Coral Disease

Coral disease

Coral diseases were first reported on reefs in the Florida Keys and Caribbean in the 1970s. In the decades since, they have been reported worldwide and with increasing frequency. Disease is now recognized as one of the major causes of reef degradation and coral mortality. Recent research has suggested that coral diseases may be secondary opportunistic infections, rather than the result of primary pathogens, making it imperative to understand the microbial shifts that accompany the transition from healthy to diseased corals. Additionally, we need to determine if the spread of coral disease is affected by the level of connectivity among water masses, organisms, trophic levels, or habitats. See black-band disease and coral bleaching galleries below.

We investigated coral disease processes and causes by characterizing microbial communities in diseased and healthy representatives of selected coral species both temporally and spatially by employing microarray technology. We tested the diagnostic potential of coral fluorescence for identifying disease-induced physiological stress. This work links coral ecosystem studies in marine protected areas to better understand coral ecosystem health.

Specific research efforts included:

• Comparing microbial communities between diseased and healthy corals from two species in two National Parks: Dry Tortugas National Park and Virgin Islands National Park.

• Utilizing microarray technology (representing 30,000 microbial taxa) to get a taxonomic overview of the shifts in microbial communities between healthy and diseased corals, between species of corals, and between different geographic areas

• Comparison of DNA preservation methods for environmental bacterial community samples.

  Field collections of environmental samples, for example corals, for molecular microbial analyses present distinct challenges. The lack of laboratory facilities in remote locations is common, and preservation of microbial community DNA for later study is critical. A particular challenge is keeping samples frozen in transit.

  Five preservation methods that do not require cold storage were compared for effectiveness over time and ease of use. Mixed microbial communities of known composition were created and preserved by DNAgard™, RNAlater®, DMSO–EDTA–salt (DESS), FTA® cards, and FTA Elute® cards. Microbial community fingerprinting analysis and DNA sequencing were used to detect specific changes in the known communities over weeks and months of storage. A previously known bias in FTA® cards that results in lower recovery of pure cultures of Gram-positive bacteria was also detected in mixed community samples. There appears to be a uniform bias across all five preservation methods against microorganisms with high G + C DNA. Overall, the liquid-based preservatives (DNAgard™, RNAlater®, and DESS) outperformed the card-based methods. No single liquid method clearly outperformed the others, leaving method choice to be based on experimental design, field facilities, shipping constraints, and allowable cost.

• Field testing a new technique to determine if coral fluorescence can be used to remotely assess coral health

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