HR: 10:55h
AN: B11F-03    [PDF]
TI: Establishing a Functional Link Between African Dust and Region-wide Coral Reef Decline
AU: * Hayes, M L
EM: mhayes@centrescientifique.mc
AF: Centre Scientifique de Monaco, Av Saint Martin, Monte Carlo, 98000 Monaco
AU: Barber, R T
EM: rbarber@duke.edu
AF: Duke University Nicholas School of the Environment and Earth Sciences, 135 Duke Marine Lab Rd., Beaufort, NC 28516 United States
AB: For nearly thirty years, coral reefs in the Western Atlantic and Caribbean basin have experienced historically unprecedented declines. Algal blooms, mass coral bleaching, disease outbreaks and shifts in the dominance of benthic coral-competitors were first documented in the 1970s and have increased in frequency, intensity, variety and range over the past two decades. Recent studies of decreasing coral cover document regional losses averaging nearly 80% over this period. Here, we provide experimental evidence that increased supplies of iron-rich eolian dust from Africa to typically iron-poor marine environments throughout the region could have played a key role in these profound changes. Atmospheric inputs of "new" micronutrients, especially iron, have the potential to overcome limitations to the growth of opportunistic coral-competitors and the virulence of coral pathogens. Microcosm and mesocosm experiments with a putative bacterial pathogen of stony corals, {\it Aurantimonas coralicida}, and a temperate stony coral, {\it Oculina arbuscula}, provide a means to test the functional relationship between iron availability, microbial growth and coral health. Iron limitation of A. coralicida growth rates is readily induced by the addition of synthetic chelators such as 2,2' Dipyridyl to bacterial cultures at relatively low concentrations (e.g. 10 $\mu$M). This growth limitation is reversed by 100 nM over-enrichments of pure reagent-grade iron as well as iron-rich "synthetic dust" derived from African lake-bed sediments. The Chrome-azurol S assay demonstrates that A. coralicida also synthesizes high-affinity iron-capture mechanisms (i.e. siderophores) that may serve as critical determinants of virulence. Finally, our experimental mesocosms are based on oligotrophic Mediterranean seawater and permit controlled experimentation under relatively low iron ($\sim$5 nM) conditions. Using this system, denaturing gradient gel electrophoresis (DGGE) analysis of PCR-amplified ribosomal DNA fragments is used to study changes in the bacterial community associated with corals incubated under Fe-replete and Fe-deplete conditions. Observations of marked variability in coral bacterial profiles suggest that certain bacterial species on coral surfaces are responsive to shifts in environmental iron levels. These experiments begin to provide a mechanistic understanding of how dust, and in particular, environmental iron, might affect survival and competition in the coral reef community. This novel, model-based experimental approach can be further extended to virulence bioassays and may be useful for other process studies of coral-microbe interactions as well.
DE: 4800 OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL
DE: 4840 Microbiology
DE: 4875 Trace elements
DE: 9325 Atlantic Ocean
SC: Biogeosciences [B]
MN: 2003 Fall Meeting