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

Abstract

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 diseaseassociated 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.

Coral Reef Resilience through Biodiversity

“…Bleaching is sometimes, although not always, followed by an outbreak of coral disease involving tissue loss (mortality), and disease outbreaks are not always preceded by bleaching [76,80,[86][87][88]. Diseased corals can be more susceptible to bleaching [77].…”

“…Several recent papers on reef resilience have failed to even mention coral diseases or have not addressed them sufficiently. Coral diseases have caused signi�cant levels of mortality in the Caribbean [87,92,93], and they are of increasing concern in the Indian and Paci�c Oceans (e.g., [76,94,95]). It is possible that in some studies based on insufficiently frequent monitoring at least some coral mortality attributed to bleaching was actually from disease.…”

“…Colonies of all species increased in abundance by 2008. However, in the US Virgin Islands, widespread bleaching in 2005 was followed by a disease outbreak that led to an average decrease in coral cover of c. 60% [87], and little increase in coral cover has been observed In the Caribbean both Acropora palmata and A. cervicornis declined signi�cantly beginning in the late 1970s [13,117,118]. A few studies document some recovery of these species (listed as threatened under the US Endangered Species Act in 2006), but there are currently insufficient data to know if they will ever return to their former abundance and size frequency distributions, (Figure 2).…”

“…Only two were found from the Caribbean (in Belize and St. John, US Virgin Islands). However, the report from St. John [120] was from a reef where coral cover later declined dramatically [87]. Miller et al [87] More research is needed to identify the characteristics of resistant and resilient reefs in the face of all components of global climate change.…”

“…In the US Virgin Islands, aer severe bleaching and disease in 2005/2006, species in the Montastraea annularis complex declined signi�cantly but remained the most abundant. Almost all species were affected, and even the most sensitive (Agaricia agaricites) survived [87]. Côté and Darling [128] seem to assume that species will respond the same way each time they are stressed, for example during a bleaching event.…”