Resource managers must address three critical questions when disease is detected in management areas:
- How widespread is the disease?
Criteria that should be considered when deciding which areas to survey for extent of disease include, but are not limited to, percent coral cover, species richness, proximity to the original site of disease detection, susceptibility of the population, and accessibility of the site. When assessing the geographic extent of disease, managers should address the following questions:
Does the disease primarily affect a particular group or genus of corals?
Does the disease primarily affect a particular size class of coral?
Does the disease appear to be spreading between adjacent colonies?
Do corals affected by the disease have a particular spatial distribution?
Have there been recent changes in the environment?
Does disease occur more frequently during certain times of the year?
- Is the disease spreading and if so, how fast?
Visual surveys of geographic extent over time can give an indication of how fast a disease is spreading.
- Is the disease killing animals?
This is measured as the percent of colonies having a disease that actually die from that disease. Managers should be more concerned with diseases that have a high case fatality rate.
To answer these questions, the state of disease in the ecosystem must be monitored over time. Deciding how frequently to monitor is dictated primarily by the behavior of the disease in the field. For example, diseases that appear to be spreading rapidly will need more frequent monitoring than those that are spreading slowly or appear static. It is important during this phase of monitoring to liaise with appropriate experts who can help determine the cause of disease. The Coral Disease Handbook (see Resources, below) provides guidance in developing a monitoring program to address the impacts of disease on coral communities.