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Title: Understanding the nature and significance of fluorescence in massive corals of the species Porites lutea from Phuket, Thailand
Author: Theodoran, N. K.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1995
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Bright bands in massive corals of the species Porites lutea have been associated with periods of increased rainfall. However, stain experiments involving Porites lutea from Mo Phuket have shown that bright bands are deposited during the dry season. Thus, one of the main objectives of this thesis was to understand more fully the processes that are involved in the production of fluorescent bands. The second major objective was to build a device that could reliably record fluorescent emissions directly from solid coral. It was hoped that the fluorescent emissions recorded in this way could then be compared with environmental factors, and in particular rainfall. In order to achieve the first objective, solid state coral fluorescence was examined to determine (1) what effects porosity (macro and micro) have on coral fluorescence, and (2) the distribution of fluorophores in the skeleton. By studying the fluorescence of solutions in which the CaCO3 has been removed by acid dissolution, it was possible to determine the effects of both fluorophore concentration and the metal ions, iron and manganese, on coral fluorescence. Environmental samples (soil, sediment, seawater and polyp tissue) were also examined in an attempt to identify the source(s) of coral fluorophores. Although Boto and Isdale (1985) have suggested that terrestrial humic acid is responsible for bright band fluorescence in Porites lutea, the same, or very similar, fluorophores were found in both bright and dull bands. Two main types of fluorophore were identified, a 330-340 nm excitation peak group and a 390 nm excitation peak group. Work has shown that changes in the absolute concentration of these fluorophores (i.e. their relative concentrations remain constant) appears to be the main control on fluorescent banding. Increases in fluorophores concentration can result in both a change in the colour of coral fluorescence as well as a change in intensity. When solid coral was viewed using a fluorescence microscope, two main types of fluorescence were seen, yellow/orange fluorescent patches and a blue background fluorescence. The yellow/orange fluorescent patches were randomly distributed, ranged in size from 8-35 μm and appeared to be due to black, possibly organic, inclusions (sub-micron to 3 μm). Although the distribution of these patches was not mapped, observations suggested that they were more numerous in bright bands. This thesis suggests that differences in the ratio of yellow/orange fluorescent patches to background fluorescence controls the colour of coral fluorescence. As fluorescent emissions in the solid state are dominated by short wavelength emissions, the background region of the coral (which is also dominated by short wavelength emissions) is thought to exert the main control on fluorescent intensity. Although terrestrial surface soil contained the most concentrated source of coral-like fluorophores, it was not possible to confirm the origin of coral fluorescence as coral-like fluorophores were found in all the environmental samples.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available