Abstract:
The increasing number and geographic spread of coral diseases over the past three
decades is threatening the diversity and viability of coral reef ecosystems. Little is known
about the causes of disease outbreaks in coral; how coral diseases are transmitted; or the
relative impact of climate, environmental stressors, and anthropogenic factors on coral
disease, making the prevention and/or mitigation of coral disease impacts difficult if not
impossible. The coral disease white plague type II (WPII) is a particularly virulent and
fast moving disease, affecting 38 documented species of Caribbean scleractinian corals.
WPII has the ability to destroy coral tissue at a rate of up to 10 cm/day, with the ability to
kill entire colonies within days. Loss of tissue from the margin of several coral species at
the Flower Garden Banks National Marine Sanctuary in the Gulf of Mexico in May 2005
suggested that the corals were affected by WPII. The goals of this study were to
enumerate the microbial communities associated with suspect WPII coral disease, to
compare the microbial abundance and community composition (diversity) between the
healthy and diseased coral tissue, and to verify whether a previously proposed etiological
agent of WPII, the bacterium Aurantimonas coralicida, was present in the diseased coral
tissue. Triplicate coral core samples were collected from suspect WPII diseased-margin
tissue, apparently healthy tissue on diseased coral colonies, and healthy tissue from four
paired coral colonies from the Flower Garden Banks National Marine Sanctuary in the
Gulf of Mexico. The culturable microbial communities were enumerated and then
examined by molecular fingerprinting and 16S rRNA gene sequencing. The bacterial
abundance data suggest that variations may be due, in part, to coral species-specific and
site-specific factors. The length heterogeneity polymerase chain reaction (LH-PCR)
fingerprinting and 16S rRNA gene sequencing data suggest that for selected bacterial
colonies there was a relatively high degree of similarity among the culturable bacterial
populations associated with apparently healthy tissue on diseased coral, healthy coral
tissue, and diseased-margin coral tissue. Much of the variability in the presence of these
bacterial populations was found in the less abundant taxa. The bacterium A. coralicida
was not detected using LH-PCR to characterize the culturable bacterial colonies, even
though isolates were selected based on morphological characteristics of A. coralicida to
focus on likely candidates.
