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1
Bollati, Elena. "Fluorescence on coral reefs." Thesis, University of Southampton, 2018. https://eprints.soton.ac.uk/424758/.
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Coral reefs are highly biodiverse ecosystems and provide vital resources for the human population. Due to increasing pressure by climate change and local stressors, these ecosystems currently face a global crisis. The development of tools to monitor how coral reefs respond to environmental change is a key aspect of the conservation of their biodiversity and resources. A number of reef organisms produce fluorescent molecules, including photosynthetic pigments and green fluorescent protein (GFP)-like pigments found in Anthozoa. These pigments are responsive to environmental conditions and can be optically monitored in vivo, making them a promising tool to investigate organism- and community-level processes on coral reefs. In this thesis, the fundamental principles and technological developments necessary for the application of fluorescence as a biomarker are explored. First, the mechanisms regulating coral fluorescence are considered for two functionally and biochemically distinct groups of GFP-like proteins. In mesophotic and depth-generalist symbiotic corals, incomplete light-driven maturation of the red GFP-like protein pool is shown to determine the spectrum of fluorescence emission. A role of this mechanism in adaptation to the reduced mesophotic light spectrum is discussed. In corals from shallow water environments, enhancement of internal light fluxes due to reduced absorption by symbiont pigments during bleaching is shown to induce expression of GFPlike proteins. High-level expression of these pigments in bleached tissue is shown to promote recovery of the symbiotic algae complement after a stress event. Second, a novel approach to fluorescence imaging for coral reef surveys is presented. The method enables automatic classification of reef benthic organisms based on the intensity of fluorescent signal in different excitation and emission bands. These findings demonstrate the potential of fluorescence as an in vivo marker for physiological and ecological studies of coral reef organisms, contributing to ongoing efforts to monitor and preserve the health of these ecosystems.
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Matthews, Elizabeth. "Community-based and collaborative management of coral reefs and coastal resources in Palau /." View online ; access limited to URI, 2007. http://0-digitalcommons.uri.edu.helin.uri.edu/dissertations/AAI3284827.
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Lokrantz, Jerker. "Exploring the resilience in coral reefs /." Stockholm : Department of systems ecology, Stockholm university, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-26659.
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Mason, Benjamin M. "The importance of detritus and microenvironment nutrient enrichment to the growth of coral reef macroalgae, Halimeda and Dictyota /." Electronic version (PDF), 2004. http://dl.uncw.edu/etd/2004/masonb/benjaminmason.html.
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Haas, Andreas. "Coral reefs in a time of change." Diss., lmu, 2010. http://nbn-resolving.de/urn:nbn:de:bvb:19-116066.
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Paredes, Gustavo Adolfo. "Degradation and recovery of Caribbean coral reefs." Diss., [La Jolla, Calif.] : University of California, San Diego, 2009. http://wwwlib.umi.com/cr/ucsd/fullcit?p3356249.
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Thesis (Ph. D.)--University of California, San Diego, 2009.Title from first page of PDF file (viewed July 7, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.
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Harris, Daniel. "Physical processes and morphodynamics of coral reefs." Thesis, The University of Sydney, 2013. http://hdl.handle.net/2123/10435.
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Coral reefs are valuable ecosystems due to their ability to support many diverse biological and geological assemblages. They are also of social and economic significance with the Great Barrier Reef (GBR) an important national symbol for Australia and a UNESCO world heritage site. Ecological studies have observed a decline in coral reef health in many parts of the world over the last few decades, due to human pressures (both local and global) in addition to natural variations of the environmental setting. However, the spatial and temporal resolution of most ecological assessments is inevitably limited, particularly on the scales of decadal to millennial coral reef change. Geological studies on the other hand accurately assess coral reef evolution over thousands of years but struggle with small scale changes in geomorphology and biological assemblages. Studies with a geomorphic and morphodynamic focus are required in order to bridge the gap between the ecological and geological understanding of coral reef evolution and provide information regarding the decadal to millennial change in reef geomorphology and carbonate production. In spite of this, physical process studies on coral reefs are few, particularly when compared to siliciclastic settings (such as estuaries and beaches) with a limited understanding of the mechanisms initiating geomorphic change in coral reef systems. The physical processes (waves and currents) acting on a coral reef windward platform and back-reef sand apron were assessed, along with morphological surveys and sedimentologic and chronostratigaphic reconstruction of sand apron evolution. Dating of dead patch-reefs buried by sand apron accretion was conducted in order to examine long-term sand apron evolution. Sampling and dating of fossil micro-atolls was also conducted in order to establish potential sea level history for the southern GBR. The sand apron geomorphology was shown to have channel formations as well as shallower areas which were associated with buried patch reefs. These features affected current flow on the sand apron with channels directing current off the sand apron, mainly during ebb tides (ebb dominated), into the lagoon or towards the reef crest and the shallow areas which were dominated by lagoonward directed flow across the sand apron (flood dominated). This is similar to the processes in siliciclastic environments, such as estuaries, and indicates that morphodynamic relationships between current flow and geomorphology occur in coral reef environments. In spite of this, average current flow did not exceed the required velocity to entrain sediment; sediment entrainment was only caused by short term peaks in current due to waves. These results showed that sediment entrainment under modal low-energy conditions does occur in back-reef environments; albeit on a small scale (only 3.5% of all recorded waves could entrain sediment). Most entrainment occurred at higher tidal stages (when depth over the reef platform (hd > 1 m) when potential mobility PM of sediment could be up to 40%. Spatial variation in PM and significant wave height (Hs) were found to extend beyond cross-reef attenuation of wave height and energy. The attenuation of Hs across the sand apron could be reasonably described based on the changes in offshore wave height, depth over the reef platform, and cross-reef distance from the reef rim (Xd). However, these variables could not explain along-reef trends within the data. To assess the along-reef variation in wave characteristics an additional distance value was introduced (Xpd) which combined the cross-reef distance to the reef rim (Xd) and the along-reef distance from the initial point of wave refraction on the reef rim (Xp). Spatial changes in wave height, PM wave velocity and grain size correlated with changes in Xpd. An empirical model was developed which could calculate wave height based on a few basic inputs of offshore wave weight, offshore wave direction, Xd and Xp. This model can be used in windward reef environments to not only assess the spatial variation in wave characteristics but also potential areas of sediment mobility and trends in sediment grain size. Radiocarbon ages and elevations of the fossil micro-atolls show that relative sea level was between 1-1.3 m higher than present between 3800-2200 cal. yr. BP. This data set is the first direct constraint through fixed biological indicators on sea level during the Holocene highstand in the southern GBR. These dates suggest that the Holocene sea level for the southern GBR follows a similar trend to current sea level curves for the east Australian coastline where the Holocene highstand was between 7000-2000 cal. yr. BP before falling to its present level. Rapid sand apron development occurred between 6000-2000 cal. yr. BP with most of the sand apron established during this period. Little or no sand apron development has occurred in the last 2000 years. This correlates with the micro-atoll data in this thesis and the sea level fall observed in previous studies at approximately 2000 cal. yr. BP. The fall in sea level caused an ecological shift on the reef platforms from live coral to algal dominated turning off the majority of carbonate production. It is likely that this led to a hiatus in sand apron development that has persisted for 2000 years. A conceptual model was developed that describes the non-linear lagoonal infill and sand apron development during the Holocene due to variations in sea level. In this model, rapid development of both reef platforms and back-reef sedimentary formations initially occurred during catch-up reef growth phase or when the windward margins reached sea level. This highly productive state may persist if sea level remains consistent and allows for productive live coral growth on reef platforms. A fall in sea level strands live coral on the reef platforms, leading to a turn-off of carbonate production and sediment input resulting in a reduction in the rate of lagoon infill. This conceptual framework has significant consequences for traditional reef growth models which generally show linear trajectories of reef evolution and also for assessments of coral reef response under future climate change predicted variations in sea level.
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Langmead, Olivia. "Coral community dynamics and disturbance : a modelling approach for Caribbean coral reefs." Thesis, University of Warwick, 2002. http://wrap.warwick.ac.uk/58615/.
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The capacity of reefs to recover after disturbance is fundamental to prediction of their stability. This is particularly relevant now, following the global decline of reefs during the last decades. A discrete, spatially explicit model (probabilistic cellular automaton) was developed to simulate a Caribbean coral community. Community complexity was generated from behaviour of fundamental units of corals, the polyps. Regarding background disturbance, area disturbed and patch size were investigated; both were equally important in driving coral community structure and diversity. A powerlaw model was developed to predict natural disturbances, and implemented in later testing of system dynamics. Corals were assigned differential susceptibilities to background disturbances. Results assessed against field data showed that most modelled species had realistic colony size frequency distributions (though 20% had insufficient comparison data). Following model development, recovery from single impacts (simulated warming events) was tested. Model responses indicate importance of local setting to community resilience. Individual susceptibility of species was mediated by life history strategy investment. Application of a warming sequence of predicted anomalies for this century was then introduced. Community composition changed betwee1 0-40 years from predominantly persistent, large, slow growing species to small, fecund, fast growing species. After 40 years a phase shift occurred in which algae dominated the community. It is concluded that the future may herald declines in the main Caribbean reef-building species, in ways that match several previous but largely untested speculations. This model indicates that there will be serious implications to reefs, including their numerous commercially important species. The model includes all known major life history attributes of the corals, based on real data. Structural properties of the model were tested for stability and computational efficiency. Disturbances of several types were investigated; natural background disturbance, and warming events, both as single and repeated incidents to assess recovery dynamics in the light of ongoing, intensifying climate-mediated global changes.
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Nicholls, Thaddeus Allen. "Decadal-Scale Changes on Coral Reefs in Quintana Roo, Mexico." DigitalCommons@USU, 2008. https://digitalcommons.usu.edu/etd/238.
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In 1988 data on coral reef community composition were collected from two areas, Akumal and Chemuyil, Quintana Roo, Mexico, ranging from 5-35m depth. These areas were revisited in 2005 and data were collected by the same methods and at the same depths as in 1988. Data from 1988 and 2005 were compared to determine if the coral reefs had undergone significant changes, and what specific changes had occurred. Chi-square analysis determined that community composition data collected in 1988 are significantly different from data collected in 2005 at all sites and depths within the categories of corals, gorgonians, sponges, and macroalgae. Mann-Whitney U analyses were performed on abundance data for coral, gorgonians, sponges, macroalgae, crustose coralline algae, erect coralline algae/calcareous algae, filamentous/multi-species turf algae, and non-living substrate. Results from the Mann-Whitney U analysis varied between sites; however significant trends of increasing macroalgae, crustose coralline algae and filamentous/multi-species turf, and declining non-living substrate were observed at almost all sites. H' biodiversity indices J' evenness values and species number (S) were calculated for all sites over the two time periods, with no discernable trends observed. Increases in crustose coralline algae and filamentous/multi-species turf algae suggest that eutrophication and overfishing may be responsible for the trends observed on the reefs at Akumal and Chemuyil. Anecdotal accounts also suggest that eutrophication from septic water flowing through the highly porous karst limestone of the Yucatan Peninsula may be the largest malefactor causing the observed changes. The increase in filamentous/multi-species turf algae exhibited by the data suggests that eutrophication is predominantly responsible for the alternate states of the reefs. Furthermore, evidences indicative of other forms of stress on the reefs, such as bleaching, scraped or broken coral heads, disease, and sedimentation, were rarely observed.
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Siciliano, Daria. "Latitudinal limits to coral reef accretion : testing the Darwin point hypothesis at Kure Atoll, Northwestern Hawaiian Islands, using new evidence from high resolution remote sensing and in situ data /." Diss., Digital Dissertations Database. Restricted to UC campuses, 2005. http://uclibs.org/PID/11984.
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Noren, Hunter KG. "Can Twilight Reefs Usher In A New Dawn For Depauperate Shallow Coral Reefs?" Thesis, NSUWorks, 2016. https://nsuworks.nova.edu/occ_stuetd/421.
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As shallow reefs continue to decline, scientists are searching for the key to their persistence; as it turns out, they may just need to look deeper. Below many shallow tropical reefs, there exist healthy and more stable mesophotic coral reef communities. The ability of these reefs to act as a refuge for declining shallow populations has garnered significant interest among the scientific community; however, the reproductive and larval aspects necessary for this to occur are unknown. This study assesses the ability of deep reefs to act as a reproductive refuge for shallow counterparts by examining gametic compatibility, viability and larval settlement preferences. Gametes from Orbicella franksi inhabiting the shallow (14-20m) and the upper mesophotic (27-32m) were introduced in a series of inter- and intra-depth crosses and found to be compatible. Larval settlement experiments found no natal depth preference, with deep larvae significantly preferring to settle on shallow conditioned substrate. Our findings support the plausibility of healthy mesophotic reefs acting as a refuge for depauperate shallow populations by (1) providing gametes to mix with limited shallow gametes resulting in increased fertilization and (2) providing larvae that recruit and repopulate shallow reefs. This is the first study to comprehensively evaluate the Deep Reef Refugia Hypothesis from a reproductive and larval settlement standpoint. Our results suggest a close coupling between shallow and mesophotic reefs through gamete and larval export and illustrate the current and future importance of these mesophotic reefs.
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Fonseca, Carolyn E. "The value of Fijian coral reefs by nonusers." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/29691.
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Thesis (Ph.D)--Public Policy, Georgia Institute of Technology, 2010.Committee Chair: Noonan, Douglas S.; Committee Co-Chair: Norton, Bryan; Committee Member: Bowman, Kirk; Committee Member: Fox, Mary F. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Savaro, Jennifer. "Connectivity of Reef Fishes Between Mangroves and Coral Reefs in Broward County, Florida." NSUWorks, 2015. http://nsuworks.nova.edu/occ_stuetd/378.
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Many marine fishes use the mangrove ecosystem for foraging, protection, spawning, and as a nursery habitat. To develop a better understanding of energy flow between the coastal mangrove and coral reef ecosystems, the ontogentic migration and trophic connectivity of reef fishes were examined through the use of carbon (C), nitrogen (N), and oxygen (O) stable isotope ratios. Juvenile and adult gray snapper Lutjanus griseus, lane snapper L. synagris, bluestriped grunt Haemulon sciurus, French grunt H. flavolineatum, sailor’s choice H. parra, yellowfin mojarra Gerres cinereus, and great barracuda Sphyraena barracuda were collected from both mangrove and coral reef sites located near Port Everglades, Broward County, Florida. All species were analyzed for δ13C and δ15N of muscle tissues and δ 18O and δ 13C of otoliths to evaluate ontogenetic migrations, foraging, and occupation within both the mangrove and reef sites. The δ13C and δ15N in muscle tissue were more depleted in juvenile fish from the mangroves than their adult forms caught on the adjacent reef. The δ18O and δ13C otolith data were significantly different between species, age class, and habitat, with lower δ18O values for juvenile fish caught in the mangroves. A general trend of increasing δ13C in otoliths corresponded to increasing total length, also suggesting juvenile movements from mangrove to nearshore reefs with age. Overall, the findings of this study further confirm that several commercially and recreationally important reef-associated fishes utilize mangrove ecosystems during juvenile life stages.
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Epstein, Nimrod. "Coral reefs aspects of management, conservation and restoration /." Amsterdam : Amsterdam : Universiteit van Amsterdam ; Universiteit van Amsterdam [Host], 2002. http://dare.uva.nl/document/62020.
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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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Lamb-Wozniak, Kathryn Amanda. "Nitrogen Cycling on Coral Reefs: A Stable Isotopic Investigation of Nutrient Dynamics within the Florida Keys Coral Reef Tract." Scholarly Repository, 2008. http://scholarlyrepository.miami.edu/oa_dissertations/23.
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This dissertation serves as a comprehensive, natural-abundance analysis of the present-day spatial and temporal dynamics and trophic linkages of nitrogen from within the Florida Keys National Marine Sanctuary (FKNMS). This work was accomplished by documenting the delta 15 N of particulate organic matter (POM), several genera of aquatic vegetation and herbivorous fish, as well as dissolved water column nitrogen. Seasonal and spatial variations in delta 15 N were assessed, trophic level variations among reef constituents were quantified, and relative contributions of both natural and anthropogenic nitrogen into the reef tract were determined. The measured mean delta 15 N of POM (3.64 per mil), aquatic vegetation (Dictyota = 2.39 per mil; Thalassia = 1.91 per mil; Rhizophora mangle = 1.46 per mil; Halimeda = 1.62 per mil; sponges = 4.13 per mil; turf algae = 2.67 per mil), herbivorous fish (4.92 to 8.47 per mil), as well as the delta 15 N and delta 18 O of nitrate (4.40 and 20.36 per mil, respectively) suggest that the primary nutrient sources directly impacting the reef are from natural sources, principally nitrogen fixation, and not anthropogenic wastes. Clear trophic linkages, without evidence of disturbances from anthropogenic wastes, are apparent in this study; herbivorous fishes show distinct 3 to 4 per mil enrichments over their food source. The presence of anthropogenic wastes was detected in the delta 15 N and delta 18 O of nitrate from Key Largo canal waters (10.09 per mil), however, sewage derived nutrients did not exist in any measurable or detectable amount outside the canals. Additionally, an assessment of the total yearly nitrogen contributions to the FKNMS was conducted, demonstrating that nitrogen fixation was the largest contributor of nitrogen to the ecosystem, delivering approximately 43 percent of all nitrogen. Anthropogenic wastes, however, contributed only about 8 percent to the total nitrogen budget, far less than biotic (non-human) wastes (13 percent), upwelling (10 percent), and gyre waters from the Gulf of Mexico (9 percent). For the first time, a long term, spatially diverse investigation has presented a more complete depiction of delta 15 N composition of various reef components found in the FKNMS, critical and imperative for accurately assessing nutrient pressures on coral reefs. As such, the data presented in this study do not support the theory that continuous anthropogenic nutrient loading from nearshore populations is the sole cause of reef decline in the FKNMS.
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Norström, Albert. "Upholding the coral loop : Resilience, alternative stable states and feedbacks in coral reefs." Doctoral thesis, Stockholms universitet, Systemekologiska institutionen, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-34037.
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Coral reefs are suffering unprecedented declines in coral cover and species diversity. These changes are often associated with substantial shifts in community structure to new dominant organisms. Ultimately, these “phase shifts” can be persistent and very difficult to return from. Building insurance against degradation and decreasing the likelihood of reefs undergoing shifts to undesirable states will require sustainable management practices that uphold coral reef resilience. This thesis consists of five papers that contribute new knowledge useful for managing the resilience of coral reefs, and other marine ecosystems. Paper I shows how the morphology of natural substrate (dead coral colonies) can significantly influence coral recruitment patterns. Paper II focuses on larval lipid levels, a key determinant of coral dispersal potential, in a common Caribbean coral (Favia fragum). It shows that i) lipid levels exhibit a significant, non-linear reduction throughout the larval release period of F. fragum and ii) exposure to a common pollutant (copper) could potentially lead to a more rapid lipid consumption in the larvae. Paper III presents a broader analysis of the different undesirable states a coral reef can shift to as a consequence of reef degradation. It concludes that different states are caused by different driving factors and that management must explicitly acknowledge this. Paper IV proposes a suite of resilience indicators that can help managers assess when a coral-dominated reef might be moving towards a shift to an undesirable state. These indicators capture key-processes occuring on different temporal and spatial scales and signal resilience loss early enough for managers to take appropriate measures. Finally, Paper V reviews the feedback loops that reinforce the undesirable states of five important marine ecosystems and suggests certain strategies that can ease the restoration back to healthier conditions. Managing these critical feedbacks will recquire monitoring the processes underpinning these feedbacks, breaking already established feedbacks loops through large-scale management trials and acknowledging transdisciplinary solutions that move management beyond the discipline of ecologyAt the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 5: In progress.
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Chaves-Fonnegra, Andia. "Increase of Excavating Sponges on Caribbean Coral Reefs: Reproduction, Dispersal, and Coral Deterioration." NSUWorks, 2014. http://nsuworks.nova.edu/occ_stuetd/5.
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Coral reefs ecosystems are deteriorating and facing dramatic changes. These changes suggest a shift in dominance from corals to other benthic organisms. Particularly in the Caribbean Sea, with corals dying, sponges have become the leading habitat-forming benthic animals. However, little is known about what life-history traits allow organisms to proliferate in a marine system that is undergoing change. Thus, the objective of this dissertation was to try to understand the current increase of encrusting excavating sponges on deteriorating Caribbean coral reefs through the study of reproduction, recruitment and dispersal potential of the widely distributed and currently expanding species, Cliona delitrix. Different methodological approaches were used, such as histology, electron microscopy, quantification of sponges in the field, genetics, and mathematical modeling. Results are presented in four different chapters. It was found that Cliona delitrix has an extended reproductive cycle in Florida, USA, from April - May to around November - December depending on a >25°C sea-water temperature threshold. C. delitrix gametogenesis is asynchronous and it has multiple spawning events. C. delitrix is recruiting abundantly on Caribbean coral reefs, preferentially on recent coral mortality than on old coral mortality. The increase in C. delitrix and other excavating sponges can be explained by the repeated spawning and by the coincidence in time and space of larval production with the availability of new dead coral, which tend to overlap during the warmest months of the year. Eggs or larvae of C. delitrix appear to survive enough to be transported by currents over larger distances. It was found that dispersal ranges for Cliona delitrix may reach as far as ~315 km in the Florida reef track, and over ~971 km in the South Caribbean Sea, between Belize and Panama. Thus, reproduction, dispersal, and recruitment patterns of C. delitrix along with oceanographic currents, and eddies that form at different periods of time, are sustaining the spread of this sponge on coral reefs. According to mathematical models carried out, C. delitrix increase on reefs fluctuates depending of coral mortality events and available space on old dead coral (colonized by algae and other invertebrates). However, under temperature anomalies, these sponges will 2 tend to increase and take over the reef system only if heat stress and coral mortality is moderate. Under massive mortality events both corals and sponges will tend to decline, although sponges at a slower rate than corals. In general, coral excavating sponges have been favored by coral mortality, especially during past few decades. However as bioeroders, their success is also limited by the success of calcifying corals. In a reef management context and based on this dissertation’s findings, it is suggested that excavating sponges, and especially Cliona delitrix, should be more formally included in reef monitoring programs. Their increase can be used to track coral mortality events on reefs (past and future), and also can be used as another major bioindicator of health on coral reefs.
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DeCarlo, Thomas Mario. "Coral biomineralization, climate proxies and the sensitivity of coral reefs to CO₂-driven climate." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/108899.
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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), 2017.Cataloged from PDF version of thesis.
Includes bibliographical references.
Scleractinian corals extract calcium (Ca²⁺) and carbonate (CO₃²⁻) ions from seawater to construct their calcium carbonate (CaCO₃) skeletons. Key to the coral biomineralization process is the active elevation of the CO₃²⁻ concentration of the calcifying fluid to achieve rapid nucleation and growth of CaCO3 crystals. Coral skeletons contain valuable records of past climate variability and contribute to the formation of coral reefs. However, limitations in our understanding of coral biomineralization hinder the accuracy of (1) coral-based reconstructions of past climate, and (2) predictions of coral reef futures as anthropogenic CO₂ emissions drive declines in seawater CO₃²⁻ concentration. In this thesis, I investigate the mechanism of coral biomineralization and evaluate the sensitivity of coral reef CaCO₃ production to seawater carbonate chemistry. First, I conducted abiogenic CaCO₃²⁻ precipitation experiments that identified the U/Ca ratio as a proxy for fluid CO₃²⁻ concentration. Based on these experimental results, I developed a quantitative coral biomineralization model that predicts temperature can be reconstructed from coral skeletons by combining Sr/Ca - which is sensitive to both temperature and CO₃²⁻ - with U/Ca into a new proxy called "Sr-U". I tested this prediction with 14 corals from the Pacific Ocean and the Red Sea spanning mean annual temperatures of 25.7-30.1 °C and found that Sr-U has uncertainty of only 0.5 °C, twice as accurate as conventional coral-based thermometers. Second, I investigated the processes that differentiate reef-water and open-ocean carbonate chemistry, and the sensitivity of ecosystem-scale calcification to these changes. On Dongsha Atoll in the northern South China Sea, metabolic activity of resident organisms elevates reef-water CO₃²⁻ twice as high as the surrounding open ocean, driving rates of ecosystem calcification higher than any other coral reef studied to date. When high temperatures stressed the resident coral community, metabolic activity slowed, with dramatic effects on reef-water chemistry and ecosystem calcification. Overall, my thesis highlights how the modulation of CO₃²⁻, by benthic communities on the reef and individual coral polyps in the colony, controls the sensitivity of coral reefs to future ocean acidification and influences the climate records contained in the skeleton.
by Thomas Mario DeCarlo.
Ph. D.
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Norström, Albert. "Upholding the coral loop resilience, alternative stable states and critical feedbacks in coral reefs /." Stockholm : Department of Systems Ecology, Stockholm University, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-34037.
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Diss. (sammanfattning) Stockholm : Stockholms universitet, 2010.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 5: In progress. Härtill 5 uppsatser.
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Mörk, Erik. "Macroalgal community dynamics on coral reefs : Implications for management." Doctoral thesis, Stockholms universitet, Systemekologiska institutionen, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-48281.
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Although rather inconspicuous on healthy coral reefs, macroalgae form the basis of coral food webs. Today, macroalgae are generally increasing and many reefs undergo transitions from coral to macroalgal dominance resulting from e.g. enhanced nutrient loading or increased fishing. This thesis aims to investigate the relative importance of top-down and bottom-up regulation, and different herbivore types, on macroalgal distribution, fecundity and community composition on coral reefs. Papers I and II indicate that macroalgal abundance in a coral reef system is largely governed by top-down regulation through grazing by herbivores, while bottom-up regulation through enhanced nutrient availability rather influence algal species composition. Paper II also shows that these regulating effects are not as evident in an area with relatively strong water motion, suggesting that impacts of anthropogenic disturbance may be site-specific. Paper III shows that herbivory is an important factor influencing macroalgal growth and subsequent reproduction. Furthermore, Paper IV and V conclude that efficiency in removing macroalgal biomass is dependent on the type of dominant herbivore, where sea urchins seem to be more effective than fish. Paper IV indicates a seasonal variation in macroalgal biomass and distribution in a small geographic scale but with relatively high temporal resolution. Paper V on the other hand shows these same effects, but with a focus on geographic variation, including a large part of the East African region, as well as between year temporal variations in Kenya. Together, results from the two latter studies indicate that herbivory by fish may not be able to prevent a macroalgal bloom in a degraded system where substrate availability for algal colonization is high, but that it may still facilitate coral recovery over time. Thus, a large algal biomass may not necessarily indicate a reef beyond the possibility of recovery.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Accepted. Paper 4: Manuscript. Paper 5: Manuscript.
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Gonzalez, Rivero Manuel Alejandro. "The ecology of bioeroding sponges on Caribbean coral reefs." Thesis, University of Exeter, 2011. http://hdl.handle.net/10036/3574.
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Sponges contribute to large number of functions in coral reef ecosystems. Among these, bioerosion is perhaps one of the most widely studied, largely due to the important contribution of excavating sponges to the carbonate budget on coral reefs (up to 95 % of the total internal bioerosion). Despite our current knowledge, much of the literature is centred on individual-based observations, and little is known about their ecological role and interactions with other reef taxa in complex coral reef systems. The aim of this thesis was to quantify the ecological interactions of bioeroding sponges with major reef taxa by scaling up individual observations to population and ecosystem-based approaches. A cosmopolitan, abundant and highly competitive bioeroding sponge from Glover’s Atoll, Belize (Cliona tenuis) was used as model species. Monitoring of C. tenuis populations throughout 2009 indicated a trade-off between reproduction and growth, with the highest growth rates (31.4 ± 5.6 mm.y–1) occurring in summer, and a peak in reproductive output during winter. Populations typically show strong left-skewed size frequency distributions, mostly represented by juvenile-size individuals (46%), suggesting that regulating mechanisms (e.g. competition and predation) may be acting in constraining the transition of juveniles to adult sizes. Long-term in situ manipulations showed no effect of predation, yet competition with macroalgae significantly reduced the size of the sponge by 38% ± 11% (SE). While C. tenuis exhibit high growth and recruitment rates that could theoretically result in rapid population growth, the likelihood of sponges forming an alternative stable state as reefs sustain greater levels of disturbance is unclear. An analytical modelling approach of the interplay between macroalgae, coral and sponge was used to explore the likelihood of alternate stable states. The results show that irrespective of successful sponge invasion, inclusion of this third antagonist (in the interplay between coral and macroalgae) can qualitatively affect the likelihood of alternative stable state. The model exhibits emergent properties suggestive of intransitivity between the three competing taxa. Despite the potential of C. tenuis to benefit from disturbance, there are few cases in the literature reporting increases in bioeroding sponge abundance followed disturbance. Therefore, regulating mechanisms such as competition with other taxa, recruitment limitation or mortality are expected to exert demographic control on the populations of bioeroding sponges when space limitation is relaxed due to coral mortality. To determine processes regulating sponge populations, an individual-based spatial modelling approach was used to simulate the population dynamics of C. tenuis in a dynamic ecosystem environment. Using an orthogonal hypothesis testing approach, it was found that competition, and to a lesser extend partial mortality of the sponge tissue, largely regulate the population structure of C. tenuis. While reductions in coral cover may temporarily favour the rapid colonization by sponges, the competitive superiority of macroalgae may steal the opportunity from the opportunists.
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Kwiatkowski, Lester. "Modelling environmental impacts on marine ecosystems and coral reefs." Thesis, University of Exeter, 2013. http://hdl.handle.net/10871/14931.
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Coral reefs are the iconic ecosystem of tropical seas and yet they are under increasing pressure as a result of multiple climatic stressors. This thesis uses observations and models to further understanding of environmental impacts on coral reefs. In particular it examines the impact of rising Sea Surface Temperature (SST) and ocean acidification on coral growth and the frequency of coral bleaching events. UK ocean biogeochemical models are assessed for implementation in the next UK Earth System Model. This analysis finds little evidence that more complex ocean biogeochemical models provide better simulations of large scale biogeochemical features. An established wavelet-based spatial comparison technique is used to analyse the spatial scales that Earth System Models can skillfully simulate patterns of SSTs. It is shown that in coral regions, current models cannot skilfully simulate patterns of historical SST anomalies at sub-regional (<32◦) scales. These findings are used in combination with SST and aragonite saturation state outputs from Earth System Models to show that historical Caribbean coral growth has been influenced by anthropogenic aerosol emissions over the 20th Century. Earth System Model outputs are also used to make projections of global coral bleaching throughout the 21st Century. It is shown that under even the most extreme conventional mitigation scenarios the majority of the world’s coral reefs are projected to experience levels of thermal stress induced bleaching that cause reef degradation throughout the 21st Century. Geoengeering scenarios involving the injection of SO2 into the stratosphere can reduce the projected thermal stress on coral reefs relative to conventional mitigation scenarios but such benefits are shown to be highly dependent on the sensitivity of coral bleaching thresholds to ocean acidification.
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Macdonald, Iain Andrew. "Reef growth and framework preservation in a turbid lagoon environment, Discovery Bay, North Jamaica." Thesis, Manchester Metropolitan University, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.288141.
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Edinger, Evan Nathaniel. "Effects of land-based pollution on Indonesian coral reefs : biodiversity, growth rates, bioerosion, and applications to the fossil record /." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0005/NQ42843.pdf.
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Bries, Jill M. "THE IMPACT OF HURRICANE LENNY ON CORAL REEFS AND ITS RELEVANCE TO PLEISTOCENCE REEF COMMNUNITIES: CURACAO, NETHERLANDS ANTILLES." University of Cincinnati / OhioLINK, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=ucin990629881.
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Slingsby, Shauna N. "Patterns of association and interactions between juvenile corals and macroalgae in the Caribbean /." Electronic version (PDF), 2003. http://dl.uncw.edu/etd/2003/slingsbys/shaunaslingsby.pdf.
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Klink, Lindsey Habakuk. "Review of International Coral Reef Mooring Programs and the Effect of Mooring Use on Coral Reefs Offshore Broward County, Florida, USA." NSUWorks, 2007. http://nsuworks.nova.edu/occ_stuetd/262.
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Coral reef communities are currently threatened by a variety of stressors. One direct and visible impact is physical damage from anthropogenic sources such as vessel anchors, recreational SCUBA divers, snorkelers, and debris. To lesson the impact of anchors on reefs, many coastal nations around the world have installed public mooring systems for use by small commercial and recreational vessel (typically less than 15 m in length). This thesis reviews current international mooring programs and assesses the impact of mooring use on reefs offshore Broward County, FL.
Details of existing mooring programs, such as costs, maintenance schedules, and effectiveness in meeting program goals, is not readily available to coral reef managers. In this study a questionnaire was distributed to obtain information about mooring programs worldwide. The 41 questionnaire respondents indicated that there is variability in operating and maintenance procedures. The vast majority of respondents viewed moorings as an effective and/or important management tool. Mooring programs are used to achieve a variety of management goals, often with the aid of additional regulations. Additional research is needed to determine if mooring programs are able to achieve the primary goal, as defined by the questionnaire respondents, of reducing anchor damage on coral reefs.
In this study, observations were conducted to determine mooring use offshore Broward County, Florida, USA. The majority of surveyed moored vessels were between 16 and 35 ft (4.8 and 10.6 m) in length. When all mooring site observations are pooled, SCUBA divers slightly outnumbered fishers as the primary users of the moorings; however, at some mooring sites fishing was more common than diving. Vessels were observed anchoring in the vicinity of the moorings even when moorings were available. Boater use patterns can aid in efficiently managing mooring maintenance and future resource management recommendations which may include additional regulations surrounding mooring use.
The effect of mooring use on coral reefs offshore Broward County, Florida, USA, was assessed through 20 m x 1.5 m belt quadrat transects. Three major groups of coral reef sessile organisms were surveyed: stony corals (Scleractinia), octocorals (Octocorallia), and sponges (Porifera). In total, 19 transects were sampled at mooring sites and 17 transects were sampled at adjacent, non-mooring reef sites. Sessile organisms located in the mooring transects did not show a significant difference in damage or number of unattached organisms when compared to nearby areas without moorings. Reef at mooring sites have a greater amount of debris than areas with no moorings. A comparison of the sessile communities at individual mooring sites indicated that the mooring site that was most heavily utilized by fishers had a greater amount of damaged octocorals and debris than the other mooring sites. Based on this study, moorings are having no effect on sessile organisms at the current level of use in Broward County. Although I was unable to measure an effect, I believe moorings to be a useful management tool. The presence of moorings has prevented thousands of anchor drops and I believe that if regulations are enacted to reduce the number of vessels anchoring near the moorings in Broward that the moorings could have a positive impact on the coral reef community.
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Webster, Jody Michael. "The response of coral reefs to sea level change: evidence from the Ryukyu Islands and the Great Barrier Reef." Thesis, The University of Sydney, 1999. https://hdl.handle.net/2123/28076.
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This thesis defines the response in two time frames, of individual reefs and coral reef ecosystems to sea-level change, through the bio-geological analysis of such reefs, on both active and passive margins. The raised Holocene reefs at Kikai-jima, Japan (Central Ryukyu Islands, ie. active margin) were examined for horizontal and vertical variation in exposed sections, and in drill core to determine the biological response of reefs to sea level fall. Holocene palaeoclimatic signals from a massive fossil coral at Kikai-jima were also investigated and their implications for reef growth and palaeoceanography discussed. Finally, two high-resolution cores from the Northern Great Barrier Reef (ie. passive margin) were examined to determine the biological response of reefs to repeated sea-level rise and fall over the last ~3 50 ky.
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Porter, Megan Ann. "Managing Coral Reefs in the Face of Global Climate Change: Developing a Coral Resilience Framework." Scholarly Repository, 2010. http://scholarlyrepository.miami.edu/oa_theses/287.
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Two experiments were performed to determine the effect of ocean acidification on Montastraea faveolata vertical skeletal growth and lesion healing. The first experiment used three different CO2 concentrations: present day atmospheric pCO2, 380 microatm, and the atmospheric pCO2 expected by the years 2050, 560 microatm, and 2100, 800 microatm. The second experiment used 380 and 560 microatm. In the second experiment where the influence of parent colony was analyzed, M. faveolata fragments from one coral colony had significantly slower skeletal growth rates and less healed lesion area than other colonies. Corals that calcify and regenerate tissue slower may have less resilience to ocean acidification. The experiments demonstrated that the corals in 800 microatm grew significantly slower than corals in 380 or 560 microatm. Increased CO2 concentrations increased M. faveolata skeletal growth rates and healed lesion area until a threshold was reached, 560 microatm, then growth rates and healed lesion area decreased. Less than 1% of the variability in healing rates could be explained by CO2. The Nature Conservancy Resilience Model was used as a framework to identify current management strategies of wider Caribbean MPAs that may increase coral reef resilience to climate change. Seven out of the 8 MPAs had representation, critical areas, connectivity, and effective management as determined by each MPA's management plan. Three management plans had specific climate management strategies. Each management plan had actions to build coral reef resilience, but institutional incapacities and other barriers can decrease the ability to increase reef resilience. Because of the weaknesses of the Resilience Model, revised resilience guidelines were developed with the Florida Keys National Marine Sanctuary (FKNMS) as a case study. The coral lesion experiment results and interviews with FKNMS managers and the FKNMS's Sanctuary Advisory Council helped design the revised resilience guidelines. The revised climate-based coral reef resilience guidelines are to 1) incorporate more no-take zones and hedge the risks against ocean acidification, 2) identify resilient coral reefs and perform more climate change research, 3) reduce local stressors, 4) enhance coral reef recovery, and 5) increase public awareness and education on climate change impacts to coral reefs.
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Faxneld, Suzanne. "Coral reefs in the Anthropocene : The effects of stress on coral metabolism and symbiont composition." Doctoral thesis, Stockholms universitet, Systemekologiska institutionen, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-62867.
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Coral reefs constitute some of the most prolific and diverse ecosystems on our planet, but also among the most threatened. This thesis investigates the effects of environmental stressors on corals’ metabolism and symbiont diversity. Paper I shows that the coral Turbinaria mesenterina withstood a single stressor while a combination of two stressors (decreased salinity and increased seawater temperature) lead to decreased metabolism. Increased seawater temperature in combination with two stressors (enhanced nutrients and decreased salinity) lead to rapid mortality of all specimens. Paper II shows that chronic stress in combination with increased seawater temperature affects coral species differently. Porites lutea did not show any difference in response to temperature increase, regardless of environmental disturbance history, while Galaxea fascicularis’ metabolism was negatively affected in chronically disturbed corals but not in corals from less disturbed areas. The main explanation for the difference in response between the two species is different compositions of endosymbionts as found in paper III. P. lutea only harboured the symbiont C15, regardless of environment, whilst D1a dominated the nearshore G. fascicularis and C1 dominated offshore corals. In paper IV there was a clear inshore-offshore pattern of D1a along the whole coast of Vietnam, where D1a dominated inshore. In contrast, the five symbionts belonging to group C displayed a strong latitudinal gradient, with diversity increasing from north to south. The coral host showed higher diversity offshore than inshore. The thesis emphasizes the importance of improving water quality (paper I and II) and protecting marginal areas since tolerant coral hosts and symbionts can be found there (paper III and IV), as well as safeguarding areas with high symbiont diversity (paper IV) to increase the ability of corals to withstand future environmental changes.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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Gustafson, Steven K. "Assessment of Image Analysis as a Measure of Scleractinian Coral Growth." Scholar Commons, 2006. http://scholarcommons.usf.edu/etd/3768.
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Image analysis was used to measure basal areas of selected colonies of Montastraea annularis and Porites astreoides, following the colonies over a three-year period from 2002 to 2004. Existing digital images of permanently-marked quadrats in the Caye Caulker Marine Reserve, Belize, were selected based on image quality and availability of images of selected quadrats for all three years. Annual growth rates were calculated from the basal-area measurements. Mean growth rates (radial skeletal extension) for M. annularis and P. astreoides were 0.02 cm yr-1 and -0.20 cm yr-1, respectively. Basal area measurements demonstrated a large degree of variability. Increases were approximately balanced by declines giving the impression of stasis. By removing negative values and correcting by 25% to allow for comparison with vertical growth rates, mean values increased to ~0.5 cm yr-1 for M. annularis and ~0.8 cm yr-1 for P. astreoides.
Basal area as a growth measure was compared to methods used in earlier studies. A new growth index based on basal area and perimeter was proposed and modeled. This growth index can be useful for reporting growth measured from basal areas and comparable other methods. The index also measures negative growth, or mortality, which conventional methods cannot do.
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Rubin, Ewelina. "Scleractinian Coral Recruitment to Reefs Physically Damaged by Ship Groundings." NSUWorks, 2009. http://nsuworks.nova.edu/occ_stuetd/227.
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Southeast Florida reefs are impacted by a number of stress factors, among which ship groundings are one of the most physically damaging. In particular, portion of Florida reef tract located near Port Everglades in Broward County has been severely damaged by ship groundings. In 2004, extensive physical damage of more than 30,000 m2 was caused by the groundings of two large cargo ships, the MV Eastwind and MV Federal Pescadores. The present study was designed to examine differences in the recruitment patterns of scleractinian corals and pioneering benthic communities settling to these physically impacted sites compared to undamaged reef sites. Coral recruitment and non-coral benthic settlers were measured on unglazed terracotta tiles deployed for a period of one year from February 2007 to February 2008 at five different locations: three control sites (including a high coral cover site) and the two ship grounding sites. Colony morphology and two genetic markers: mitochondrial cytochrome oxidase subunit I and cytochrome b were used to identify the coral recruits. A whole genome amplification kit (REPLI-g, Qiagen) was used to obtain sufficient amounts of DNA from small coral spat. The image analysis software Coral Point Count with the Excel extension was used to quantify the percent cover of major benthic invertebrate and algal functional groups. Results revealed very low diversity of coral recruits and low recruitment rates (0.5-2.7 recruits m-2 yr-1), suggesting a low potential for recovery of the damaged areas. Other non-coral benthic groups, including turf algae, barnacles, sponges, tunicates and bryzoans, were found to proliferate and occupy almost the entire tile substrate, suggesting possible coral recruitment inhibition by space preemption or coral recruit mortality by overgrowth. Turf algae which comprised up to 50% of the total cover were the most dominant group settling to the tiles. This dominance of algae on the tiles reflects a similar pattern of algal dominance present on the reef system along the Florida coast.
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Nordemar, Ingrid. "Human Abuses of Coral Reefs- Adaptive Responses and Regime Transitions." Doctoral thesis, Stockholm : Institutionen för systemekologi, Univ, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-250.
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Rasher, Douglas B. "Chemically mediated competition, herbivory, and the structure of coral reefs." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/49019.
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Corals, the foundation species of tropical reefs, are in rapid global decline as a result of anthropogenic disturbance. On many reefs, losses of coral have coincided with the over-harvesting of reef herbivores, resulting in ecosystem phase-shifts from coral to macroalgal dominance. It is hypothesized that abundant macroalgae inhibit coral recovery and recruitment, thereby generating ecological feedback processes that reinforce phase-shifts to macroalgae and further diminish reef function. Notwithstanding, the extent to which macroalgae directly outcompete coral, the mechanisms involved, and the species-specificity of algal-coral competition remains debated. Moreover the capacity for herbivores to prevent vs. reverse ecosystem phase-shifts to macroalgae and the roles of herbivore diversity in such phenomena remain poorly understood. Here I demonstrate with a series of field experiments in the tropical Pacific and Caribbean Sea that multiple macroalgae common to degraded reefs directly outcompete coral using chemical warfare, that these interactions are mediated by hydrophobic secondary metabolites transferred from algal to coral surfaces by direct contact, and that the outcomes of these allelopathic interactions are highly species-specific. Using field observations and experiments in the tropical Pacific, I also demonstrate that the process of herbivory attenuates the competitive effects of allelopathic algae on corals by controlling succession of algal communities, and that the herbivore species responsible for macroalgal removal possess complementary tolerances to the diversity of chemical defenses deployed among algae, creating an essential role for herbivore diversity in reversing ecosystem phase-shifts to macroalgae. Lastly, I demonstrate with field experiments in the tropical Pacific that algal-coral competition simultaneously induces allelochemicals and suppresses anti-herbivore deterrents in some algae, likely due to trade-offs in the productions of defense metabolites with differing ecological functions. Together, these studies provide strong evidence that chemically mediated competitive and consumer-prey interactions play principal roles in coral reef degradation and recovery, and should provide resource managers with vital information needed for effective management of these ecologically and economically important but threatened ecosystems.
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Galford, Gillian, Margarita Fernandez, Roman Joe, Irene Monasterolo, Sonya Ahamed, Greg Fiske, Les Kaufman, and Patricia Gonzalez-Diaz. "Cuban land use and conservation, from rainforests to coral reefs." Rosenstiel School of Marine and Atmospheric Science, University of Miami, 2018. http://epub.wu.ac.at/6405/1/s3.pdf.
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Cuba is an ecological rarity in Latin America and the Caribbean region. Its complex political and economic history shows limited disturbances, extinctions, pollution, and resource depletion by legal or de facto measures. Vast mangroves, wetlands, and forests play key roles in protecting biodiversity and reducing risks of hazards caused or aggravated by climate change. Cuba boasts coral reefs with some of the region's greatest fish biomass and coral cover. Although it has set aside major protected areas that safeguard a host of endemic species, Cuba's environment is by no means pristine. Through much of its early history, deforestation and intensive agricultural production under colonial then neocolonial powers was the norm. Using remote sensing, we find Cuba's land today is 45% devoted to agricultural, pasturage, and crop production. Roughly 77% of Cuba's potential mangrove zone is presently in mangrove cover, much of it outside legal protection; this is likely the most intact Caribbean mangrove ecosystem and an important resource for coastal protection, fish nurseries, and wildlife habitat. Even the largest watersheds with the most agricultural land uses have a strong presence of forests, mangroves, and wetlands to buffer and filter runoff. This landscape could change with Cuba's gradual reopening to foreign investment and growing popularity among tourists-trends that have devastated natural ecosystems throughout the Caribbean. Cuba is uniquely positioned to avoid and reverse ecosystem collapse if discontinuities between geopolitical and ecosystem functional units are addressed, if protection and conservation of endemic species and ecosystems services accompany new development, and if a sound ecological-restoration plan is enacted.
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Young, Grace C. "Three-dimensional modelling of coral reefs for structural complexity analysis." Thesis, University of Oxford, 2017. http://ora.ox.ac.uk/objects/uuid:cde6d4fd-a2a6-4d31-b37c-adca785dc614.
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Coral reefs are some of Earth's most biodiverse and economically valuable ecosystems. Simultaneously they are among the most threatened by anthropogenic factors including global climate change. Their unique three-dimensional (3D) structural complexity is part of what enables them to provide their ecosystem services. It strongly affects species richness, abundance, and other indicators of ecosystem health. This thesis explores the relationship between coral reef 3D structural complexity and ecosystem features. It has developed a new, low-cost method for creating and analysing photogrammetric 3D models of shallow reefs from diver-held camera footage. 3D models are analysed at scales 1-175 cm in terms of point-to-point distances, linear rugosity (R), fractal dimension (D), and vector dispersion (1/k). The 3D models' accuracy and precision were determined by comparisons with ground truths. The 3D models have root mean square errors of 1.35-1.48 cm in the X, Y and Z dimensions. Values of R from the 3D models were 86.8% accurate compared to in-situ chain-and-tape measurements. Values of D and 1/k were 86.9-99.6% accurate compared with ground truths from 3D printed objects modelled underwater. Data collected around Utila, Bay Islands, Honduras in the Caribbean showed that 3D metrics automatically calculated from the 3D models had the same predictive power for fish abundance and diversity as the more traditional Habitat Assessment Score (HAS). Like HAS, the 3D metrics explained 12-34% of variation in the fish data. A controlled experiment furthermore tested how 1/k affected sessile epibenthic organism settlement around Utila after one year. Results from approximately 200 3D printed recruitment tiles showed that 1/k significantly affected algae settlement, but not coral spat, polychaete, sponge, or bryozoan settlement. The results suggested that the surfaces of artificial reefs can be designed to minimise algal recruitment and that the availability of sheltered, reef-facing area influences epibenthic settlement more strongly than 1/k at the 1 cm scale. Finally, a convolutional neural network (CNN) learned patterns between the 3D models and fish data with just 85 data points. The CNN is a promising approach for analysing larger data sets without 3D metrics. We suggest 3D models become a standard approach for measuring reef structural complexity. Not only can they explain as much variation in fish abundance and diversity as traditional measurements, but also they can nondestructively produce a variety of 3D metrics at numerous spatial scales and keep a permanent record of reef structure over time.
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Andersson, Maria, and Mikaela Ring. "The Need for Permanent Mooring Buoys in the Gulf of Thailand : A Minor Field Study." Thesis, KTH, Industriell ekologi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-139383.
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The purpose of this paper is to evaluate the need for permanent mooring buoys at the popular off-shore islands of Pattaya, Thailand. By investigating the ecological, social and economic gains and losses of installing such buoys, the project aims to examine whether such buoys would help support a more sustainable development in the area. In order to fulfil the aims and objectives of the project, a literature study, two different questionnaires, interviews, line intercept transects (LIT) and a boat traffic survey were performed. The results prove that every dive store operator, 71% of the dive instructors/dive masters and 65% of the tourist divers that took part in the interviews or questionnaires have observed anchor damages in the area. This is supported by the results of the LITs, which, although differing greatly between depths, reveal a top score of 44% damaged corals (of which 20% were apparent anchor damages) at snorkelling depth at site 3. At diving depth the damage indexes were generally lower, revealing a top score of 38% damaged corals at Site 2, but no definite anchor damages. The boat traffic survey showed that 192 boats were active in the area, of which 47 used an anchor, during a 3 hour period a Saturday morning. The results also prove that dive store operators and questionnaire participants generally agree that divers wish to see healthy reefs and great aquatic biodiversity when visiting a dive site. The interviews showed that all dive store operators have a positive attitude towards an installation of mooring buoys in the area, which could protect the local reefs and thereby their own business. 85% of the tourist divers that took part in the questionnaires stated they would be willing to pay extra (where a majority of those with a WTP would be willing to pay 7-13 USD) if they could be guaranteed to see healthy coral reefs and a great diversity in species and 88% stated they would be willing to pay extra (where a majority of those with a WTP would be willing to pay 0.7-1.7 USD) to support a permanent mooring buoy system. The interviews and the questionnaires also prove that healthy coral reefs hold a special sentimental value, providing invaluable recreational opportunities to humankind. Conclusively the results indicate that there is a need for permanent mooring buoys in the area. The ecological, social and economic gains of installing permanent mooring buoys seem to overshadow the cost of installation and maintenance of the buoys, meaning the buoys would most certainly improve the conditions for a more sustainable development in the area.
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Scheffers, Sander R. [Verfasser]. "Benthic-Pelagic Coupling in Coral Reefs: Interaction between Framework Cavities and Reef Water / Sander R Scheffers." Aachen : Shaker, 2005. http://d-nb.info/1186577347/34.
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Swanson, Dione W. "Spatial Dynamics of Coral Populations in the Florida Keys." Scholarly Repository, 2011. http://scholarlyrepository.miami.edu/oa_dissertations/626.
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Coral reef degradation has been observed worldwide over the past few decades resulting in significant decreases in coral cover and abundance. However, there has not been a clear framework established to address the crucial need for more sophisticated understanding of the fundamental ecology of corals and their response to environmental stressors. Development of a quantitative approach to coral population ecology that utilizes formal, well established principles of fishery systems science offers a new framework to address these issues. The goal of this dissertation is to establish a quantitative foundation for assessment of coral reefs by developing some essential ecological and population-dynamic components of a size-structured demographic model for coral populations of the Florida Keys coral reef ecosystem. The objective provides the potential to build a quantitative systems science framework for coral populations. A two-stage stratified random sampling design was implemented during two separate survey periods to assess coral populations. Results include precise estimates of adult (> 4 cm) population abundance for several coral species by spatially partitioning abundance and variance into species-relevant reef habitat types. Adult size structure and juvenile abundance were used to evaluate individual coral populations and infer spatial variation in recruitment, growth and survival across habitat types. Partial mortality was characterized in terms of surface area, prevalence, and size-relationships. The development of some ecological and population-dynamic components of a size-structured demographic model for coral populations demonstrates the statistical framework and metrics required for monitoring and assessment of coral reef ecosystems to meet the pressing needs of conservation of coral reef ecosystems specifically in Florida, and throughout the Caribbean and Pacific in general.
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Humphries, Austin Turner. "Fishing for resilience : herbivore and algal dynamics on coral reefs in Kenya." Thesis, Rhodes University, 2014. http://hdl.handle.net/10962/d1013147.
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Herbivory is a key process that mediates the abundance of primary producers and community composition in both terrestrial and aquatic ecosystems. On tropical coral reefs, changes in herbivory are often related to phase shifts between coral-dominance and dominance by seaweeds, or foliose macroalgae. Resilience or capacity to resist and reverse such phase shifts is, therefore, viewed as a critical function on coral reefs. This thesis used grazer exclusion and assay experiments at six sites within three different fisheries management regimes in Kenya to identify the impacts of herbivores (sea urchins and fishes) on algal dynamics in the context of coral reef resilience. First, I examined the grazing rates necessary to prevent phase shifts by quantifying consumption and algal production. Here, I found that, over a 390-day experiment, at least 50 percent of algal production must be consumed to avoid accumulation of algal biomass. Using video observations, I also showed that scraping parrotfishes remove more algae (per unit of fish biomass) than previously assumed, and that sea urchins, if released from predation, have similar impacts to fishes. Then I focused on algal succession, and found that sea urchins and fishes have different effects that are mediated by their abundances and species composition. Where sea urchins were less abundant and parrotfishes absent (e.g. young fisheries closures), progression of algae from turfs to early and then late successional macroalgae occurred rapidly and within 100 days. I then turned my focus to the removal of already established macroalgae (grown for > 1 yr in the absence of herbivores) and showed that sea urchins and browsing fishes were able to remove significant amounts of macroalgae where either herbivore was abundant. However, using multiple-choice selectivity assays and in situ video recordings, I found that browsing fishes fed very selectively with low overlap in diet among species, leading to low functional redundancy within a high diversity system. Finally, using long-term survey data (from 28 sites) to build a 43-year chronosequence, I showed that it is possible that the effects of herbivory will not be constant across transitions from open fishing to fishery closures through non-linear grazing intensity. Therefore, increases in herbivory within fisheries closures may not be immediate and may allow a window of opportunity for algae to go from turf to unpalatable macroalgae until scraping and browsing fishes fully recover from fishing (~ 20 years). The findings in this thesis are novel and raise concern over the potential implications of the slow recovery of parrotfishes or, given lower than expected functional redundancy in grazing effects, the absence of even one browsing fish species in fisheries closures. Overall, this thesis highlights the importance of herbivore community dynamics in mediating interactions among algae, and provides new insights for conservation and management actions that attempt to bolster the resilience of coral reefs.
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Joyce, Karen E. "A method for mapping live coral cover using remote sensing /." [St. Lucia, Qld.], 2004. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe18618.pdf.
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Hagman, Derek Kristian. "Reproductive dynamics of coral reef biota at the Flower Gardens /." Full text (PDF) from UMI/Dissertation Abstracts International, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3008347.
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Da, Silva Costa Ozeas. "Nutrification and its effects on coral reefs from Southern Bahia, Brazil." Thesis, University of Plymouth, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.392601.
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Hawkins, Julie P. "Impacts and management of fisheries and tourism on Caribbean coral reefs." Thesis, University of York, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.423840.
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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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Cooper, Timothy F. "Coral bioindicators of environmental conditions on coastal coral reefs." Thesis, 2008. https://researchonline.jcu.edu.au/8170/1/01Front.pdf.
Full textAbstract:
Reversing the decline in water quality is a key priority for the protection of the Great Barrier Reef (GBR). Strategies to improve the water quality of the GBR include conservation of riparian zones and the adoption of ecologically sustainable practices in the catchments. The implementation of these strategies requires feedback to resource managers and the community through monitoring programmes aimed at detecting biological responses to changes in water quality. This thesis investigates a range of coral indicators at different spatial and temporal scales and identifies those most suitable for inclusion into a toolbox for monitoring the condition of coastal coral reefs on the GBR. The approach combines in situ studies of coral indicators in different regions and environmental gradients on the GBR with controlled manipulative experiments exposing corals to differing water quality to examine causality of correlations observed in the field.
An environmental gradient was identified in the Whitsunday Islands where water column variables (especially chlorophyll a, total suspended solids, particulate organic carbon and particulate nutrients) and irradiance variables (Secchi and optical depth) differed significantly from nearshore to the outer islands. For example, mean concentrations of chlorophyll a were up to 1.9 times greater at nearshore (Repulse Island; RI: 0.59 ± 0.12 μg L-1 mean ± SE) compared with outer islands (Edward Island; EI: 0.31 ± 0.06 µg L-1) averaged over five sampling events from 2004 to 2006, whereas mean Secchi depth was approximately 3 times lower at nearshore (RI: 4.0 ± 0.8 m) than outer locations (EI: 15.3 ± 3.3 m). Some of the coral indicators showed significant relationships with a water quality index (WQI) derived for the Whitsunday Islands. Responses of photo-physiological measures of Symbiodinium associated with Pocillopora damicornis along the gradient were consistent with patterns of light acclimatisation and suggested deep corals (i.e. below 5 – 6 m depth) on nearshore reefs in the Whitsunday Islands are light-limited. Both colony brightness and tissue thickness of massive Porites spp., and the maximum depth of reef building corals, increased from nearshore to outer locations along the gradient. Similarly, a 50-fold decrease in the density of macro-bioeroders in massive Porites from nearshore to outer locations was indicative of increased particle loads on the nearshore reefs. The data of the maximum depth limit for coral reef development at locations where suitable settlement substrata were available suggest that the absolute minimum of light required for a coral reef to persist is in the range of 6 – 8 % of surface irradiance in the Whitsunday Islands.
The model that color brightness of corals responded to changes in water quality was validated with manipulative experiments in the laboratory and by transplantation of small nubbins along the environmental gradient. The experiments showed nubbins of massive Porites became darker, i.e. concentrations of pigments increased, within 20 – 40 days of exposure to elevated nutrients and reduced irradiances compared with corals kept in filtered sea water and unshaded conditions. The response in colony brightness was consistent with other studies of photo-acclimatisation to enhanced nutrients and light limitation. However, a 2.5-fold decrease in symbiont density of P. damicornis during the wet compared with the dry season, which in turn influenced colony brightness, was related strongly to seasonal changes in sea surface temperature (SST). Thus, effects of seasonal variation of a range of environmental parameters need to be considered if physiological measures such as colony brightness are used in water quality monitoring programmes.
The simultaneous in situ measurement of benthic irradiance and turbidity at a shallow depth (~3.5 m) on a coastal coral reef for 2 years allowed the quantification of potential thresholds of concern for turbidity. The linear relationship between the attenuation coefficient for downward irradiance Kd (PAR) and turbidity showed that a change from 0 to 3 nephelometric turbidity units (NTU) at 3.5 m results in a decrease of 88% of benthic irradiance to levels around 200 µmol photons m-2 s-1. The minimum saturating irradiance (Ek) of Symbiodinium associated with P. damicornis was approximately 206 ± 8 µmol photons m-2 s-1 at shallow depths on nearshore reefs of the Whitsunday Islands. Thus, levels of turbidity greater than 3 NTU can result in environmental conditions that are light limiting, and hence sublethal photo-physiological stress, for P. damicornis. Levels of turbidity of 4.5 NTU corresponded to 6 – 8% of surface irradiance, which was a critical level of irradiance required for coral reef development in the Whitsunday Islands. Thus, long-term turbidity >3 NTU could be used as a threshold of turbidity for sublethal photo-physiological stress, while long-term turbidity >5 NTU for severe stress effects on P. damicornis at shallow depths (~3.5 m) on coastal reefs.
Temporal variation in the growth parameters of massive Porites from two nearshore regions of the GBR were not consistent with regional differences in water quality. Mean annual SST increased by ~0.38°C over a 16 year study period that correlated with a decline of ~21% in coral calcification rates. A decline in calcification of this magnitude with increasing SST contrasts with results of previous studies and is unprecedented in recent centuries. Changes in the growth parameters were linear over time, while SST had no effect on skeletal density, but a modal effect on annual extension and calcification with maxima at ~26.7°C. The findings were consistent with other experimental studies of the synergistic effect of elevated seawater temperatures and CO2 partial pressure (pCO2) on coral calcification and suggest that monitoring of seawater chemistry should be undertaken on the GBR.
Defining a set of key selection criteria and assessing the characteristics of candidate indicators in a matrix against changes in water quality, allowed the identification of coral indicators for a monitoring toolbox. The most suitable bioindicators were: symbiont photo-physiology, colony
brightness, skeletal and tissue growth, and bioeroder density in massive Porites, coral recruitment, community structure of corals, indicator organisms other than corals and the maximum depth of coral reef development. As each of these measures has a different sensitivity and response time to changes in environmental conditions, a combination of measures, i.e. a composite indicator system, is recommended for use in assessments of the condition of coastal reefs on the GBR.
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Stępień, Anna. "Tanaidacea (Crustacea:Peracarida) of Australian coral reefs." Phd diss., 2015. http://hdl.handle.net/11089/6479.
Full textAbstract:
Tanaidacea are group of marine benthic crustaceans classified to Malacostraca.
Currently over 1200 species are described. However it is supposed that the number of
known species constitute 2-3% of estimated 4000 species.The main aim of the thesis was to estimating biodiversity of Tanaidacea from
Australian coral reefs. Material was collected during CReefs program, being part of the
bigger Census of Marine Life. Goal of the CReefs program was to increase knowledge
about diversity of coral reefs. In 2008–2010 scientific expedition were organized to
Lizard Island (Northern Great Barrier Reef), Heron Island (Southern GBR) and
Ningaloo Reef (Western coast).Metapseudidae and Leptocheliidae are the most rich in species families. Nine
species, three genera and one subfamily classified to the Leptocheliidae are described
and illustrated. Beyond that the genus Synapseudes (Metapseudidea) are revised. Species
classified to the genus present morphological heterogeneity, thus some scientist suggest
division the genera. Phylogenetic analysis and Principal Component Analysis indicate
that vast majority of the species can be classifies to the Synapseudes. Only one species
S. idios should be transformed to the distinct genera.Skorupiaki z rzędu kleszczug (Tanaidacea) to typowo morskie organizmy zaliczane do pancerzowców właściwych (Malacostraca), zasiedlające praktycznie wszystkie znane morskie habitaty denne. Obecnie znanych jest ponad 1200 gatunków kleszczug. Uznaje się jednak, że liczba opisanych gatunków stanowi zaledwie 2–3% spośród szacowanych 4000 gatunków.Nadrzędnym celem niniejszej rozprawy doktorskiej jest ocena różnorodności biologicznej skorupiaków z rzędu Tanaidacea raf koralowych Australii. Materiał badawczy został zebrany w trakcie programu Census of Coral Reefs Ecosystem (CReefs), jednego z programów Census of Marine Life (CoML), poświęconego badaniom różnorodności biologicznej raf koralowych. Do najróżnorodniejszych pod względem gatunkowym należały rodziny Metapseudidae Lang, 1970 i Leptocheliidae Lang, 1973. Dziewięć gatunków, trzy nowe rodzaje oraz nowa podrodzina zaklasyfikowane do Leptocheliidae zostały opisanie i zilustrowanie. Ponadto rewizji poddano rodzaj Synapseudes (Metapseudidae).Analiza filogenetyczna i analiza głównych składowych (PCA) wykazały, że znacząca większość gatunków może być klasyfikowana do rodzaju. Jedynie Synapseudes idios powinien reprezentować odrębny rodzaj.
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Whinney, James Christopher. "Physical conditions on marginal coral reefs." Thesis, 2007. https://researchonline.jcu.edu.au/2063/1/01front.pdf.
Full textAbstract:
The Great Barrier Reef Lagoon (GBRL) is an area of great biodiversity containing 350 species of corals, 10 of which are endemic to the region. In recent years many threats to this ecosystem have been revealed, such as crown-of-thorns starfish and coral bleaching as well as excess concentrations of nutrients and sediments. Information on the effects of water quality and also the amounts of nutrients and sediments that reefs are subjected to is limited. This is especially true for inshore reefs where issues of water quality are most important.
This work focuses on the Rockingham Bay and Family Islands region. In this region a reef in Lugger Bay near Mission Beach was selected for a detailed study. It is a highly marginal reef (a reef occurring close to perceived environmental thresholds for coral survival) with high levels of sediments and organic matter and close to the mouths of two rivers: the Tully and the Hull. This makes the reef one of the most at threat from eutrophication and increases in sediment. Part of this work was to document all the physical conditions of the reef including currents, wind speed and direction, light levels, temperature, nutrients, and suspended sediment concentration (SSC). The reef’s health and age were also found by means of photographic surveys and core samples respectively.
The main results from the study showed a reef surviving in extreme physical conditions. The SSC on the reef were very high, exceeding 200 mg/l for 28% of the time. Light extinction was common, occurring on 49% of the days that data was recorded. The local rivers did not have much effect on the SSC or nutrient concentrations on the reef. The Tully River only has a wet-season average SSC of 23 mg/l and a maximum of 230 mg/l; resuspension was much more significant. Coral cover on the reef was reasonable, about 57%, and algae only covered 12% of the coral. However, coral species biodiversity was low, with one species of Porites making up 85% of the coral cover. These results indicate that some species of coral are able to survive in areas of high sediment and nutrient concentrations, and that clean rivers in the GBRL are not a great threat to coral reefs.
The SSC data was also used to develop an empirical model, which predicts SSC for a specific site using just wind data. The model is accurate enough to be used in environmental monitoring to predict an expected SSC, which can be prepared with observed SSC from a site where marine construction is taking place so it can be determined whether the work has increased the SSC to a dangerous level. This makes it an important tool as many such construction projects occur in the GBRL each year and there is no other accurate method of determining what the natural SSC would be if work was not taking place.
A new instrument was also developed to infer nutrient concentrations in the water column, to try to overcome problems with existing methods. The instrument works by measuring the speed at which algae grow on a glass plate using a fluorometer. Tests were made to determine how well algal growth would relate to nutrient concentrations, if other factors like temperature, light levels and algal type were not controlled. Results showed that growth was too dependent on these other factors to be a good indicator of nutrient concentrations. The sensor could, however, be used to determine the effect nutrients have on algal growth, which in itself is a potential threat to corals.
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Ban, Stephen Shigeyoshi. "Multiple stressor effects on coral reefs." Thesis, 2014. https://researchonline.jcu.edu.au/40712/1/40712-ban-2014-thesis.pdf.
Full textAbstract:
Coral reef ecosystems around the world face a number of threats, including ocean acidification, increased ocean temperatures due to anthropogenic global warming (AGW), increased disease outbreaks, crown-of-thorns starfish outbreaks, terrestrial sedimentation, eutrophication, pollution, and fishing pressure. At the same time, coral reef ecosystems provide valuable direct and indirect economic and social benefits to millions of people worldwide. However, the intensity and spatial distribution of threats are likely to change with increasing human population and economic development, and thus understanding how multiple stressors may interact and affect coral reefs – particularly in the face of incomplete knowledge about these stressors – is an issue of pressing importance.
This thesis aims to explore and advance the understanding of interactions between multiple stressors and their effects as they pertain to coral reefs generally and the Great Barrier Reef specifically. I review several of the components that are integral to this issue, including: stressors and stress ecology, research to date on the issue of multiple stressors and coral reefs, the multiple threats from climate change to coral reefs, and approaches to modelling and managing multiple stressors.
The overall aim of this thesis is to quantitatively evaluate the importance of multiple stressor interactions to coral reef ecosystems and to assess alternative management approaches to mitigating the effects of potentially increased prevalence and severity of these stressors. I do this through both assessing the state of existing knowledge as well as by using new approaches to model stressors and stressor effects within the context of the GBR. In addition, I seek to provide an example of how these effects can be conceptualized and managed more effectively in the face of uncertain knowledge and incomplete data.
The specific research objectives of my thesis are as follows:
1. To synthesize the available knowledge of multiple stressors on coral reefs;
2. To use the occurrence of bleaching and disease in the GBR as a case study to determine the spatial and temporal overlap of these stressors;
3. To use expert knowledge to identify key uncertainties and knowledge gap(s) regarding multiple stressor interactions on coral reef systems;
4. To apply expert-elicited knowledge about stressors and stressor interactions on the GBR to map potential threats to reefs under a variety of different climate change and management scenarios.
Chapter 2 addresses research objective 1 by using a formal literature search to provide the foundation for a qualitative and selected quantitative meta-analysis of multiple-stressors as they pertains to coral reef ecosystems, and by examining the evidence for the prevalence of synergistic, antagonistic, and additive interactions between stressors. Here I investigate stressor interactions in two ways: first by examining stressor interactions with other stressors, and secondly by looking at potentially synergistic effects between two or more stressors on a response variable (where stressors interact to produce an effect that is greater than purely additive). For stressor-stressor interactions, I found 176 studies that examined interactions between at least two stressors. Applying network analysis to analyse relationships between stressors, I found that pathogens were exacerbated by more co-stressors than any other stressor, while sedimentation, storms, and water temperature directly affected the largest number of other stressors. Pathogens, nutrients, and crown-of-thorns starfish were the most-influenced stressors. In terms of responses to multiple stressors, I found 187 studies that examined the effects of two or more stressors on a third dependent variable. The interaction of irradiance and temperature on corals has been the subject of more research than any other combination of stressors, with many studies reporting a synergistic effect on coral symbiont photosynthetic performance. Second, I performed a quantitative meta-analysis of existing literature on the interaction between temperature and irradiance. Although the sample size was small, I found that the mean effect size of combined treatments was statistically indistinguishable from a purely additive interaction. This chapter provides evidence that considerable gaps remain in our knowledge regarding numerous stressor interactions and effects, and that the available evidence is inconclusive on whether synergistic effects are widespread in coral reef systems.
Chapter 3 addresses research objective 2 by using data from the AIMS Long-term Monitoring Program (LTMP) to examine the spatial and temporal overlap of bleaching and disease in the GBR. Coral bleaching and disease have often been hypothesized to be mutually reinforcing or co-occurring, but much of the research supporting this has only drawn an implicit connection through common environmental predictors. I examine whether an explicit relationship between white syndrome and bleaching exists using assemblage-level monitoring data from up to 112 sites on the reef slopes spread throughout the GBR over 11 years of monitoring. None of the temperature metrics commonly used to predict mass bleaching performed strongly when applied to these data, and the inclusion of bleaching as a predictor did not improve model in predicting white syndrome outbreaks. Conversely, the inclusion of white syndrome as a predictor did not improve models of bleaching. Evidence for spatial co-occurrence of bleaching and white syndrome at the assemblage level in this dataset was also very weak. These results suggest the hypothesized relationship between bleaching and disease events may be weaker than previously thought, and more likely to be driven by common responses to environmental stressors, rather than directly facilitating one another.
Chapter 4 addresses research objective 3 by exploring the use of Bayesian Belief Networks (hereafter BBNs) in conjunction with expert elicitation to determine the degree of expert consensus about the greatest threats to the GBR, and assessing the degree of confidence that experts have about the effects of various stressors both alone and in combination. BBNs are finding increasing application in adaptive ecosystem management where data are limited and uncertainty is high. I used a formal expert-elicitation process to obtain estimates of outcomes associated with a variety of scenarios in the GBR that combined stressors both within and outside the control of local managers. Among consulted experts, there was much stronger consensus about certain stressor effects - such as between temperature anomalies and bleaching – than others, such as the relationship between water quality and coral health. In general, models generated from the mean responses from experts predicted that climate change effects could potentially overshadow the mitigating effects of management actions to reduce local stressors.
Chapter 5 addresses research objective 4 by implementing the model developed in Chapter 4 in a spatial way through the use of several scenarios. Coral reefs are one example of an ecosystem where management of local stressors may be a way of mitigating or delaying the effects of climate change. In this chapter, I use a combination of an expert-elicited BBN and empirical, spatial environmental data to examine how hypothetical scenarios of climate change and local management would result in different outcomes for coral reefs on the GBR. I also assess whether reefs within the existing protected area network differ in their predicted probability of decline from reefs outside the protected area network. Parameterizing the BBN using the mean responses from my expert pool resulted in predictions of limited efficacy of local management in combating the effects of climate change; however, there was considerable variability in expert responses; thus, I also examine the effect that using optimistic versus pessimistic expert responses has on the model predictions of coral cover decline on the GBR. Many reefs within the central GBR appear to be at risk of further decline, but further parameterization of the model as data and knowledge become available will improve predictive power. This approach serves as a proof of concept for subsequent work that can fine-tune parameters and explore uncertainties in predictions of responses to management.
My thesis thus addresses two critical elements that are often missing from studies examining the conservation implications of multiple stressors (especially on coral reefs): interactions between stressor/stressor effects and assessing the effect of different management options on these interactions.