxanthellae was restricted to a maximum of 5 days in the water column which suggests that unless expelled zooxanthellae inhabit other environs of coral reefs which may be more favourable for survival, their capacity for persistence in the environment is extremely limited. Chlorophyll a fluorescence measurements are a common tool for investigating photosynthetic impacts to in hospite zooxanthellae of corals. Pathways causing dark-reduction of the plastoquinone pool are shown to be active in corals and affect measurements which require dark-adaptation. Pre-exposure to far-red light was found to be an effective procedure to oxidise the inter-system electron transport chain and ensure determination of the true maximum quantum yield of PSII and accurate FICs. It is concluded that the trigger for coral bleaching lies in the photosynthetic apparatus of zooxanthellae and evidence is presented in support of this impact site not being the OEC or thylakoid membrane.
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Klaus, Rebecca. "Coral bleaching indices in theory and in practice : a comparative assessment of the 1997/98 Indian Ocean coral bleaching event." Thesis, University of Warwick, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.408231.
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Harikishun, Ameil. "Coral bleaching responses in Sodwana Bay, South Africa." Bachelor's thesis, University of Cape Town, 2013. http://hdl.handle.net/11427/7640.
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This study assessed the bleaching response (BR) of coral colonies within the central reef complex in Sodwana Bay, South Africa. Bleach surveys were conducted at 16 sites on 8 reefs over the period of 2007 to 2013. A total of 12 858 coral colonies from 30 taxa were randomly sampled and colonies were placed into 7 categories of bleaching response. This allowed for the calculation of taxon-specific BR as a weighted percentage of coral cover bleached. Continuous temperature records from a permanent temperature gauge on Two Mile Reef were used to assess thermal stress over this period. The percentage of coral colonies that bleached in 2007, 2008, 2011, 2012 and 2013 were 37.4%, 17.4%, 23.8%, 33.6% and 38.8% respectively. A binomial GLM model framework was used to separate the effects of year, reef and taxon on the bleaching response. Due to inconsistent sampling of sites over time, only data from the seven sites on Two Mile Reef (TMR) and the two sites on Nine Mile Reef (NMR) were included in the model. A total of 6758 coral colonies from the nine most abundantly sampled taxa were used in the assessment of bleaching response for TMR and NMR over the sample period. Taxon was shown to explain most of the variability in the bleaching response of TMR and NMR over time (40.9%). The standardized reef bleaching response of TMR and NMR indicated the same temporal trends with a range of 5% to 28% of live coral surface bleached. Standardized reef-specific BR showed periods of high (2007, 2012 and 2013) and low (2008 and 2011) bleaching response. Low BR in 2008 and 2011 did not correspond to thermal stress (≥27.5°C) suggesting that local upwelling buffered the effects of thermal stress experienced. Standardized taxon-specific bleaching response for TMR and NMR displayed large variability over time and ranged from 2.5% to 45% of live coral surface bleached, with Montipora being the most susceptible and Galaxea and Playgyra being the least. Mean site-specific BR averaged over all years, including all sites, found that Coscinaraea, Montipora, Astreopora and Anomastrea were the most susceptible taxa. This study and other recent studies draw attention to a trend of either episodic or an increasing frequency and intensity of bleaching in southern African reefs.
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Dunn, Simon Robert. "Cell death mechanisms during bleaching of the sea anemone Aiptasia sp." Thesis, University of Newcastle Upon Tyne, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.250114.
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Robison, Jennifer D. "The photophysiology of symbiotic dinoflagellates (Symbiodinium) under varying light and thermal conditions and the implications for coral bleaching." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file 8.14 Mb., 97 p, 2006. http://proquest.umi.com/pqdlink?did=1163244091&Fmt=7&clientId=8331&RQT=309&VName=PQD.
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Yeung, Yiphung. "Baseline, demography and bioerosion of Hong Kong coral communities." HKBU Institutional Repository, 2019. https://repository.hkbu.edu.hk/etd_oa/683.
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Hong Kong provides a marginal marine environment for coral growth due to its high latitude in addition to massive freshwater run-off from the Pearl River Delta. Previous studies have reported that Hong Kong waters nurture 84 species of scleractinian corals in 28 families distributed in various locations, especially the protected bays in the eastern waters. However, very little is known about the benthic composition and health of coral communities. This study aimed to 1) determine the benthic composition of local coral communities and understand the environmental determinants of coral coverage and coral community composition; 2) record coral colony size frequency distribution across these 33 sites to understand the patterns of coral recruitment in recent years; 3) quantify coral bioerosion and corallivory by the long-spined sea urchin and explore the feasibility of remediating the coral damage by a coral-associated portunid crab. Surveys were conducted at 33 sites in Hong Kong, which cover sites with the highest coral coverages that are mainly located in the north-eastern, east and south-eastern waters. A belt-transect photo quadrant method was applied. 22 hard coral genera were identified, among which the genera Porites, Platygyra and Pavona were found to be the most abundant. Most of the study sites were dominated by few genera of massive corals which led to a low diversity. Coral coverage was negatively associated with nutrient levels including nitrogen, phosphorus and organic matter deposition rates based on sediment trap data. Apart from sedimentary parameters, coral coverage was also found to be strongly negatively correlated with the density of the long-spined sea urchin Diadema setosum. Study sites were categorized into four different conservation classes with sites of higher diversity assigned a higher conservation value. These data could serve as a baseline for measuring changes in benthic composition in the future, and as a reference for management planning such as designating new marine parks. Determining the size structure can help predict how a population may change in the future and whether conservation efforts are effective in promoting the increase in numbers of individuals. To determine coral size structure in local waters, a video transect method was adopted to capture videos on the benthic substrates of the 33 study sites. In the laboratory, the video clips were analyzed to extract information on the size and growth form of all coral colonies along the transects. Size-frequency distribution plots generally showed a highly positive skewness, which indicated a dominance of small-sized (i.e. 10 - 30 cm) colonies, yet low in recruitment-sized (i.e. 5 cm) colonies. An examination of the size distribution of the most common genera showed that the distribution patterns were more genus-dependent rather than site-dependent. Also, massive corals were the most dominant growth form, while branching corals were the least common which was different from healthy tropical reefs. Apart from establishing a baseline of coral communities, coral bioerosion was further studied. Previous studies found that coral coverage and urchin density were negatively correlated in local waters. Further, severe coral bioerosion had been reported to cause community-level coral damage in several locations. Therefore, impact coral bioerosion by the sea urchin Diadema setosum and whether such impact could be remediated were further investigated in a series of controlled experiments in the field. Although sea urchins were reported to prevent shifting from coral-dominant to algae-dominate phase elsewhere, they were found to cause severe tissue loss and bioerosion at high densities in my study. Thalamita prymna, a common portunid crab in local coral communities, was found to effectively reduce coral damages including bioerosion and surface mortality. Crab predation, an overlooked relationship in coral reefs, can thus be exploited to control urchin corallivory and bioerosion. Prohibiting fish trapping in reef areas could reduce the by-catch of these crabs and protect reefs against urchin attack.
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Xie, Yang James. "Coral growth and erosion in Hong Kong /Xie Yang James." HKBU Institutional Repository, 2017. https://repository.hkbu.edu.hk/etd_oa/379.
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Coral ecosystems are highly diverse and productive ecosystems in tropical and subtropical oceans, playing a significant role in marine ecosystems. They have many important functions: a carbon sink in the global carbon cycle via calcification, habitats for many economically important species, acting as shoreline buffers, and a potential source of natural chemical substances of medical importance (Moberg et al. 1999). Growth and erosion are the two driving forces that determine the fate of a coral reef. Coral growth is achieved by calcification - the deposition of calcium carbonate skeleton by living coral polyps, and erosion refers to the removal of calcium carbonate by physical or biological factors. When calcification exceeds erosion, a reef is considered to be growing and vice versa. Hence, the study of this growth-erosion balance is the key to evaluating the health status of a reef. Hong Kong, as a marginal environment for coral survival has a remarkable diversity of coral communities in its waters. However, little is known about the calcium carbonate budget of these communities. My study thus aims to fill in this gap of knowledge in order to better understand and conserve these valuable communities. This study is timely given that many global and regional stressors are expected to affect coral calcium budget. The results of my study can contribute to a better understanding of how corals respond to environmental changes. This study aims to 1) explore any correlation between environmental factors and abundance of internal borers on corals; 2) study the growth rate of corals across different environmental gradients in Hong Kong; and 3) study the rate of erosion of corals across different environmental gradients across nine sites in Hong Kong. Field surveys were carried out at 33 sites from October 2012 to December 2012 covering two environmental gradients - from estuarine to oceanic and from sheltered to exposed. Two 50-meter transects were laid at each site and coral coverage and abundance of eroders per colony was determined using photo quadrants. Three sediment traps were also deployed at each site and collected after a month to determine sedimentation and nutrition deposition rate. Correlation analyses were conducted to explore any underlying relationships between borehole densities on corals and environmental factors. It was found that polychaete boreholes were significantly positively related to the amount of sedimentation. Also, the bioerosion of corals in Hong Kong was found out to be much more serious than that in other regions. From the 33 sites surveyed to determine borehole densities, 10 sites chosen to cover two environmental gradients were selected for more detailed studies of coral growth. Three colonies of Porties lutea of around 20 cm x 20 cm x 20 cm were collected from each site, and were cut into 1cm slabs parallel to the direction of maximum growth. X-ray radiography was done for each slab to analyze the growth rate. The growth of Porties lutea across the 10 sites were compared against other regions and underlying relationships with environmental factors were explored. It was found that the growth of corals was negatively correlated with sedimentation rate, and the calcification rates of corals in Hong Kong were much lower than those reported from many study conducted in tropical regions. To understand the rate of bioerosion of corals in Hong Kong, a study was conducted by deploying experimental coral skeleton blocks at nine chosen sites. Three blocks were deployed at each site. Blocks were retrieved after one year and scanned with MicroCT to examine the contribution on internal bioerosion by different taxa as well as the total amount of bioerosion at each site. The data were analyzed to understand internal how bioerosion is determined by environmental factors. It was found that bioerosion contributed by polychaetes had positive correlation with the sedimentation rate, which was consistent with the results found in the forth-mentioned study of coral slabs. The internal bioerosion rates of corals in Hong Kong were within the range of the corresponding data reported from overseas.
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Toyoshima, Junko. "Cell migration of zooxanthellae in the coral Montipora capitata." Thesis, University of Hawaii at Manoa, 2003. http://hdl.handle.net/10125/7050.
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Zamani, Neviaty Putri. "Effects of environmental stress on cell division and other cellular parameters of zooxanthellae in the tropical symbiotic anemone Heteractis malu, Haddon and Shackleton." Thesis, University of Newcastle Upon Tyne, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.294899.
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Hendee, James C. "A Data-Driven Soft Real-Time Expert System for Producing Coral Bleaching Alerts." NSUWorks, 2000. http://nsuworks.nova.edu/gscis_etd/579.
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In the Florida Keys there are many physical, chemical and biological events of interest and concern to personnel of the Florida Keys National Marine Sanctuary, marine biologists, oceanographers, fishermen and divers. Large volumes of continuously generated meteorological and oceanographic data from instruments in the SEAKEYS (Sustained Ecological Research Related to Management of the Florida Keys Seascape) network help to understand these events. However, since no one has the time to look at every printout of data from every station, every day, seven days a week, it is highly desirable to have an automated system that can monitor parameters of interest and produce specialized alerts of specific events, as indicated by prescribed or abnormal ranges, or combinations of parameters. A soft real-time expert system was developed to produce such alerts based on data input from the SEAKEYS network. The prototype system collected data from the Sombrero Reef station in the network and produced automated e-mail and World-Wide Web alerts when conditions were thought to be conducive to, or predictive of, coral bleaching, which occurs under environmental conditions stressful to corals. Configuration of the system included a point system for three coral bleaching models (high sea temperature only, high sea temperature plus low winds, high sea temperature plus low winds plus low tide). The approach is an important development in the use of knowledge-based systems to solve environmental problems, as it provides for knowledge synthesis (in the form of data summaries) from any environmental ASCII data stream or table, be it real-time or not.
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Suharsono. "Ecological and physiological implications of coral bleaching at Pari Island, Thousand Islands, Indonesia." Thesis, University of Newcastle upon Tyne, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308835.
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Lewis, Cynthia Fairbank. "Florida's Pillar Coral (Dendrogyra cylindrus): The Roles of the Holobiont Partners in Bleaching, Recovery, and Disease Processes." FIU Digital Commons, 2018. https://digitalcommons.fiu.edu/etd/3952.
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The iconic pillar coral, Dendrogyra cylindrus, is one of five Caribbean species listed in 2014 under the US Federal Endangered Species Act because of its extreme low abundance and continued decline in US waters. Until recently, little was known about the demographics or genetic diversity of Florida’s D. cylindrus population. This study represents the first time two holobiont partners (coral animal and associated photosynthetic algal endosymbionts) have been closely examined, spatially and temporally, in this little-studied species. The aim was to explore the influences of coral animal genotypes, mutualistic photosynthetic algal strains, and hyperthermal stress on bleaching and disease processes, resistance, and recovery through two consecutive hyperthermal events on the Florida Reef Tract (FRT) in 2014 and 2015.
Through geographically stratified, triannual assessments and tissue sampling of D. cylindrus colonies across three regions of the FRT from April 2014 to April 2016, I compared genotypic identities of the coral animal to bleaching and disease status and recovery. Additionally, I characterized the algal endosymbionts (Symbiodiniaceae family) in D. cylindrus between regions of the FRT using Illumina amplicon sequencing of the partial chloroplast 23S rDNA Domain V gene and correlated them to differential responses during bleaching and recovery. Finally, I examined the effects of hyperthermal stress on disease prevalence and changes in disease susceptibility in D. cylindrus throughout two consecutive hyperthermal events in 2014 and 2015.
Genotypic differences in D. cylindrus were associated with full or partial bleaching and/or disease resistance associated with some genets. Additionally, this study characterized unexpected diversity in the Symbiodiniaceae community within D. cylindrus and a site-specific, species-level switch in endosymbionts associated with acquired bleaching resistance during the 2015 hyperthermal event. Finally, this study demonstrated that two consecutive hyperthermal events were associated with an increase in prevalence of white plague in D. cylindrus and contributed to its susceptibility to black band disease, documented for the first time on the FRT.
Through understanding the response of the D. cylindrus holobiont partners to biotic and abiotic stressors, such as hyperthermal bleaching and associated diseases, we gained valuable insights into how this threatened species may respond to a changing climate.
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Venn, Alexander Ashley. "Coral bleaching : the significance of the molecular diversity and photoprotective pigments of zooxanthellae (Symbiodinium)." Thesis, University of York, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.423605.
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Morris, Tamaryn. "Physical oceonography of Sodwana Bay and its effect on larval transport and coral bleaching." Thesis, Cape Peninsula University of Technology, 2009. http://hdl.handle.net/20.500.11838/2038.
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Thesis (MTech (Oceanography))--Cape Peninsula University of Technology, 2009A collaborative study between Marine and Coastal Management (MCM) and the Oceanographic Research Institute (ORI) was initiated in March 2001 to investigate the physical oceanography of Sodwana Bay, South Africa, and the affects on coral communities resident to the area. A bottom-mounted Acoustic Doppler Current Profiler (ADCP) and three Underwater Temperature Recorders (UTR) were deployed to complement the long-term monitoring UTR deployed on Nine-Mile Reef (NMR) in 1994. The study was terminated after 30 months, whereby all instruments were removed except for the long-term monitoring UTR.
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Keck, Jennifer R. "Changes in Coral Populations on the Northwest Coast of Roatan, Honduras, Subsequent to the 1998 Coral Bleaching Event and Hurricane Mitch." NSUWorks, 2004. http://nsuworks.nova.edu/occ_stuetd/280.
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Long term monitoring of coral reefs on the northwest coast of Roatán, Honduras, has documented significant changes in coral cover over a seven-year period. Twenty photographic quadrats were permanently installed at approximately 12 m depth at each of three study sites located on the northwest coast of Roatán. Photographs were taken at six or twelve month intervals from 1996 through 2003. This observation period included a massive bleaching event which began in late-September of 1998, and Hurricane Mitch which struck in October of the same year. A measurement of projected surface area (PSA, cm2) was used to estimate total coral coverage. Changes in colony number, percent cover, species diversity and recruitment of all scleractinian corals were monitored within the quadrats. During the seven-year period, living coral cover decreased significantly from 30-34% to 17-20%. This represents net losses ranging between 32% and 50%. The greatest loss occurred in the year following the bleaching event and Hurricane Mitch and was largely due to the decline of the dominant reef building species Montastrea annularis, M. faveolata, and M. franksi. These three species accounted for 56% of total hard coral cover in 1996 and only 32% at the conclusion of the observation period. A sharp reduction in the total number of living colonies in the quadrats was observed with 217 of the 532 original colonies (41%) suffering complete mortality. While 117 coral recruits were identified during this period, recruitment mortality was high (40%) with only two cases of the massive frame building Montastrea species recruiting into the photostations. A combination of at least three factors have contributed to changes in the benthic community observed during this investigation: (1) the massive coral bleaching event in the fall of 1998 which disproportionately affected Montastrea spp.; (2) a category 5 hurricane; and (3) increased anthropogenic stress in the form of sedimentation and nutrient enrichment as the result of new and unregulated development.
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Hawkridge, Jane M. "Physiological and biochemical defences against environmental stressors in Cnidarians." Thesis, University of Newcastle Upon Tyne, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.262924.
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Rubio-Portillo, Esther. "Impact of environmental changes on Oculina patagonica coral holobiont." Doctoral thesis, Universidad de Alicante, 2015. http://hdl.handle.net/10045/46895.
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Andras, Tiffany D. "Seaweed allelopathy against coral: surface distribution of seaweed secondary metabolites by imaging mass sepctrometry." Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/44797.
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Coral reefs are in global decline, with seaweeds increasing as corals decrease. Though seaweeds have been shown to inhibit coral growth, recruitment, and survivorship, the mechanism of these interactions is poorly known. Here we use field experiments to show that contact with four common seaweeds induces bleaching on natural colonies of Porites rus. Controls in contact with inert, plastic mimics of seaweeds did not bleach, suggesting treatment effects resulted from allelopathy rather than shading, abrasion, or physical contact. Bioassay-guided fractionation of the hydrophobic extract from the red alga Phacelocarpus neurymenioides revealed a previously characterized antibacterial metabolite, Neurymenolide A, as the main allelopathic agent. For allelopathy of lipid soluble metabolites to be effective, the metabolites would need to be deployed on algal surfaces where they could transfer to corals on contact. We used desorption electrospray ionization mass spectrometry (DESI-MS) to visualize and quantify Neurymenolide A on the surface of P. neurymenioides and found the metabolite on all surfaces analyzed. The highest concentrations of Neurymenolide A were on basal portions of blades where the plant is most likely to contact other benthic competitors.
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Buglass, Salome. "A study on the recovery of Tobago's coral reefs following the 2010 mass bleaching event." Thesis, University of British Columbia, 2014. http://hdl.handle.net/2429/51752.
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The rise of ocean temperatures globally has become a grave threat to coral reefs, as it is increasing the severity and frequency of mass coral bleaching events and post-bleaching coral mortality. The continued existence of productive coral reefs will rely on corals’ ability to undergo recovery. In 2010, Tobago’s coral reefs were exposed to severe heat stress leading to mass bleaching of up to 29-60% of colonies at observed sites. This study evaluated the impact of coral bleaching and recovery of coral communities across three major reef systems in Tobago that differ in their exposure to terrestrial runoff. Assessments were done on the 1) density and composition of coral juveniles to characterise the levels of recruitment, 2) sedimentation rates and composition to understand its potential impact on recovery, and 3) species’ size frequency distributions in 2010, 2011 and 2013 to examine temporal changes among population size structure.
In 2013, low juvenile densities were observed (5.41 ± 6.31 m-²) at most reef sites, which were dominated by brooding genera while broadcasting genera were rare. Sediment material, measured in May and June (end of Tobago’s dry season) was mostly terrigenous and deposited at rates below coral stress threshold levels at most sites. Out of 27 species populations assessed between all sites, 4 populations mean colony size had significantly changed by the bleaching event, and only changed 5 populations over the two following years. The few populations that were significantly altered (mainly S. siderea and M. faveolata) after the bleaching saw a rise in small sized colonies, mostl likely as a result of colony fragmentation.
This study highlights that recovery via sexually produced recruits among broadcasting species was limited. While sedimentation rates were low, it is likely they are significantly higher throughout the rainy season, thus a long-term sedimentation study is highly recommended. Most coral populations resisted significant alteration from heat stress in 2010. However, given that future thermal stress is projected to become more intense, this study shows that mass bleaching disturbance could lead to decline coral population’s mean colony size, which could affect coral recovery as smaller colonies are less fecund.Arts, Faculty of
Geography, Department of
Graduate
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Fujimura, Atsushi. "Effects of Water Flow on Bleaching of Palythoa Caribaeorum." NSUWorks, 2010. http://nsuworks.nova.edu/occ_stuetd/220.
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Water flow is an important abiotic factor for corals and other cnidarians. This study shows how water flow influences bleaching in Palythoa caribaeorum. Colonies were exposed to flow (low = 3 cm s-1, high = 15 cm s-1) in two temperature regimes (low: 26.5°C, which is within natural variability on the reef where specimens were collected; high: 33.5°C, which is 3.5°C above usual summer temperature) in a unidirectional flume for 48 hours. Two sizes (small = 2.3 ± 0.2 cm, large = 7.3 ± 0.4 cm in diameter) were tested in six repeats per flow regime. Bleaching was determined by zooxanthellae count using a hemocytometer and by chlorophyll a concentration using fluorometry. Results suggest that onset of bleaching is rapid (within 48 hours) in high temperature. The low temperature did not cause significant bleaching. In the high temperature treatment, P. caribaeorum consistently bleached less in high flow. Upstream sides of large colonies bleached less than the downstream sides in high flow. In high flow, small colonies bleached less than large colonies. This suggests that enhanced diffusion of toxic oxygen species is important to mitigate bleaching and is more easily accomplished in small colonies, which may thus have an advantage during bleaching events, as has been observed in the literature.
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Brandt, Marilyn Elizabeth. "Coral Disease Epizootiology in the Florida Keys (U.S.A.) and Cayman Islands (British West Indies), and the Development of the Simulation of Infected Corals Model." Scholarly Repository, 2007. http://scholarlyrepository.miami.edu/oa_dissertations/57.
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Understanding coral disease dynamics within the heterogeneous populations in which they act is critical for predicting how the structure of reefs may change as a result of enzootic or epizootic levels of these important sources of mortality. This work focused on combining field studies and the development and testing of a spatially-explicit, individual-based epizootiological computer model with the aim of gaining a greater understanding of the dynamics and impact of white plague, a significant source of mortality on reef-building corals in the Caribbean region. Field studies focused on the incidence and distribution of all sources of coral mortality, including suspect white plague in situ, at two locations; the Florida Keys (United States of America) and Little Cayman Island (Cayman Islands, British West Indies). Results indicated that in both regions disease was the most significant source of mortality during the monitoring time periods, and that suspect white plague type II in Cayman is likely contributing to major structural changes. In Florida, observations made during a mass bleaching event indicated that a significant relationship exists between bleaching severity and disease incidence, and that mortality during the event was largely the result of disease and not bleaching. The simulation model was developed using a long-term data set from Little Cayman, and results of calibration indicated that suspect white plague type II on these reefs is transmissible between colonies within a limited field and require a yearly input from an outside source, and that host susceptibility to infection is low and likely not variable among species. Parameters describing the distribution and composition of the coral population were varied, and results indicated a significant effect of colony density, aggregation, and mean size on the impact of disease. Scenario testing of various disease management strategies indicated that should local prevention measures be developed in the future, it is they, and not treatment, that will likely be the most effective in limiting the impact of disease.
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Cowburn, Benjamin. "Coral reefs and climate change in the Indian ocean : a case study of Watamu Marine National Park, Kenya and other Indian Ocean locations." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:22c16252-bdf9-4724-a2f8-dbd4c6fe7f09.
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Coral reefs are arguably the most threatened marine habitat because of multiple anthropogenic stressors degrading the health and resilience of these systems. In the past 20 years there have been increasing observations of mass coral bleaching and mortality associated with increasing water temperatures in the tropics. Reefs provide ecosystem services worth billions of dollars to people living in tropical coastal areas and are the architects of one of the most beautiful structures found on earth. Conserving these habitats is paramount, and conservation planning must contend with climate change along with local and regional stressors. In this thesis Watamu Marine National Park in Kenya is used as a case study of the current challenges facing the conservation of reefs in a warming world. The Western Indian Ocean suffered dramatic bleaching during 1998, which caused the mortality of 70% of Watamu's corals. Using datasets from the 1980s to present the historical trajectory of Watamu's reef community is presented. The current ecosystem resilience is assessed to suggest how this reef will respond to future climate stress. It appears that Watamu's coral community has remained in an altered state post-1998, which, based on its past thermal stress and current coral community, should be resistant to future bleaching. Watamu's resilience and reef health is compared with other locations in the Indian Ocean, including reefs in Kenya and the Maldives that bleached in 1998 and examples from Mozambique and Sumatra of reefs with little evidence of historical thermal stress. Resilience is a multi-faceted process with different major components and numerous interacting factors, which act synergistically on the reef community. Conservation options and opportunities are discussed for the 6 locations examined, using current resilience models and theory as a framework for identifying priority actions. Local and regional-scale human impacts on shallow marine habitats during the last 50 years has been dramatic, and with global-scale climate change as an additional major threat, the next 50 years will be critical for the future of reefs. The locations visited during this study showed encouraging signs of resilience to past thermal stress, with evidence to suggest that corals are acclimatising and/or adapting to increasing water temperatures. The future of reefs in locations like Watamu is uncertain. Better understanding of reef ecology, appropriate conservation techniques and ultimately greater public concern for reefs is required to ensure that there is a future for these ecosystems in the Indian Ocean.
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Ambarsari, Ireng. "The nature and significance of pigments in the symbiotic algae of corals." Thesis, University of Newcastle Upon Tyne, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391321.
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Wettle, Magnus. "Monitoring coral reef bleaching from space : a feasibility study using a physics-based remote sensing approach." Thesis, University of Hull, 2005. http://hydra.hull.ac.uk/resources/hull:14048.
Full textAbstract:
There is a requirement for effective, worldwide monitoring of the health of coral reef systems, in particular the coral bleaching phenomenon. The transient nature of bleaching events, the extent and remoteness of tropical reefs, and the complex nature of the light field in submerged coral reef environments, requires novel and sophisticated remote sensing-based detection and monitoring approaches. An objective, physics-based approach (SAMBUCA) was developed for retrieving water column concentrations, bathymetry, and bottom substrate composition from remote sensing data on a per-pixel basis. MERIS images, offering a suitable spatial and temporal coverage for monitoring coral bleaching, were acquired before and during a minor bleaching event at Heron reef (Australia) in 2004. Benthic field surveys, conducted during and after the bleaching event, were analysed, and the optical properties of Heron reef substrates and waters were investigated. The latter represents the most comprehensive optical characterisation of tropical coral waters. SAMBUCA was parameterised with the optical properties of Heron coral reef waters and benthos, and applied to the FR MERIS data. Bathymetry was mapped to a high degree of accuracy, optically deep water was identified, and changes in benthic substrate composition were inferred pointing towards a minor bleaching event. Changes in per-pixel percent cover of live coral were used as a proxy indicator of coral bleaching. This study showed that environmental information on coral bleaching may be objectively retrieved at the appropriate scales for climate change assessment. Further development and validation of applying the SAMBUCA physics-based approach to global remote sensing data is recommended. Ultimately, this may lead to the implementation of regional or global tropical coral health monitoring systems. The approach presented in this thesis is unique in its application of radiative transfer theory to coral reef environments. It is furthermore applicable to other areas such as seagrass beds, and this thesis therefore represents a significant contribution to the remote sensing of (optically shallow) aquatic environments.
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Yahya, Saleh A. S. "Habitat structure, degradation and management effects on coral reef fish communities." Doctoral thesis, Stockholms universitet, Zoologiska institutionen, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-62187.
Full textAbstract:
Coral reefs are among the most diverse and productive ecosystems on earth, and are critical to the survival of tropical marine ecosystems and sustenance of local human populations. However, coral reefs are quite vulnerable to disturbances, both natural and anthropogenic. This thesis looks at how coral reef communities have responded to climactic disturbances, particularly the 1997-98 El Niño Southern Oscillation (ENSO) and subsequent coral bleaching and mortality that affected much of the Indian Ocean, including the coastal waters of Tanzania, where the study was conducted. In particular, it investigates the effects of coral bleaching, habitat degradation and reef spatial arrangement on reef fish assemblages. Habitat structural complexity and spatial arrangement of reefs had an effect on reef fish communities. Fish communities showed patterns in distribution among habitats and between patch and continuous reefs. Fishes preferred live to bleached/dead or eroded coral, but trophic groups reacted differently to patch and continuous reefs. There were slight changes in fish abundance and significant changes in fish diversity on experimental, bleached branching Acropora coral plots over a period of one year. While fish abundance on one site increased shortly after a bleaching event, 6 years later fish abundance had decreased significantly. Conversely, coral reef communities in northern Tanzania had changed little over an 8-year period, with minor changes associated with the 1997-98 ENSO and the presence or absence of fisheries management. The coral reefs in the region were found to show high variability in community structure and responses of associated fish and invertebrate communities. The findings of this thesis indicate the importance of habitat structure and spatial arrangement of reefs, the detrimental effects of coral bleaching, and the possibility that some reefs and some (generalist) reef fish taxa may exhibit resilience to climate change.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.
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Barnes, Brian Burnel. "The Combined Effects of Light and Temperature on Coral Bleaching: A Case Study of the Florida Reef Tract Using Satellite Data." Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4863.
Full textAbstract:
Coral reefs are greatly impacted by the physical characteristics of the water surrounding them. Incidence and severity of mass coral bleaching and mortality events are increasing worldwide due primarily to increased water temperature, but also in response to other stressors. This decline in reef health demands clearer understanding of the compounding effects of multiple stressors, as well as widespread assessment of coral reef health in near-real time.
Satellites offer a means by which some of the physical stressors on coral reefs can be measured. The synoptic spatial coverage and high repeat sampling frequency of such instruments allow for a quantity of data unattainable by in situ measurements. Unfortunately, errors in cloudmasking algorithms contaminate satellite derived sea surface temperature (SST) measurements, especially during anomalously cold events. Similarly, benthic interference of satellite-derived reflectance signals has resulted in large errors in derivations of water quality or clarity in coral reef environments.
This work provides solutions to these issues for the coral reef environments of the Florida Keys. Specifically, improved SST cloudmasking algorithms were developed for both Advanced Very High Resolution Radiometer (AVHRR; Appendix A) and Moderate Resolution Imaging Spectroradiometer (MODIS) data (Appendix B). Both of these improved algorithms were used to reveal the extent and severity of a January 2010 cold event that resulted in widespread mortality of Florida Keys corals. Applied to SST data from 2010, the improved MODIS cloudmasking algorithm also showed improved quantity of SST retrievals with minimal sacrifice in data quality.
Two separate algorithms to derive water clarity from MODIS measurements of optically shallow waters were developed and validated, one focusing on the diffuse downwelling attenuation coefficient (Kd, m-1) in visible bands (Appendix C), the other on Kd in the ultraviolet (Appendix D). The former utilized a semi-analytical approach to remove bottom influence, modified from an existing algorithm. The latter relied on empirical relationships between an extensive in situ training dataset and variations in MODIS-derived spectral shape, determined using a stepwise principal components regression. Both of these algorithms showed satisfactory validation statistics, and were used to elucidate spatiotemporal patterns of water clarity in the Florida Keys. Finally, an approach was developed to use Landsat data to detect concurrent MODIS-derived reflectance anomalies with over 90% accuracy (Appendix E). Application of this approach to historical Landsat data allowed for long-term, synoptic assessment of the water environment of the Florida Keys ecosystem. Using this approach, shifts in seagrass density, turbidity increases, black water events, and phytoplankton blooms were detected using Landsat data and corroborated with known environmental events.
Many of these satellite data products were combined with in situ reports of coral bleaching to determine the specific environmental parameters individually and synergistically contributing to coral bleaching. As such, SST and visible light penetration were found to be parsimoniously explaining variance in bleaching intensity, as were the interactions between SST, wind and UV penetration. These relationships were subsequently used to create a predictive model for coral bleaching via canonical analysis of principal coordinates. Leave-one-out-cross-validation indicated that this model predicted `severe bleaching' and `no bleaching' conditions with 64% and 60% classification success, respectively, nearly 3 times greater than that predicted by chance. This model also showed improvement over similar models created using only temperature data, further indicating that satellite assessment of coral bleaching based only on SST data can be improved with other environmental data. Future work should further supplement the environmental parameters considered in this research with databases of other coral stressors, as well as improved quantification of the temperature at the depth of corals, in order to gain a more complete understanding of coral bleaching in response to environmental stress.
Overall, this dissertation presents five new algorithms to the field of satellite oceanography research. Although validated primarily in the Florida Keys region, most of these algorithms should be directly applicable for use in other coastal environments. Identification of the specific environmental factors contributing to coral bleaching enhances understanding of the interplay between multiple causes of reef decline, while the predictive model for coral bleaching may provide researchers and managers with widespread, near real-time assessments of coral reef health.
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Tenorio, Arthur de Albuquerque. "Mudanças entre autotrofia e heterotrofia em corais construtores de recifes Mussismilia hispida: abordagem utilizando ácidos graxos marcadores tróficos." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/21/21134/tde-21022017-152905/.
Full textAbstract:
Os recifes de coral estão entre os ambientes marinhos mais produtivos e ricos em biodiversidade. Esta biodiversidade está em parte associada a complexas estruturas formadas por corais escleractíneos. Apesar da importância ecológica, social e econômica dos recifes de corais, eles são expostos a várias ameaças relacionadas às atividades humanas. Dentre os impactos antrópicos em recifes, o branqueamento, ou perda de zooxantelas, é o mais notável e é diretamente relacionado à mortalidade dos corais. Por possuírem uma associação simbiótica com essas zooxantelas, alguns corais escleractíneos são considerados mixotróficos, caracterizados por modos de alimentação autotrófico (através de simbiose com o dinoflagelado Symbiodinium) e heterotrófico (predação sobre zooplâncton). Alguns estudos comprovam que corais com maior capacidade de alimentação heterotrófica são mais resistentes ao branqueamento e, consequentemente, às alterações climáticas. A fim de analisar se o coral escleractíneo Mussismilia hispida, é capaz de alternar seu modo nutricional entre predominante autotrófico e predominante heterotróficos, dezoito colônias foram amostradas ao longo de um ano. Marcadores Tróficos de Ácidos Graxos (FATM, na sigla em inglês) foram utilizados para determinar a fonte nutricional de carbono em tecido de corais. A concentração de células de Symbiodinium e a temperatura local também foram avaliadas. Branqueamento foi observado nos meses mais quentes do ano, quando a concentração de Symbiodinium diminuiu, voltando a aumentar nos meses mais frios. O marcador para dieta heterotrófica CGA (C20: 1ω9) foi encontrado em amostras de zooplâncton de toda a área de estudo. Em laboratório, colônias sem acesso a zooplâncton apresentaram perda significativa deste marcador após 10 dias. Amostras de colônias naturalmente branqueadas não apresentaram nenhum vestígio dos marcadores de autotrofia SDA (18: 4ω3) e DPA (22: 5ω3), mas continham tanto CGA e DHA (22: 6ω3). Isso confirmou que SDA e DPA são marcadores autotróficos viáveis e CGA é um marcador de heterotrofia. FATM relacionados com autotrofia apresentaram padrão semelhante ao observado para as concentrações de Symbiodinium e foram positivamente correlacionados com a densidade numérica de simbiontes e negativamente com a temperatura. Para explorar os dados de concentração dos FATM, o Índice Trófico de Corais foi desenvolvido para exibir as alternâncias entre modos nutricionais. Mussismilia hispida de fato alterna entre predominância de modo nutritivo ao longo do ano, sendo mais heterotrófica em períodos mais quentes e em condições climáticas adversas, porem na maior parte do ano é predominantemente autotrófica. A validação dos ácidos graxos marcadores tróficos específicos como referência para autotrofia e heterotrofia em corais abre perspectivas para novos estudos em ecologia trófica bêntica em recifes de coral. Este trabalho também inclui o primeiro monitoramento de um ano do comportamento alimentar em um coral hermatípico no Atlântico Sul e o acompanhamento de um evento de branqueamento.Coral reefs are among the most productive and biodiverse marine environments. This remarkable biodiversity is partly associated to the complex structures formed by scleractinian corals. Despite the ecological, social and economic importance of coral reefs, they are constantly exposed to several threats mainly related to human activities. Climate changes are one of the most notable impacts of human activity related to coral mortality, mainly due to coral bleaching. Some scleractinian corals are proved to be mixotrophs, displaying both autotrophic (through Symbiodinium) and heterotrophic (predation on zooplankton) nutrition modes. Many studies emphasize that corals with greater capability of heterotrophic feeding are more resilient to bleaching and consequently to climate change. In order to analyze whether the endemic scleractinian coral Mussismilia hispida is capable of shifting from predominant autotrophic and predominant heterotrophic in Ubatuba-SP, 18 colonies were sampled monthly for 12 months. The Fatty Acid Trophic Markers (FATM) approach was used to determine the source of carbon on coral tissues. Symbiodinium cell density and local seawater temperature were also assessed. A mild bleaching was observed showing a decrease in Symbiodinium numerical density during warmer months, but increasing in colder months. Reference samples validated the relation between all selected FATM and its corresponding nutritional mode. The heterotrophic feeding marker CGA (C20:1ω9) was found in zooplankton samples collected throughout the study area. Laboratory starved colonies (no access to zooplankton) lost any trace of this marker after 10. Samples from naturally bleached colonies presented no traces of the autotrophic feeding markers SDA (18:4ω3) and DPA (22:5ω3), but contained both CGA (C20:1ω9) and DHA (22:6ω3). These results confirmed that the FATM analyzed where reliable trophic markers. Autotrophic FATM presented a pattern similar to that observed for Symbiodinium concentration in M. hispida tissues and were positively correlated with the symbiont and negatively with temperature. The Coral Trophic Index showed that M. hispida undergoes shifts in nutritional modes along the year, being more heterotrophic in adverse conditions. The validation of specific FATM as proxies for autotrophic and heterotrophic feeding in corals opens new perspectives for further studies in benthic trophic ecology in coral reefs. This work also presents the first yearlong monitoring of the feeding behavior in a hermatypic coral in the South Atlantic and the monitoring of a mild bleaching event.
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Kabay, Lystina. "Population Demographics and Sexual Reproduction Potential of the Pillar Coral, Dendrogyra cylindrus, on the Florida Reef Tract." NSUWorks, 2016. http://nsuworks.nova.edu/occ_stuetd/433.
Full textAbstract:
The pillar coral, Dendrogyra cylindrus, has been commonly described as widely distributed, but rare throughout its geographical range in the Caribbean. Having recently been listed as Threatened under the US Endangered Species Act, an understanding of population status is needed to promote species conservation and population recovery. Previous to this study the status of the pillar coral population in the state waters of Florida, U.S.A, was relatively unknown primarily due to few colonies being recorded and no comprehensive summary of population abundance, distribution or health being completed. Along with various environmental and anthropogenic factors affecting the pillar coral population on the Florida Reef Tract (FRT), it appears that reproductive limitations may also be contributing to species decline and limiting population recovery as evidenced by the lack of reported juvenile D. cylindrus colonies reported on the Florida Reef Tract (FRT) in the past 17 years.
The factors contributing to this phenomenon are currently unknown, however are suspected to be derived from the pillar corals reproductive biology. Being described as a gonochoric, broadcast spawner, sexual reproduction relies on the synchronous release of gametes from colonies of separate sexes, and with low adult colony densities reported for the pillar coral on the FRT, gamete concentrations from both sexes may be too low for fertilization to occur.
In 2014 submissions of pillar coral locations from the scientific and lay community were compiled and 610 D. cylindrus colonies along Florida Reef Tract were identified (Lunz et al. 2016). In my study, I describe the population structure of D. cylindrus for the southeast Florida region of the FRT which includes 65 of the total 610 colonies. For each of the 65 colonies, colony depth, demographic, and condition data were recorded including size (length, width, and height), percent of recent mortality, and presence and severity of disease and bleaching. Out of all locations identified in this region, about 50% contained only a single colony of D. cylindrus and the maximum number of colonies per site was 14. Throughout the duration of the study, devastating losses of live tissue were observed following the bleaching and disease events impacting the Florida Reef Tract in 2014, 2015, and 2016 and the status of the southeast Florida population of pillar coral is at serious risk of local extinction.
To investigate the ability of colonies of D. cylindrus to sexually reproduce (referred to as sexual reproduction potential) tissue samples were collected from 95 colonies within 15 sites along the FRT and were prepared for histological analysis. The sex of each colony, sizes of gametes in mature developmental stages, the abundance of gametes per cm2 of tissue, and sex ratios for locations on the FRT were reported. All tissue samples from male and female colonies contained gametes that were ≥90% mature; however sex ratios were found to be skewed in all locations, deviating significantly from the 1:1 ratio expected for typical resource allocation in random mating. Hermaphroditic colonies of D. cylindrus are described for the first time throughout its geographical range in this study and comparisons to gonochoristic colonies confirmed that these hermaphrodites are sexually reproductive individuals.
Results from this effort provide a more thorough understanding of the reproductive biology of D. cylindrus and essential data for the support of future conservation management and restoration strategies for this FRT population and comparative data for other Caribbean populations.
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Charpentier, Bernadette. "The Role of Colony Size in the Resistance and Tolerance of Scleractinian Corals to Bleaching Caused by Thermal Stress." Thèse, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/30662.
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In 2005 and 2010, high sea surface temperatures caused widespread coral bleaching on Jamaica’s north coast reefs. Three shallow (9m) reef sites were surveyed during each event to quantify the prevalence and intensity of coral bleaching. In October 2005, 29-57% of the colonies surveyed were bleached. By April 2006, 10% of the corals remained pale/partially bleached. Similarly, in October 2010, 23-51% of corals surveyed at the same sites were bleached. By April 2011, 12% of the colonies remained pale/partially bleached. Follow-up surveys revealed low coral mortality following both events, with an overall mean of 4% partial colony mortality across all species and sites observed in April 2006, and 2% in April 2011. Mixed effects models were used to quantify the relationship between colony size and (a) bleaching intensity, and (b) bleaching related mortality among coral species. The bleaching intensity model explained 51% of the variance in the bleaching response observed during the two events. Of this 51%, fixed effects accounted for ~26% of the variance, 17% of which was attributed to species-specific susceptibility to bleaching , 5% to colony size, <1% colony morphology and 4% to the difference in bleaching intensity between the two events. The random factor (site) accounted for the remaining ~25% of the variance. The mortality model explained 16% of the variance in post bleaching mortality with fixed effects, including colony size, morphology and species explaining ~11% of the variance, and the random effect (site) explaining 5%. On average, there was a twofold difference in bleaching intensity between the smallest and the largest size classes. Modelling the relationship between colony level characteristics and site-specific environmental factors on coral species’ susceptibility to thermal stress can shed light on community level responses to future disturbances.
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DE, FALCO CHIARA. "Sea Surface Temperature patterns and ocean dynamics in the Maldivian region." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2021. http://hdl.handle.net/10281/313702.
Full textAbstract:
La frequenza degli episodi di coral bleaching è aumentata interrottamente nelle ultime decadi a causa dell’incremento di temperatura registrato nei diversi oceani del pianeta. Nell’Arcipelago Maldiviano, tali eventi sono stati osservati principalmente nei mesi seguenti il picco di episodi El-Niño molto intensi. Il bleaching tuttavia non è stato uniforme e alcuni reef sono stati colpiti solo marginalmente. Ho utilizzato i dati da satellite e un modello oceanico regionale (CROCO) per investigare la variabilità, sia spaziale sia temporale, della temperatura superficiale dell’oceano (SST) e quantificare l’entità relativa di episodi legati ad ENSO, confrontandoli con l’effetto dell’incremento della temperatura negli ultimi decenni. In linea con altri studi effettuati, è stato confermato che il trend di temperatura aumenta significativamente la frequenza di episodi di stress termico per i coralli. È stato anche scoperto che, durante la stagione più calda, l’interazione tra le correnti e la ripida batimetria è responsabile di una diminuzione locale della temperatura elimina virgole avanati e dietro nell’Arcipelago di circa 0.2°C rispetto all'oceano circostante. Questo raffreddamento riduce notevolmente la frequenza di condizioni di mortalità per i coralli. La riduzione della SST attorno alle Maldive è probabilmente collegata all’Island Mass Effect: l’incremento di produttività intorno a isole di dimensione ridotte scoperto negli anni sessanta e documentato in tutto il mondo. Nonostante il suo effetto sulla produttività marina, l’esatto quadro dei processi che stanno dietro al raffreddamento locale e l’input di nutrienti che accresce la produttività è ancora incerto. Dall'analisi delle variazioni di SST e della produttività primaria netta (NPP) intorno a numerose isole ed arcipelaghi di piccole dimensioni sono stati identificati due tipi di pattern. Intorno ad isole con un'altitudine considerevole e dimensioni maggiori, infatti, sono visibili anomalie calde/fredde, probabilmente corrispondenti ad aree di upwelling e downwelling. Aree più calde non sono invece visibili intorno ad isole di dimensioni minori. Sono diversi i processi, sia oceanici sia atmosferici, che potrebbero essere coinvolti e contribuire a generare il pattern di temperatura. Ho studiato nel dettaglio il caso delle Maldive, utilizzando CROCO - aumentando la risoluzione - ed un modello di particles tracking, Ariane, ed è emerso che il meccanismo predominante varia durante l’anno e dipende dalla direzione e magnitudo delle correnti. Vicino alle Maldive il rallentamento delle correnti a causa dell’attrito dovuto ad una batimetria poco profonda produce un forte shear verticale, che favorisce il mescolamento verticale e produce un raffreddamento quasi simmetrico intorno alle isole. Un altro meccanismo domina il pattern di raffreddamento quando le correnti sono particolarmente intense, come durante i monsoni: forti correnti zonali attraversano l’Arcipelago e generano wake intense con un elevato shear orizzontale; un intenso upwelling si origina nelle scie, creando un segnale di temperature asimmetrico (raffreddamento maggiore nella scia delle isole) e offuscando gli effetti del rafforzato mescolamento verticale.The frequency of coral bleaching events has been increasing in recent decades due to the temperature rise registered in most regions near the ocean. Their occurrence in the Maldivian Archipelago has been observed in the months following the peak of strong El Niño events. Bleaching has not been uniform, and some reefs have been only marginally impacted. I have used satellite observations and a regional ocean model (CROCO) to explore the spatial and temporal variability of sea surface temperatures (SSTs), and quantify the relative magnitude of ENSO-related episodes with respect to the recent warming. In line with other studies, it is confirmed that the long-term trend in SST significantly increases the frequency of stress conditions for the Maldivian corals. It is also found that the interaction between currents and the steep bathymetry is responsible for a local cooling of about 0.2°C in the Archipelago during the warmest season, with respect to the surrounding waters. This cooling largely reduces the frequency of mortality conditions. The reduced SST surrounding the Maldives is probably linked to the Island Mass Effect: the enhanced productivity around small islands discovered in the sixties and documented worldwide. Despite its effects on marine productivity, the exact description of the physical processes behind the local cooling and nutrient input that enhances productivity is still unclear. From the analysis of SST variations and net primary productivity (NPP) around small islands and archipelagos, two kinds of signals can be identified, depending on the altitude and dimension of the islands. Around islands with considerable elevation and greatest diameters, cold/warm anomalies, most likely corresponding to upwelling/downwelling zones, emerge. Warmer areas don’t appear around smaller islands that usually display only a local cooling. Several oceanic and atmospheric processes might be involved. The case of the Maldives has been analyzed in detail using CROCO with increased resolution and a particle tracking model: Ariane. More than one process might coexist in generating the described patterns, the prevailing one varying along the year and depending on the strength and direction of the incoming flow. Near the Maldives, the frictional break of the currents in the presence of shallow bathymetry produces a strong vertical shear in the flow that favors vertical mixing and produces a nearly symmetric cooling around the islands. A different mechanism dominates the cooling pattern when the currents are particularly intense, such as during the monsoons: intense zonal currents cross the Archipelago and give rise to intense wakes with large horizontal shear; strong upwelling originates in the lees, creating an asymmetric temperature signal (larger cooling in the lee of the islands) and obfuscating the effects of the enhanced vertical mixing.
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Putchim, Lalita [Verfasser], Claudio [Akademischer Betreuer] [Gutachter] Richter, and Barbara E. [Gutachter] Brown. "Coral bleaching and recovery in the Thai Andaman Sea / Lalita Putchim ; Gutachter: Richter Claudio, E. Barbara Brown ; Betreuer: Richter Claudio." Bremen : Staats- und Universitätsbibliothek Bremen, 2017. http://d-nb.info/1141861992/34.
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Barnes, Brian Burnel. "The Combined Effects of Light and Temperature on Coral Bleaching| A Case Study of the Florida Reef Tract Using Satellite Data." Thesis, University of South Florida, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3604824.
Full textAbstract:
Coral reefs are greatly impacted by the physical characteristics of the water surrounding them. Incidence and severity of mass coral bleaching and mortality events are increasing worldwide due primarily to increased water temperature, but also in response to other stressors. This decline in reef health demands clearer understanding of the compounding effects of multiple stressors, as well as widespread assessment of coral reef health in near-real time.
Satellites offer a means by which some of the physical stressors on coral reefs can be measured. The synoptic spatial coverage and high repeat sampling frequency of such instruments allow for a quantity of data unattainable by in situ measurements. Unfortunately, errors in cloudmasking algorithms contaminate satellite derived sea surface temperature (SST) measurements, especially during anomalously cold events. Similarly, benthic interference of satellite-derived reflectance signals has resulted in large errors in derivations of water quality or clarity in coral reef environments.
This work provides solutions to these issues for the coral reef environments of the Florida Keys. Specifically, improved SST cloudmasking algorithms were developed for both Advanced Very High Resolution Radiometer (AVHRR; Appendix A) and Moderate Resolution Imaging Spectroradiometer (MODIS) data (Appendix B). Both of these improved algorithms were used to reveal the extent and severity of a January 2010 cold event that resulted in widespread mortality of Florida Keys corals. Applied to SST data from 2010, the improved MODIS cloudmasking algorithm also showed improved quantity of SST retrievals with minimal sacrifice in data quality.
Two separate algorithms to derive water clarity from MODIS measurements of optically shallow waters were developed and validated, one focusing on the diffuse downwelling attenuation coefficient (Kd, m-1 ) in visible bands (Appendix C), the other on Kd in the ultraviolet (Appendix D). The former utilized a semi-analytical approach to remove bottom influence, modified from an existing algorithm. The latter relied on empirical relationships between an extensive in situ training dataset and variations in MODIS-derived spectral shape, determined using a stepwise principal components regression. Both of these algorithms showed satisfactory validation statistics, and were used to elucidate spatiotemporal patterns of water clarity in the Florida Keys. Finally, an approach was developed to use Landsat data to detect concurrent MODIS-derived reflectance anomalies with over 90% accuracy (Appendix E). Application of this approach to historical Landsat data allowed for long-term, synoptic assessment of the water environment of the Florida Keys ecosystem. Using this approach, shifts in seagrass density, turbidity increases, black water events, and phytoplankton blooms were detected using Landsat data and corroborated with known environmental events.
Many of these satellite data products were combined with in situ reports of coral bleaching to determine the specific environmental parameters individually and synergistically contributing to coral bleaching. As such, SST and visible light penetration were found to be parsimoniously explaining variance in bleaching intensity, as were the interactions between SST, wind and UV penetration. These relationships were subsequently used to create a predictive model for coral bleaching via canonical analysis of principal coordinates. Leave-one-out-cross-validation indicated that this model predicted `severe bleaching' and `no bleaching' conditions with 64% and 60% classification success, respectively, nearly 3 times greater than that predicted by chance. This model also showed improvement over similar models created using only temperature data, further indicating that satellite assessment of coral bleaching based only on SST data can be improved with other environmental data. Future work should further supplement the environmental parameters considered in this research with databases of other coral stressors, as well as improved quantification of the temperature at the depth of corals, in order to gain a more complete understanding of coral bleaching in response to environmental stress.
Overall, this dissertation presents five new algorithms to the field of satellite oceanography research. Although validated primarily in the Florida Keys region, most of these algorithms should be directly applicable for use in other coastal environments. Identification of the specific environmental factors contributing to coral bleaching enhances understanding of the interplay between multiple causes of reef decline, while the predictive model for coral bleaching may provide researchers and managers with widespread, near real-time assessments of coral reef health.
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Otis, Daniel Brooks. "Spatial and Temporal Variability of Remotely Sensed Ocean Color Parameters in Coral Reef Regions." Scholar Commons, 2012. http://scholarcommons.usf.edu/etd/4379.
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The variability of water-column absorption due to colored dissolved organic matter (CDOM) and phytoplankton in coral reef regions is the focus of this study. Hydrographic and CDOM absorption measurements made on the Bahamas Banks and in Exuma Sound during the spring of 1999 and 2000 showed that values of salinity and CDOM absorption at 440nm were higher on the banks (37.18 psu, 0.06 m^-1), compared to Exuma Sound (37.04 psu, 0.03 m^-1). Spatial patterns of CDOM absorption in Exuma Sound revealed that plumes of CDOM-rich water flow into Exuma Sound from the surrounding banks. To examine absorption variability in reef regions throughout the world, a thirteen-year time series of satellite-derived estimates of water-column absorption due to CDOM and phytoplankton were created from Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and Moderate Resolution Imaging Spectroradiometer (MODIS) data. Time series data extracted adjacent to coral reef regions showed that variability in absorption depends on oceanographic conditions such as circulation patterns and winds as well as proximity to sources of light-absorbing materials that enter the water column, such as from terrestrial runoff. Waters near reef regions are generally clear, exhibiting a lower "baseline" level of CDOM absorption of approximately 0.01 m^-1 at 443nm. The main differences between regions lie in the periods during the year when increased levels of absorption are observed, which can be triggered by inputs of terrestrially-derived material, as in the Great Barrier Reef lagoon, or wind-driven upwelling as in the Andaman Sea and eastern Pacific Ocean near Panama. The lowest CDOM absorption levels found were approximately 0.003 m^-1 at 443nm near the islands of Palau and Yap, which are removed from sources of colored materials. The highest absorption levels near reefs were associated with wind-driven upwelling during the northeast monsoon on the Andaman coast of Thailand where values of CDOM absorption at 443nm reached 0.7 m^-1. Simulations of the underwater light field based on satellite-derived absorption values revealed that changes in absorption have a strong influence on light levels to which corals are exposed, particularly in the ultraviolet region of the spectrum, where CDOM is the primary absorber of light. Episodes of coral bleaching during 1998 and 2002 were found to be associated with elevated seawater temperatures as well as decreased levels of CDOM absorption, indicating that corals were exposed to light stress along with thermal stress during periods of bleaching.
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Drenkard, Elizabeth Joan. "Exploring the climate change refugia potential of equatorial Pacific coral reefs." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/97339.
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Thesis: Ph. D., Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2015.Cataloged from PDF version of thesis.
Includes bibliographical references.
Global climate models project a 21st century strengthening of the Pacific Equatorial Undercurrent (EUC). The consequent increase in topographic upwelling of cool waters onto equatorial coral reef islands would mitigate warming locally and modulate the intensity of coral bleaching. However, EUC water is potentially more acidic and richer in dissolved inorganic nutrients (DIN), both widely considered detrimental to coral reef health. My analysis of the Simple Ocean Data Assimilation product indicates that the EUC has indeed strengthened over the past 130 years. This result provides an historical baseline and dynamical reference for future intensification. Additionally, I reared corals in laboratory experiments, co-manipulating food, light and CO2 (acidity) to test the role of nutrition in coral response to elevate CO2 conditions. Heterotrophy yields larger corals but CO2 sensitivity is independent of feeding. Conversely, factors that enhance zooxanthellate photosynthesis (light and DIN) reduce CO2 sensitivity. Corals under higher light also store more lipid but these reserves are not utilized to maintain calcification under elevated CO2 My results suggest that while mitigation of CO2 effects on calcification is not linked to energetic reserve, EUC fueled increases in DIN and productivity could reduce effects of elevated CO2 on coral calcification.
by Elizabeth Joan Drenkard.
Ph. D.
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Scucchia, Federica. "Transcriptional profiles inferring thermal stress responses of the coral Oculina patagonica from the Eastern Mediterranean Sea." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/17967/.
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During the past several decades, corals worldwide have been dealing with a considerable increase in water temperature due to climate change, which is predicted to increase the frequency of coral bleaching and mass mortality events. Nevertheless, corals show differences in stress susceptibility and they are not all affected evenly. The symbiotic coral Oculina patagonica from the Eastern Mediterranean Sea can thrive in relatively unstable environments and is considered a stress-tolerant species. In this study, baseline expression and temporal dynamics of induction of a 70-kDa heat shock protein (HSP70) after an acute heat stress were analyzed in O. patagonica to investigate the influence of its peculiar physiological traits on stress responsiveness. Furthermore, data collected were further discussed within a comparative analysis with similar findings reported in 5 temperate corals of the Mediterranean Sea (Franzellitti et al., 2018). Results show that O. patagonica hsp70 transcriptional response aligns with the formerly observed high resistance for elevated sea water temperatures of this species. The multispecies comparison shows that hsp70 expression varies in accordance with the stress sensitivity of coral populations inhabiting different thermal environments and possessing different trophic strategies and morphologies. This study also reports an analysis of the post heat-stress transcriptional regulation of transcripts related to energy metabolism (gadph), redox regulation (sod), and DNA damage (bcl-2 and bax), disclosing the time line of the events occurring in O. patagonica in response to an acute heat stress, which aligns with its quick recovery from bleaching. These molecular processes analysis is particularly demanding for corals inhabiting the Mediterranean Sea, in light of projected scenarios of anthropogenic global change.
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Bellantuono, Anthony John. "Acclimatization of the Tropical Reef Coral Acropora millepora to Hyperthermal Stress." FIU Digital Commons, 2013. http://digitalcommons.fiu.edu/etd/1005.
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The demise of reef-building corals potentially lies on the horizon, given ongoing climate change amid other anthropogenic environmental stressors. If corals cannot acclimatize or adapt to changing conditions, dramatic declines in the extent and health of the living reefs are expected within the next half century. The primary and proximal global threat to corals is climate change. Reef-building corals are dependent upon a nutritional symbiosis with photosynthetic dinoflagellates belonging to the group Symbiodinium. The symbiosis between the cnidarian host and algal partner is a stress-sensitive relationship; temperatures just 1°C above normal thermal maxima can result in the breakdown of the symbiosis, resulting in coral bleaching (the loss of Symbiodinium and/or associated photopigments) and ultimately, colony death. As ocean temperatures continue to rise, corals will either acclimatize or adapt to changing conditions, or will perish. By experimentally preconditioning the coral Acropora millepora via sublethal heat treatment, the coral acquired thermal tolerance, resisting bleaching during subsequent hyperthermal stress. The complex nature of the coral holobiont translates to multiple possible explanations for acclimatization: acquired thermal tolerance could potentially originate from the host itself, the Symbiodinium, or from the bacterial community associated with the coral. By examining the type of in hospite Symbiodinium and the bacterial community prior acclimation and after thermal challenge, it is shown that short-term acclimatization is not due to a distinct change in the dinoflagellate or prokaryote community. Though the microbial partnerships remain without considerable flux in preconditioned corals, the host transcriptome is dynamic. One dominant pattern was the apparent tuning of gene expression observed between preconditioned and non-preconditioned treatments, showing a modulated transcriptomic response to stress. Additionally several genes were upregulated in association with thermal tolerance, including antiapoptotic genes, lectins, and oxidative stress response genes. Upstream of two of these thermal tolerance genes, inhibitor of NFκB and mannose-binding lectin, DNA polymorphisms were identified which vary significantly between the northern and southern Great Barrier Reef. The impact of these mutations in putative promoter regions remains to be seen, but variation across thermally-disparate geography serves to generate hypotheses regarding the role of regulatory element evolution in a coral adaptation context.
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Bonalume, Clauber. "Utilizaçao de tecnicas fotometricas para estudo do branqueamento e da quantidade de algas simbiontes em colonias coralinas." [s.n.], 2006. http://repositorio.unicamp.br/jspui/handle/REPOSIP/250453.
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Orientador: Ines JoekesDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química
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Resumo: Corais marinhos do mundo inteiro estão ameaçados pelas alterações climáticas que vêm acontecendo nas duas últimas décadas. O aquecimento da superfície terrestre associado à intensificação do fenômeno El Niño têm causado prejuízos à saúde dos corais marinhos com intensidade, extensão e escala temporal sem precedentes. Quando expostos a situações de estresse ambiental, corais podem sofrer branqueamento, perdendo suas algas simbiontes, as zooxantelas, e morrer se não as recuperarem. Desta forma, métodos de avaliação da saúde dos corais tornam-se necessários. Dois métodos fotométricos foram desenvolvidos neste trabalho. No primeiro, utilizou-se a técnica de reflectância difusa para estudo do histórico de branqueamento de fatias de núcleos de esqueletos coralinos através da análise da cor do núcleo na direção do crescimento do coral. Esse método mostrou-se sensível à variação de cor ao longo da amostra e foi capaz de evidenciar o histórico conhecido de branqueamento de 2 entre 3 amostras analisadas. O método é promissor para o estudo de esqueletos, mas depende sensivelmente do tratamento prévio das amostras. No segundo, fotografaram-se amostras de Mussismilia híspida em seu ambiente natural na Laje de Santos. Foram colhidas amostras dos corais fotografados e foi determinada a densidade de zooxantelas em cada amostra. Utilizando o software MatLab e uma rotina específica de análise multivariada, estabeleceu-se uma correlação entre aspectos da imagem digital e a densidade de zooxantelas. A correlação obtida é boa, com erros menores que 35 % na estimativa da densidade de zooxantelas a partir das imagens digitais. O método é bastante promissor e tem a vantagem de ser não destrutivo.
Abstract: In the last two decades marine corals around the world have been threatened by weather global changes. Coral health is declining at unprecedented intensity, extension and temporal scale, by world surface heating associated with the strengthening of the El Niño Southern Oscillation. When exposed to environmental stresses coral can bleach, loosing their symbiotic algae, the zooxanthellae, and die if they are permanently lost. The development of methods capable to assess coral health is necessary. Two photometric methods were developed. In the first one, difuse reflectance spectrophotomety was used to analize the bleaching history of slices of coral skeletons by color analysis along the growing direction of the colony. The method showed apropriate sensibility for measuring color changes along the samples and was able to disclose the bleaching history in two of the three samples studied. However, results depend strongly on the previous treatment of the skeleton samples. In the second method, samples of Mussismilia híspida coral colonies were photographed in their natural habitat in the Laje de Santos marine conservation park. Small samples of the photographed coral were taken and the density of zooxanthellae in each sample was measured. Using the MatLab sofware and a specific algorithm for multivariated image analisys (MIA), a correlation between features of the images and the density of zooxanthellae was established. The correlation obtained is fairly good, with less than 35 % error in the estimation of zooxanthellae density from the digital images. The method is quite promissing and has the advantage of being nondestructive.
Mestrado
Físico-Química
Mestre em Química
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Pratte, Zoe A. "Investigating the Driving Mechanisms Behind Differences in Bleaching and Disease Susceptibility Between Two Scleractinian Corals, Pseudodiploria Strigosa and Diploria Labyrinthiformis." FIU Digital Commons, 2015. http://digitalcommons.fiu.edu/etd/2217.
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Disease and bleaching are two conditions which commonly lead to coral death. Among coral species, susceptibility to disease and bleaching is variable, and Pseudodiploria strigosa tends to be diseased more than Diploria labyrinthiformis, while D. labyrinthiformis bleaches more readily. The focus of this dissertation was to investigate and compare multiple components of these two coral species, and identify how they may relate to disease and bleaching resistance. Compenetnts examined included the surface mucopolysacharide layer (SML) thickness, gene expression, microbial associates, and a white plague aquarium study. The SML thickness decresased with increasing temperature regardless of coral species, indicating that SML thickness does not likely play a role in differences between susceptablities of these two coral species. However, Diploria labyrinthiformis had a lower mortality rate at 31°C, had fewer differentially expressed genes assossiated with stress, and upregulated genes associated with innate immunity in the summer, all of which may contribute to its relative disease resistance. The bacterial associates of each coral species were also monitored. Differences between the two coral species were primarily caused by Clostridia, Gammaproteobacteria, and rare species which may contribute to the relatively higher disease susceptibility of P. strigosa. Lastly, an aquarium study suggested that a potential pathogen of the Roseobacter clade infects both D. labyrinthiformis and P. strigosa, and might be transmitted by the Cryptochiridae gall crab, indicating that potential disease vectors associated with these two coral species may also play a role in disease resistance and resilience.
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Grasso, Peter T. "Coral Genotype Influence on Growth and Stress Resistance in Acropora cervicornis: Investigating Potential Energy Tradeoffs." NSUWorks, 2016. http://nsuworks.nova.edu/occ_stuetd/404.
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Over the last few decades coral reefs have faced unprecedented declines in health due to natural and anthropogenic sources. Until recently few studies have examined genotypic variation of growth and thermal stress resistance in Acropora cervicornis. This study aims to assess the potential for energy trade-offs between growth and thermal stress resistance by following 120 coral fragments from 12 genotypes of Acropora cervicornis over the course of 15 months to determine average growth rates for each genotype. Following the completion of the growth observation a bleaching event occurred in the lower Florida Keys providing the opportunity for examining thermal stress resistance. We found that the coral genotype had a significant effect on growth and survival; however no significant correlation was observed between growth under normal conditions and thermal stress resistance. This result shows that there is not a trade-off between growth and thermal stress resistance and that a genotype’s ability to resist thermal stress cannot be predicted from growth under normal conditions. The lack of a trade-off facilitates intraspecific competition. For genotypes with similar thermal stress tolerances but different growth characteristics, the increase in frequency of disturbances could result in the increased abundance of faster growing genotypes relative to the slow growing genotypes. These results emphasize the importance of maintaining coral nurseries as gene banks to protect the genetic diversity of the reef area in which it is located. Through protecting a wide variety of genotypes, the likelihood of preserving those that have a high thermal tolerance, disease resistance, or faster growth rates is increased.
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Rosing, Trina. "Using Structure-from-Motion Technology to Compare Coral Coverage on Restored vs. Unrestored Reefs." Wittenberg University Honors Theses / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=wuhonors1623948204369104.
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Paul, Nicole Christine. "Variable Recovery of the Massive Coral, Porites Lobata, in Response to El Nino-Southern Oscillation Events at Devil's Crown, Galapagos, Ecuador." NSUWorks, 2012. http://nsuworks.nova.edu/occ_stuetd/93.
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Porites lobata is an important reef building coral in the tropical eastern Pacific and the dominant Porites species in the Galápagos archipelago. Following the 1982-83 El Niño-Southern Oscillation the Galápagos Islands experienced 97-99% coral mortality, leaving many areas throughout the archipelago denuded of corals. Because very few long term assessments have been conducted on the growth and resilience of P. lobata to natural disturbances in the Galápagos Islands (Glynn et al., 2001; Glynn et al., 2009), benthic surveys were performed on a uniquely dense aggregation of P. lobata colonies at Devil’s Crown, Floreana Island between 1993 and 2011. Annual changes in live tissue area were calculated for the majority of the population (n=17) using Coral Point Count with Excel extensions (CPCe 3.6) software to determine growth and recovery trends for this aggregation. Total live tissue area (n=10) increased from 1993 to 2011, however due to high interannual variability this increase was not significant. Within this overall pattern, a general trend of decline was observed in live tissue cover from 1993 to 2000, with increases in tissue area observed from 2000 to 2011. Severe bleaching (85-100%) was observed during the 1998 survey, followed by 42% tissue loss (n=10), coinciding with sea water warming associated with the very strong 1997-1998 El Niño-Southern Oscillation event. Subsequent regrowth of coral tissue was observed during the 2001 survey with continued recovery through 2009. Multiple comparison testing revealed a significant difference between the impacted state (1999) and the recovered state (2009), (p = 0.002, Dunn’s method, n=17), suggesting this aggregation required a period of ten years to recover from this disturbance. During this recovery period the moderately strong 2007-2008 La Niña, with accompanying stressful low temperatures, occurred but did not interrupt tissue regrowth. Warmer than average sea surface temperatures occurred during the warm months from 2008 to 2011, during which time a cool period occurred from 2010 to 2011. While the magnitude and duration of temperature anomalies during warming were not as great as those observed during the 1997-98 ENSO, low temperatures observed during the cool period were similar to those experienced throughout the 2007-08 La Niña. During this time total live tissue cover was reduced by 19% (n=10); however it is unknown whether this was due to warming or the following cool period. Based on results from the 1997-98 El Niño and 2007-08 La Niña, this reduction in live tissue was most likely caused by elevated sea surface temperatures. Data on the growth and resilience of P. lobata populations at Devil’s Crown will be used for conservation and management of this important resource.
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Mendez-Ferrer, Natasha. "Photic Stress in Symbiont-Bearing Reef Organisms: Analyses of Photosynthetic Performance." Scholar Commons, 2016. http://scholarcommons.usf.edu/etd/6322.
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Photo-oxidative stress is one of the key factors that can induce bleaching in reef organisms. With the decline of coral reefs and recurrent bleaching events, many studies have focused on understanding the mechanism behind this phenomenon. Two of the hypotheses that explain how the photosynthetic performance of the symbiont is affected and influences bleaching are: (1) disruption of the photosynthetic pathway by direct damage to the photosystem II (PSII), and (2) by inhibition of the Calvin-Benson cycle. In this dissertation I examine different aspects of photosynthetic performance in symbiont-bearing reef organisms and how this is influenced by symbiont loss and changes in photic stress as a result of different levels of irradiance modulated by time of the year (e.g., season) and depth; and take a closer look into primary productivity by symbionts with controlled laboratory experiments.
Field experiments during 2012–2013 at Tennessee Reef, FL, assessed the photosynthetic performance of PSII in the diatom-bearing foraminifer, Amphistegina gibbosa, and the anthozoans: Palythoa cariabeorum, Siderastrea siderea, and Montastraea cavernosa. Data collected for the bleaching trends of A. gibbosa revealed that bleaching rates are higher in the summer months than in winter. Photochemical efficiencies of PSII in A. gibbosa, as measured with PAM fluorometry on the day of collection, were more variable in the shallow site (6 m) than in the deeper site (18 m). Also, photochemical efficiencies at the shallow site were lower during the summer months than during winter months. At the 18 m site, photochemical efficiencies did not exhibit a clear seasonal trend. Depth also had an effect on the measured photochemical efficiencies of the anthozoans. Photochemical efficiencies were lower and more variable in colonies at 6 m compared to colonies from 18 m. Although previous studies have reported seasonal effects on the photochemical efficiency of some coral colonies, that trend was not apparent in this study.
Photoacclimation and productivity were assessed for A. gibbosa using rapid light curves (RLC) and photosynthesis vs. irradiance curves (P-E). Maximum relative electron transport rate (rETRmax) as described by RLCs was significantly different between A. gibbosa without visual signs of bleaching and those with severe bleaching. Individuals with partial bleaching had a rETRmax that was intermediate between the other two categories. The P-E curves showed a similar trend. In this case individuals that were non- or partly bleached had significantly higher photosynthesis maxima than those with severe bleaching. The onsets of photosynthesis and saturation irradiance were not significantly different among the categories of bleaching analyzed. Results from this dissertation suggest that A. gibbosa has the capability to detect and digest damaged symbionts, that the symbionts even in the deeper chambers react in a similar way to irradiance, but that in severe cases of bleaching the symbionts may not produce enough energy to sustain the requirements of the host, even in non-stressful conditions.
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Reynolds, David A. "The effects of the red tide producing dinoflagellate, Karenia brevis, and associated brevetoxins on viability and sublethal stress responses in scleractinian coral: a potential regional stressor to coral reefs." UNF Digital Commons, 2018. https://digitalcommons.unf.edu/etd/829.
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Coral cover is in decline on a global scale, with increased mortality events being attributed to a number of global and regional stressors. While the impacts of global stressors (e.g. sea surface temperature rise, ocean acidification) are well documented, there is growing interest in identifying and understanding the impacts of regional stressors. The reason for this change in focus is that regional stressors can often work in combination, sometimes synergistically, with global stressors and that stressors on a regional scale tend to be more easily mitigated by management practices. One regional stressor that impacts a myriad of marine organisms in the southeastern United States is the annual red tide blooms produced by the dinoflagellate, Karenia brevis. Their impacts, along with the lipid soluble polyether neurotoxins they produce, termed brevetoxins, are well studied in economically important organisms, such as bivalves. However, little is known of their impacts on organisms that possess ecological importance, such as species of scleractinian coral. To address this gap in knowledge, a multifaceted study is discussed herein, which evaluated the effects of ecologically relevant concentrations of K. brevis and associated brevetoxins on different coral life history stages and coral species. The second chapter addresses the impacts of red tide on larval behavior, settlement and survival of the coral species Porites astreoides, as well as impacts of photochemical efficiency and oxidative stress within different coral species (P. astreoides larvae, P. astreoides adults, Acropora cervicornis, Cladocora arbuscula, and Phyllangia americana). The third chapter confers the use of broad-scale proteomic analysis to identify the cellular response of the non-model coral species, P. astreoides, following exposure to red tide. Coral larvae actively avoided both medium and high bloom conditions of K. brevis and brevetoxins, while percent larval settlement and survival were impacted following exposure to high bloom concentrations of K. brevis. Photochemical efficiency of in hospite Symbiodinium was reduced following exposure to both K. brevis and brevetoxin in P. astreoides larvae, as well as exposure to K. brevis in P. astreoides adults, while being unimpacted in A. cervicornis. Compared to controls, high bloom conditions resulted in an increase in biomarkers of lipid peroxidation in C. arbuscula. This was also seen in P. astreoides larvae at 24 hours; however, this difference was indistinguishable following 48 hours. Surprisingly, no other biomarker of oxidative stress analyzed were impacted. Broad-scale proteomic analysis of P. astreoides following exposure to red tide conditions revealed variable changes in proteome expression depending on if the corals were exposed to K. brevis or brevetoxins. Exposure to brevetoxins resulted in differential expression of proteins related to DNA organization, chromatin formation and transcription expression; while exposure to K. brevis resulted in differential expression of proteins related to redox homeostasis, protein folding, energy metabolism, and production of reactive oxygen species. The results of this study demonstrate the potential for annual red tide blooms to act as a regional stressor on coral species. They highlight the ability of red tide conditions to negatively impact coral at multiple life history stages and that the extent of these effects may be species specific. They also provide further incite of coral’s response to red tide exposure at the cellular level.
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Souza, Izabel Maria Matos de. "Avalia??o da cobertura e monitoramento do branqueamento de corais nos recifes de Maracaja?/RN." Universidade Federal do Rio Grande do Norte, 2012. http://repositorio.ufrn.br:8080/jspui/handle/123456789/14046.
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Previous issue date: 2012-06-18Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior
Coral bleaching has been increasingly the focus of research around the world since the early 1980s, when it was verified to be increasing in frequency, intensity and amount of areas affected. The phenomenon has been recorded since 1993, associated with elevation of the sea surface temperature due to El Ni?os and water thermal anomalies, according to most reports around the world. On the coast of Rio Grande do Norte, Brazil, a mass coral bleaching event was recorded in the Environmental Protection Area of Coral Reefs (APARC) during March and April 2010, when the water temperature reached 34?C for several days. About 80% of the corals in Maracaja? reef-complex exhibited partial or total bleaching. The aims of this study were to verify representativeness of coral coverage and how the bleaching dynamic has developed among different species. Coral coverage was estimated according to Reef Check Brazil protocol associated with quadrant method, and bleaching was evaluated from biweekly visual surveys in 80 colonies of Favia gravida, Porites astreoides, Siderastrea stellata and Millepora alcicornis. At the same time temperature, pH, salinity and horizontal transparency, as well as mortality and disease occurrence were monitored. Analysis of variance and Multiple Regression from the perspective of time lag concept were used to evaluate the bleaching dynamics among species and the relationship between variation of means of bleaching and variations of abiotic parameters, respectively. Species showed significant differences among themselves as to variation of means of bleaching over time, but the dynamic of variation exhibited similar patterns
O branqueamento de corais tem sido o foco de um n?mero crescente de estudos desde a d?cada de 1980 quando foi verificado o aumento na frequ?ncia, intensidade e n?mero de ?reas atingidas. No Brasil o fen?meno tem sido registrado desde 1993, associado ? eleva??o da temperatura das ?guas superficiais do mar decorrente de eventos de El-Ni?os e anomalias t?rmicas, conforme a maioria dos relatos em todo o mundo. No litoral do Rio Grande do Norte registrou-se branqueamento em massa de corais nos recifes da ?rea de Prote??o Ambiental dos Recifes de Corais (APARC) em Mar?o e Abril de 2010, quando a temperatura da ?gua atingiu valor de 34?C durante v?rios dias. Cerca de 80% dos corais do complexo recifal de Maracaja? exibiram branqueamento parcial ou total. Os objetivos deste trabalho foram verificar qual a representatividade do recobrimento de corais no Parracho de Maracaja? e como a din?mica de branqueamento se desenvolve entre as esp?cies. A cobertura de corais foi estimada de acordo com o protocolo Reef Check Brasil associado ao m?todo de quadrado, e o branqueamento foi avaliado a partir de censos visuais quinzenais em 80 col?nias de Favia gravida, Porites astreoides, Siderastrea stellata e Millepora alcicornis. Ao mesmo tempo foram monitorados a temperatura da ?gua, pH, salinidade e transpar?ncia horizontal, e a ocorr?ncia de mortalidade e sintomas de doen?as. Foram utilizadas a An?lise de Vari?ncia e a Regress?o M?ltipla sob a perspectiva do conceito do time lag para avaliar a din?mica de branqueamento entre as esp?cies e a rela??o da varia??o das m?dias com a varia??o dos fatores abi?ticos, respectivamente. As esp?cies apresentaram diferen?a significativa entre si quanto ? varia??o das m?dias de branqueamento ao longo do tempo, mas a din?mica de varia??o exibiu padr?es semelhantes
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Schoepf, Verena. "Physiology and Biogeochemistry of Corals Subjected to Repeat Bleaching and Combined Ocean Acidification and Warming." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1376923711.
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Meunier, Valentine. "Interactions entre coraux scléractiniaires, les diazotrophes planctoniques et le picoplancton dans le contexte du changement climatique." Electronic Thesis or Diss., Sorbonne université, 2021. http://www.theses.fr/2021SORUS332.
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Les coraux constructeurs de récifs, sont à la fois autotrophes (ils vivent en symbiose avec des microalgues de la famille des Symbiodiniaceae) et hétérotrophes, c’est à dire qu’ils sont capables de se nourrir sur une gamme de proies allant de la matière organique dissoute, au plancton. Les récifs coralliens sont menacés par le réchauffement climatique, qui perturbe la symbiose entre les coraux et leurs symbiontes, entraînant un blanchissement massif des coraux. Les diazotrophes planctoniques, capables de fixer le diazote (N2) atmosphérique en azote (N) biodisponible (l’ammonium, NH4+), et de transférer cet N Dérivé de la Diazotrophie (appelé DDN) le long du réseau trophique, pourraient constituer une source alternative de nutriments pour les coraux. Seule une étude préliminaire a montré qu’une espèce corallienne pouvait se nourrir sur ces diazotrophes planctoniques (Benavides et al., 2016). Des diazotrophes symbiotiques vivent également en association avec les coraux et leurs transfèrent aussi du DDN. Dans le contexte du changement climatique, où les coraux sont menacés à la fois par l’acidification (AO) et le réchauffement des océans, ce travail se propose d’étudier le rôle de la diazotrophie planctonique et symbiotique dans l’acquisition d’N par les coraux et dans leur résistance/résilience à ces changements. (i) Dans un premier temps, nous avons déterminé les quantités d’N apportées par l’ingestion de diazotrophes planctoniques et symbiotiques au sein de trois espèces coralliennes. Nos résultats ont révélé que l’apport d’N par l’ingestion de diazotrophes planctoniques était répandu chez les coraux et que les taux d’assimilation par cette voie étaient mille fois plus importants que ceux obtenus par les diazotrophes symbiotiques. (ii) Nous avons également montré que des coraux blanchis étaient capables d’augmenter leur consommation de plancton diazotrophe mais également d’augmenter plus spécifiquement leur ingestion de Synechococcus. (iii) Une expérience menée in situ, sur des coraux se développant dans des résurgences naturelles de CO2 en Papouasie-Nouvelle Guinée, où la pCO2 est proche de celle prévue d’ici la fin du siècle, nous a permis de démontrer que les taux d'assimilation de DDN étaient plus élevés que dans le site contrôle, avec une communauté de diazotrophes spécifique à ce site, les Alphaprotéobactéries. (iv) Enfin, nous avons quantifié en laboratoire, les effets d’un stress de température sur les principaux paramètres physiologiques de coraux non nourris, ou nourris exclusivement avec des diazotrophes planctoniques. Ces coraux bénéficiant d’un apport en DDN par le plancton diazotrophe seraient plus résistants au blanchissement. Ils conservent davantage leurs Symbiodiniaceae et maintiennent leurs taux de croissance et de transfert d’électrons. Étant donné la forte abondance de picoplancton dans les eaux des lagons oligotrophes, nos résultats suggèrent que les coraux, capables d'ajuster la communauté de leur diazotrophes symbiotiques, et d'exploiter les sources de plancton riches en N, seraient plus résistants face au réchauffement climatique et à l’AOReef building corals are both autotroph (they live in symbiosis with intracellular dinoflagellate of the Symbiodiniaceae family, which provide them with photosynthates) and heterotroph, they are able to feed on a wide range of prey from organic matter to plankton. Coral reefs are threatened by global warming, which disrupts the symbiosis between corals and their symbionts, leading to mass coral bleaching. Planktonic diazotrophs, which have the particularity of fixing the atmospheric dinitrogen (N2) and transferring this diazotroph-derived nitrogen (N) (called DDN) along the food web, could be an alternative nutrient source for corals. Only a preliminary study has shown that one coral species could feed on planktonic diazotrophs (Benavides et al., 2016). Symbiotic diazotrophs also live in association with corals and transfer them some DDN. In the context of climate change, where corals are threatened by both acidification (OA) and ocean warming, this work proposes to study the role of planktonic and symbiotic diazotrophs in N acquisition by corals and in their resistance/resilience to these changes. (i) First, we quantified DDN assimilation rates through heterotrophic nutrition of diazotrophs and symbiotic diazotrophs. Our results reveal the importance of N intake through heterotrophy on planktonic diazotrophs as N assimilation rates through this way were a thousand times higher than those obtained via endosymbiotic diazotrophs. (ii) We also showed for the first time that thermally stressed corals are able to increase not only their consumption of planktonic diazotrophs and plankton that likely benefited from N2 fixation, but also more specifically their ingestion of a very specific taxonomic group of picoplankton : the ubiquitous marine cyanobacterium Synechococcus. (iii) An experiment conducted in situ, on corals growing in natural CO2 vents in Ambitle (Papua New Guinea), where the pCO2 is close to that expected by the end of the century, allowed us to demonstrate that DDN assimilation rates in the Symbiodiniaceae were significantly higher in comparison to an ambient CO2 site, concomitant with a restructured diazotroph community and the particular prevalence of Alphaproteobacteria. (iv) Finally, in laboratory conditions, we have quantified the effects of temperature stress on corals fed exclusively with planktonic diazotrophs. Corals benefiting from DDN supplied by diazotrophic plankton, would be more resistant to bleaching, they retain more of their Symbiodiniaceae and maintain their growth and electron transfer rates (in Photosystem II, ETR) compared to unfed corals. Given the high abundance of picoplankton in oligotrophic waters at large, our results suggest that corals capable of adjusting their diazotrophic communities and exploiting N-rich picoplankton sources to offset their increased N requirements, may be able to cope better with OA and global warming
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Underwood, Linda. "Awareness and action : coral bleaching : research study on changed behavior upon receiving information concerning coral bleaching effects." Master's thesis, 2019. http://hdl.handle.net/10362/68458.
Full textAbstract:
Dissertation presented as the partial requirement for obtaining a Master's degree in Statistics and Information Management, specialization in Information Analysis and ManagementCoral reefs are living organisms that act as an important ecosystem for many different kinds of invertebrates and vertebrates. They are essential for marine life to survive yet also provide many benefits for human life as well. “Coral bleaching” is caused by climate change due to the increase in temperature in the ocean’s water which starves the organism and what remains is only its white skeleton. This is one of the biggest threats to coral reefs. This study aims to understand whether, when given information about coral bleaching specifically, people are more likely to participate in actions that prevent coral bleaching through global warming and if so, what their main motive is to do so. This is important for organizations whose goal is to protect the coral reef so that they can make more effective campaigns. A survey is conducted with questions specifically targeting these main goals and statistically analyzed before and after a passage containing facts regarding coral bleaching, to determine if there are any changes in people’s standpoint. Results showed a lack of knowledge of the importance of coral reefs for human life which increases likelihood to take action against coral bleaching once reading the passage, when considering all respondents. Previous belief in cause and existence of climate change influences the likelihood to take action overall. However, Gender and Age play a role in increased awareness and likelihood to take action against coral bleaching.
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Liao, Chiu-Yeh, and 廖萩燁. "Effects of temperature on stony coral bleaching." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/36285925567978835071.
Full textAbstract:
碩士國立中山大學
海洋科學系研究所
102
Events of high temperature causing large scale coral bleaching have been reported worldwide in last several decades. However, the role of low temperature, temperature fluctuation and other environmental factors in relation to coral bleaching is still insufficient. Here, the effects of temperature (high, low and fluctuation), typhoons and climate indices on stony coral bleaching were investigated seasonally at INF and EFF of Kenting, Taiwan, during May 2005 - May 2013. Based on the records of 3 fixed transect lines in each site, the branch Acropora (40.7 ± 33.5%) is the most abundant stony coral at INF. In contrast, the clump Porites (17.5 ± 14.4%) and the branch Millepora (12.5 ± 21.6%) are the major species at EFF. In a total of 32 surveys, coral bleaching occurred every season at both INF and EFF and bleaching times were 16~22 and 5~21, respectively. Further analyses with representative transect lines of INF5 and EFF showed that the Degree Heating Weeks (DHWs) at INF and EFF were 29.5 and 28.5°C. In the first season, coral bleaching was positively correlated with large temperature fluctuation 28 days before the bleaching survey at INF, but not at EFF. In the second season, no correlation between coral bleaching and heat or temperature fluctuation was observed at both sites. In the third season, coral bleaching was significantly correlated with continuous hot at both sites. In the fourth season, coral bleaching was correlated with 28 days’ heat before the survey at INF. And large temperature fluctuation 7 days before survey also affected the bleaching. In contrast, coral bleaching was correlated with small temperature fluctuation 14 days before survey at EFF. Typhoons didn’t have significant effect on coral bleaching at both sites and Pacific Decadal Oscillation index (PDO index) was positively correlated with coral bleaching at INF with one month time lag. In summary, stony coral bleaching occurred in every season at both sites. Heat, great or small temperature fluctuation all affected on the bleaching events. Difference in species composition of stony coral community is probably a crucial factor resulting in dissimilar bleaching patterns at INF and EFF.
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Morris, Luke Aaron. "The role of nutrients in coral bleaching." Thesis, 2021. https://researchonline.jcu.edu.au/75350/1/JCU_75350_Morris_2021_Thesis.pdf.
Full textAbstract:
Luke Morris investigated the role of nutrients in coral bleaching. While he found that environmental nutrients do not substantially influence heat tolerance, nutritional destabilisation of the coral-algal symbiosis was integral to explaining coral bleaching and mortality. These results inform the management and understanding of mass coral bleaching and mortality events.