In the last 30 years, more than 90 percent of the reef-building coral in the Caribbean has disappeared because of a disease of unknown origin.

Now, scientists from the University of Florida have used a GIS (geographic information system) to show the whereabouts of the clusters of diseased coral. Their findings, published in the journal PLoS One, may help researchers derive better hypotheses to determine what contributes to coral disintegration.

Microbiologists and toxicologists often run laboratory tests on small samples of Acropora species of coral to determine the factors that contribute to white-band disease, known as WBD. It’s visually identified as a white band moving from the base of the coral up, killing the coral tissue as it goes, leaving only the exposed coral skeleton behind.

Laboratory results spur a range of theories of causation — anything from opportunistic pathogens to specific bacterial infections. Other scientists suggest that WBD is not the result of an outside agent, such as bacteria, but rather a stress response from the coral in reaction to changes in the marine environment, such as ocean pollution and rising ocean temperatures due to climate change.

This study searches for patterns in the incidence of the disease.

The researchers found the locations of significant disease clusters, information scientists can then use to narrow where they should take samples for further laboratory tests. This is the first of several studies established by the researchers exploring which types of spatial analysis are the most appropriate for various types of coral data from the Caribbean.

For thousands of years, Acropora was the predominant coral in the Caribbean, but more than three decades of disease have destroyed the species ability to survive, forcing marine life out of their coral habitats, which exposes them to attack by predators.

Acropora corals are distinctive – no other corals resemble their complex branching structure, which provides ideal habitat for many coral reef organisms. In terms of size, Acropora corals range from a dinner plate to a family car. Acropora species appear to be among the fastest growning corals, with upwward growth between 10 and 20 cm per year. Acropora is usually branched, except when young, but the size and shape of the branches vay according to the species concerned.

GIS systems are increasingly being used to assess coral reefs.

Further reading:
Lentz JA, Blackburn JK, Curtis AJ, 2011 Evaluating Patterns of a White-Band Disease (WBD) Outbreak in Acropora palmata Using Spatial Analysis: A Comparison of Transect and Colony Clustering. PLoS ONE 6(7): e21830. doi:10.1371/journal.pone.0021830
Geographical Information Systems
A low-cost procedure for automatic seafloor mapping, with particular reference to coral reef conservation in developing nations, Trond-Inge Kvernevik, Mohd Zambri Mohd Akhir and Jill Studholme