Impact of a coral disease outbreak on coral communities in St. Lucia: What and how much has been lost?

In July 1997, a coral disease called plague appeared on the coral reefs of St. Lucia, West Indies. A survey of 6 coral species on 3 reefs in March 1998 revealed an overall disease incidence of 11%. Montastraea faveolata and Colpophyllia natans were the most affected species with 19% and 13% of colonies infected respectively. Disease frequency was independent of coral density and the distribution of the disease among 5 x 5 m plots was not clumped, suggesting that proximity to affected colonies did not increase probability of infection. Among-colony size variation in disease incidence and tissue mortality indicates that small coral colonies are more likely to escape infections than large colonies, but once infection occurs, small colonies will experience faster colony mortality. This suggests that the effect of the disease on coral population structure will be greater total mortality in small colonies relative to large colonies, at least over short-time scales. At the most severely affected site, it was estimated in March 1998 that plague had killed 6.6% of living coral during the preceding 8 months. Despite these losses being small compared to losses from other well-known disturbances on coral reefs, such as hurricanes, the disease selectively impacted 2 major reef frame builders. More than 90% of the estimated tissue loss was accounted for by Montastraea faveolata and Colpophyllia natans combined. In addition, infected colonies continued to lose living tissue from February 1998 to October 1998, with no new coral recruitment observed on the substrate opened up by the disease. Of the colonies infected in February 1998, 28% still showed signs of disease in October 1998, Over the long term, if losses are sustained at such rates, plague could cause complete mortality in large colonies and could progressively deplete two of the most important reef frame builders in some of the richest and most visited coral reefs of St. Lucia.