https://phys.org/news/2018-11-corals-molecules-resist-disease.html

Using water samples from 18 coral colonies along the Abu Dhabi coast, each of which was sampled at different distances from the coral surface, the study's researchers have discovered that Acropora and Platygyra corals harbor unique bacteria and molecules at their surface, distinctly different from surrounding seawater. These molecules were identified as chemo-attractants, antibacterials, or signaling molecules, suggesting they may structure coral surface-associated microbes. Their findings show that there is a distinct gradient of molecules surrounding corals, and that these molecules may help recruit beneficial bacteria and/or defend against parasitic bacteria.

Furthermore, the researchers have detected surface associated molecules characteristic of healthy or white-syndrome disease infected corals, a finding which may aid in predicting the onset of disease.