E. Muller | USGS Science

USGS2009

Coral disease following massive bleaching in 2005 causes 60% decline in coral cover on reefs in the US Virgin Islands

In the northeast Caribbean, doldrum-like conditions combined with elevated water temperatures in the summer/fall 2005 created the most severe coral bleaching event ever documented within this region. Video monitoring of 100 randomly chosen, permanent transects at five study sites in the US Virgin Islands revealed over 90% of the scleractinian coral cover showed signs of thermal stress by paling or becoming completely white. Lower water temperatures in October allowed some re-coloring of corals; however, a subsequent unprecedented regional outbreak of coral disease affected all sites. Five known diseases or syndromes were recorded; however, most lesions showed signs similar to white plague. Nineteen scleractinian species were affected by disease, with >90% of the disease-induced lesions occurring on the genus Montastraea. The disease outbreak peaked several months after the onset of bleaching at all sites but did not occur at the same time. The mean number of disease-induced lesions increased 51-fold and the mean area of disease-associated mortality increased 13-fold when compared with pre-bleaching disease levels. In the 12 months following the onset of bleaching, coral cover declined at all sites (average loss: 51.5%, range: 42.4-61.8%) reducing the five-site average from 21.4% before bleaching to 10.3% with most mortality caused by white plague disease, not bleaching. Continued losses through October 2007 reduced the average coral cover of the five sites to 8.3% (average 2-year loss: 61.1%, range: 53.0-79.3%). Mean cover by M. annularis (complex) decreased 51%, Colpophyllia natans 78% and Agaricia agaricites 87%. Isolated disease outbreaks have been documented before in the Virgin Islands, but never as widespread or devastating as the one that occurred after the 2005 Caribbean coral-bleaching event. This study provides insight into the effects of continued seawater warming and subsequent coral bleaching events in the Caribbean and highlights the need to understand links between coral bleaching and disease. ?? The Author(s) 2009.

Coral Reefs↗

USGS2009

Extensive coral mortality in the US Virgin Islands in 2005/2006: A review of the evidence for synergy among thermal stress, coral bleaching and disease

In the summer/fall of 2005, extensive coral bleaching on reefs in the US Virgin Islands (USVI) was associated with sea water temperatures exceeding 30°C. Almost all coral species bleached, including Acropora palmata , which bleached for the first time on record in the USVI. As water temperatures cooled, corals began to regain their normal coloration. However, a severe disease outbreak then occurred on deeper, non-acroporid reefs. The disease demonstrated signs consistent with white plague. Monitoring of coral cover along previously established long-term transects on several reefs in St. John and St. Croix was intensified. Data on bleaching and disease were collected before, during and after this bleaching/disease episode. Average coral cover declined by over 50%, from 21.4% to 10.3% at the long-term study sites, within one year of the onset of bleaching, declining further to 8.3% after two years. This loss of coral cover was greater than from all other stressors affecting the USVI reefs in preceding years, and no significant recovery is evident. Disease prevalence increased on bleached A. palmata colonies that were being monitored as well as on the colonies of other species on the deeper reefs. Bleached A. palmata colonies had more disease (primarily white pox and other un-described diseases) than unbleached colonies. The non-acroporid corals that bleached most severely suffered the highest mortality from disease. Although the research summarized in this paper is not conclusive, the results suggest that high water temperatures lead to bleaching, which weakens corals and makes them more vulnerable to diseases.

U.S. Virgin Islands↗