No description available.

Thesis (M.S.)--University of Hawaii at Manoa, 2007. / Includes bibliographical references. / viii, 75 leaves, bound ill. 29 cm

Thesis (Ph. D.)--University of Technology Sydney, 2008.

Coral ecosystems are highly diverse and productive ecosystems in tropical and subtropical oceans, playing a significant role in marine ecosystems. They have many important functions: a carbon sink in the global carbon cycle via calcification, habitats for many economically important species, acting as shoreline buffers, and a potential source of natural chemical substances of medical importance (Moberg et al. 1999). Growth and erosion are the two driving forces that determine the fate of a coral reef. Coral growth is achieved by calcification - the deposition of calcium carbonate skeleton by living coral polyps, and erosion refers to the removal of calcium carbonate by physical or biological factors. When calcification exceeds erosion, a reef is considered to be growing and vice versa. Hence, the study of this growth-erosion balance is the key to evaluating the health status of a reef. Hong Kong, as a marginal environment for coral survival has a remarkable diversity of coral communities in its waters. However, little is known about the calcium carbonate budget of these communities. My study thus aims to fill in this gap of knowledge in order to better understand and conserve these valuable communities. This study is timely given that many global and regional stressors are expected to affect coral calcium budget. The results of my study can contribute to a better understanding of how corals respond to environmental changes. This study aims to 1) explore any correlation between environmental factors and abundance of internal borers on corals; 2) study the growth rate of corals across different environmental gradients in Hong Kong; and 3) study the rate of erosion of corals across different environmental gradients across nine sites in Hong Kong. Field surveys were carried out at 33 sites from October 2012 to December 2012 covering two environmental gradients - from estuarine to oceanic and from sheltered to exposed. Two 50-meter transects were laid at each site and coral coverage and abundance of eroders per colony was determined using photo quadrants. Three sediment traps were also deployed at each site and collected after a month to determine sedimentation and nutrition deposition rate. Correlation analyses were conducted to explore any underlying relationships between borehole densities on corals and environmental factors. It was found that polychaete boreholes were significantly positively related to the amount of sedimentation. Also, the bioerosion of corals in Hong Kong was found out to be much more serious than that in other regions. From the 33 sites surveyed to determine borehole densities, 10 sites chosen to cover two environmental gradients were selected for more detailed studies of coral growth. Three colonies of Porties lutea of around 20 cm x 20 cm x 20 cm were collected from each site, and were cut into 1cm slabs parallel to the direction of maximum growth. X-ray radiography was done for each slab to analyze the growth rate. The growth of Porties lutea across the 10 sites were compared against other regions and underlying relationships with environmental factors were explored. It was found that the growth of corals was negatively correlated with sedimentation rate, and the calcification rates of corals in Hong Kong were much lower than those reported from many study conducted in tropical regions. To understand the rate of bioerosion of corals in Hong Kong, a study was conducted by deploying experimental coral skeleton blocks at nine chosen sites. Three blocks were deployed at each site. Blocks were retrieved after one year and scanned with MicroCT to examine the contribution on internal bioerosion by different taxa as well as the total amount of bioerosion at each site. The data were analyzed to understand internal how bioerosion is determined by environmental factors. It was found that bioerosion contributed by polychaetes had positive correlation with the sedimentation rate, which was consistent with the results found in the forth-mentioned study of coral slabs. The internal bioerosion rates of corals in Hong Kong were within the range of the corresponding data reported from overseas.

No description available.

No description available.

University of Technology, Sydney. Faculty of Science. / Global climate change is leading to the rise of ocean temperatures and is triggering mass coral bleaching events on reefs around the world. This involves the expulsion of the symbiotic dinoflagellate algae, known as zooxanthellae, from the coral host. Coral bleaching is believed to occur as a result of damage to the photosynthetic apparatus of these symbionts, although the specific site of initial impact is yet to be conclusively resolved. This thesis examined a number of sites within the light reactions of photosynthesis and evaluated the efficiency of photoprotective heat dissipating pathways. Upon expulsion, the capacity for long-term survivorship of expelled zooxanthellae in the water column was also assessed. A reduction in photosystem II (PSII) photochemical efficiency during exposure to elevated temperature and high light (bleaching conditions) was found to be highly dependent upon the increase in abundance of QB non-reducing PSII centres (inactive PSII centres), indicating damage to the site of the secondary electron acceptor, QB, resulting in a limited capacity for its reduction. Therefore, this reduced the rate of the reoxidation of the primary electron acceptor, QA-. Fast induction curve (FIC) analysis of the rise from minimum fluorescence to maximum fluorescence revealed a lower amplitude in the J step along this curve, which was consistent with a reduction in the rate of QA reoxidation. This photoinhibition of PSII was found to occur once the effectiveness of excess energy dissipation through energy-dependent quenching and state-transition quenching was exceeded, suggesting that these mechanisms were incapable of preventing photodamage. Antenna size heterogeneity showed little change under bleaching conditions with a significant increase in PSIIbeta only apparent in one species of coral. The thermostability of the oxygen evolving complex (OEC) and thylakoid membrane were found to increase during exposure to bleaching conditions and exceeded bleaching thresholds of corals. This rapid rise in temperature-dependent thermostability also occurred over seasons, where variation in ocean temperatures was matched by gradual shifts in OEC and thylakoid membrane thermotolerance. Variation in thermostability between species was not found to be linked to zooxanthellae genotype, and instead was related to the bleaching susceptibility of the host. Despite this capacity for resilience to bleaching conditions, the PSII reaction centres did not exhibit such a mechanism for rapid acclimatisation. Corals can only be as tolerant to bleaching conditions as their most sensitive component allows. The formation of nonfunctional PSII centres is therefore suggested to be involved in the initial photochemical damage to zooxanthellae which leads to a bleaching response. Zooxanthellae were found to be expelled irrespective of OEC function and thylakoid membrane integrity, as these sites of the photosynthetic apparatus were still intact when cells were collected from the water column. Although zooxanthellae were photosynthetically competent and morphologically intact upon expulsion, their longevity in the water column was dependent on the time of expulsion following the onset of bleaching and the ambient water temperatures. The survivorship of these zooxanthellae was restricted to a maximum of 5 days in the water column which suggests that unless expelled zooxanthellae inhabit other environs of coral reefs which may be more favourable for survival, their capacity for persistence in the environment is extremely limited. Chlorophyll a fluorescence measurements are a common tool for investigating photosynthetic impacts to in hospite zooxanthellae of corals. Pathways causing dark-reduction of the plastoquinone pool are shown to be active in corals and affect measurements which require dark-adaptation. Pre-exposure to far-red light was found to be an effective procedure to oxidise the inter-system electron transport chain and ensure determination of the true maximum quantum yield of PSII and accurate FICs. It is concluded that the trigger for coral bleaching lies in the photosynthetic apparatus of zooxanthellae and evidence is presented in support of this impact site not being the OEC or thylakoid membrane.

none

Thesis (M.S.)--University of Hawaii at Manoa, 2003. / Includes bibliographical references (leaves 49-58). Also available via World Wide Web.

University of Technology, Sydney. Faculty of Science. / Global climate change is leading to the rise of ocean temperatures and is triggering mass coral bleaching events on reefs around the world. This involves the expulsion of the symbiotic dinoflagellate algae, known as zooxanthellae, from the coral host. Coral bleaching is believed to occur as a result of damage to the photosynthetic apparatus of these symbionts, although the specific site of initial impact is yet to be conclusively resolved. This thesis examined a number of sites within the light reactions of photosynthesis and evaluated the efficiency of photoprotective heat dissipating pathways. Upon expulsion, the capacity for long-term survivorship of expelled zooxanthellae in the water column was also assessed. A reduction in photosystem II (PSII) photochemical efficiency during exposure to elevated temperature and high light (bleaching conditions) was found to be highly dependent upon the increase in abundance of QB non-reducing PSII centres (inactive PSII centres), indicating damage to the site of the secondary electron acceptor, QB, resulting in a limited capacity for its reduction. Therefore, this reduced the rate of the reoxidation of the primary electron acceptor, QA-. Fast induction curve (FIC) analysis of the rise from minimum fluorescence to maximum fluorescence revealed a lower amplitude in the J step along this curve, which was consistent with a reduction in the rate of QA reoxidation. This photoinhibition of PSII was found to occur once the effectiveness of excess energy dissipation through energy-dependent quenching and state-transition quenching was exceeded, suggesting that these mechanisms were incapable of preventing photodamage. Antenna size heterogeneity showed little change under bleaching conditions with a significant increase in PSIIbeta only apparent in one species of coral. The thermostability of the oxygen evolving complex (OEC) and thylakoid membrane were found to increase during exposure to bleaching conditions and exceeded bleaching thresholds of corals. This rapid rise in temperature-dependent thermostability also occurred over seasons, where variation in ocean temperatures was matched by gradual shifts in OEC and thylakoid membrane thermotolerance. Variation in thermostability between species was not found to be linked to zooxanthellae genotype, and instead was related to the bleaching susceptibility of the host. Despite this capacity for resilience to bleaching conditions, the PSII reaction centres did not exhibit such a mechanism for rapid acclimatisation. Corals can only be as tolerant to bleaching conditions as their most sensitive component allows. The formation of nonfunctional PSII centres is therefore suggested to be involved in the initial photochemical damage to zooxanthellae which leads to a bleaching response. Zooxanthellae were found to be expelled irrespective of OEC function and thylakoid membrane integrity, as these sites of the photosynthetic apparatus were still intact when cells were collected from the water column. Although zooxanthellae were photosynthetically competent and morphologically intact upon expulsion, their longevity in the water column was dependent on the time of expulsion following the onset of bleaching and the ambient water temperatures. The survivorship of these zooxanthellae was restricted to a maximum of 5 days in the water column which suggests that unless expelled zooxanthellae inhabit other environs of coral reefs which may be more favourable for survival, their capacity for persistence in the environment is extremely limited. Chlorophyll a fluorescence measurements are a common tool for investigating photosynthetic impacts to in hospite zooxanthellae of corals. Pathways causing dark-reduction of the plastoquinone pool are shown to be active in corals and affect measurements which require dark-adaptation. Pre-exposure to far-red light was found to be an effective procedure to oxidise the inter-system electron transport chain and ensure determination of the true maximum quantum yield of PSII and accurate FICs. It is concluded that the trigger for coral bleaching lies in the photosynthetic apparatus of zooxanthellae and evidence is presented in support of this impact site not being the OEC or thylakoid membrane.