| Coral reefs worldwide are in the midst of historically unprecedented changes. Episodes of algal blooms, mass coral bleaching, disease outbreaks and shifts in the dominance of benthic organisms all appear to have begun in the 1970s and to have increased in frequency, intensity, variety and range over the past two decades. Are these changes simply coincidental, or might they be linked by a common factor? On the basis of well-documented observations relating to climate and atmospheric aerosols, and the widely accepted increases in the rate at which coral diseases are appearing worldwide, this dissertation considers whether variability in the supply of iron-rich eolian (wind-blown) dust to typically iron-poor marine environments may alter the micronutrient factors limiting the growth of opportunistic organisms and the virulence of pathogenic microbes.; The intellectual approach to this question ranges from satellite oceanography to molecular microbiology. Analyses of satellite-derived data from the tropical Atlantic Ocean suggest that while satellites provide a powerful means to measure bulk properties of the oceans and atmosphere, the resulting information is less helpful at resolving the relationship between environmental iron (Fe) variability and episodic changes in phytoplankton biomass. Experimentation with a confirmed bacterial pathogen of stony corals, Aurantimonas coralicida, and a temperate stony coral, Oculina arbuscula , enables more focused examination of a hypothesized functional link between Fe and biology. Using experimental microcosms and mesocosms, this research demonstrates that reagent Fe and environmental Fe derived from African sediments affect bacterial growth in vitro and alter the commensal bacterial community on the surface of O. arbuscula in vivo . Bioassays confirm that A. coralicida is able to synthesize strong Fe-binding ligands and may also possess machinery to access exogenous Fe-binding ligands present in the environment. These results confirm that process-level investigation represents the most effective, initial approach toward a better understanding of how environmental Fe affects coral reef biology. |
