Coral disease assessments and monitoring should seek to answer specific questions about the area, including the following:
- Are coral disease(s) present? If so, which ones?
- Is the disease spreading, and if so, how fast?
- What species are affected? Does the disease primarily affect a particular size class or morphology of coral?
- How severe are the impacts caused by the disease? Are corals dying?
- Are there reefs, reef zones or reef areas that are more affected than others?
- Have recent changes in the environment been observed that may encourage coral diseases to spread?
Some diseases only cause reduced growth rather than mortality (e.g., Porites trematodiasis), whereas others can cause significant mortality (e.g., tissue loss diseases such as white syndromes). Managers should be most concerned with diseases that cause a high mortality rate.
Standardized approaches to investigate coral disease have recently been developed.ref Initial steps to assess coral disease include documenting the spatial extent of the disease outbreak, and investigating whether the outbreak could have resulted from a recent environmental perturbation, such as anomalous changes in water temperature, sewage spills, or chemical contaminants. ref Based on these results, an action plan can be developed to determine which variables should be measured and which methodologies should be used. Decisions will take into account the type and severity of the event, location of the event and available resources.
If resources are available, managers may implement detailed disease assessments. Such assessments may include quantification of susceptible species, prevalence (proportion of corals affected), and a description of lesions on affected corals. ref Microbiologic, molecular and histological analyses of disease processes may also be conducted, requiring the collection of coral and environmental samples. Disease monitoring efforts will usually benefit from taking photographic records to enable consultation with disease experts.
There is no one correct method for assessing coral disease. A suite of field methods are available and managers will need to determine the most appropriate method for their site(s). For an explanation of commonly used methods to assess coral disease, see the Coral Disease Handbook and Hawaii’s Rapid Response Contingency Plan in Resources, below.