Relationships between the history of thermal stress and the relative risk of diseases of Caribbean corals.

The putative increase in coral diseases in the Caribbean has led to extensive declines in coral populations. Coral diseases are a consequence of the complex interactions among the coral hosts, the pathogens, and the environment. Yet, the relative influence that each of these components has on the prevalence of coral diseases is unclear. Also unknown is the extent to which historical thermal-stress events have influenced the prevalence of contemporary coral diseases and the potential adjustment of coral populations to thermal stress. We used a Bayesian approach to test the hypothesis that in 2012 the relative risk of four signs of coral disease (white signs, dark spots, black bands, and yellow signs) differed at reef locations with different thermal histories. We undertook an extensive spatial study of coral diseases at four locations in the Caribbean region (10(3) km), two with and two without a history of frequent thermal anomalies (approximately 4-6 years) over the last 143 years (1870-2012). Locations that historically experienced frequent thermal anomalies had a significantly higher risk of corals displaying white signs, and had a lower risk of corals displaying dark spots, than locations that did not historically experience frequent thermal anomalies. By contrast, there was no relationship between the history of thermal stress and the relative risk of corals displaying black bands and yellow signs, at least at the spatial scale of our observations.

Caribbean yellow-band syndrome on Montastraea faveolata is not transmitted mechanically under field conditions.

Caribbean yellow-band syndrome is a highly prevalent coral disease whose transmission mechanisms are unknown. Affected corals often show multifocal lesions of yellow-colored tissue. We tested the hypothesis that a mechanical vector was responsible for these multifocal lesions. Four presumably non-resistant colonies were experimentally manipulated. Tissue and microbial assemblages were taken from diseased tissue and injected into healthy-looking tissue. Seawater injections were used as controls. The manipulations created a small wound, as would be generated by a coral predator. After 1 mo, all lesions healed and showed no signs of disease. We therefore reject the hypothesis that a mechanical vector, acting in a similar way as our manipulations, was responsible for the multifocal lesions.