The coral disease Stony Coral Tissue Loss Disease (SCTLD), caused by previously unknown pathogens, has been affecting the coral reefs off the coast of Florida and in the Gulf of Mexico since 2014. It eats away the coral tissue down to the white calcium carbonate skeleton. Researchers led by Valerie Paul of the Smithsonian Institution’s Marine Research Station in Florida have discovered the first effective bacterial probiotic to treat and prevent the mysterious disease SCTLD.
Coral death due to ocean acidification, rising sea temperatures and physical destruction is on everyone’s lips. It is mainly triggered by coral bleaching. The corals eject their algae symbionts when the water is too warm or too polluted. While this process and its triggers are now well understood, the emerging coral disease SCTLD is not. So far it is unclear what causes this spreading disease, but it is suspected that a bacterial pathogen is behind it.
While examining SCTLC-infested reefs off the Florida coast, Paul and her team noticed that in some places the corals are spared from SCTLD as the disease spreads to the surrounding area. The researchers therefore collected samples of 222 strains of bacteria found in the healthy areas to find out whether these microbes might protect the corals from the pathogens.
After experimental, chemical and genetic tests, it was established that some of the microorganisms detected on the healthy corals, particularly McH1-7, protect the large corals from SCTLD through their antimicrobial activity. The probiotic obtained from these bacteria can now be used in the future as an alternative to the broad-spectrum antibiotic amoxicillin. Not only is it more effective at fighting SCTLD, but it also reduces the risk of spreading antibiotic-resistant bacteria through broad-spectrum treatment, the team explains. A prophylactic treatment was not previously possible, but now the probiotic can be introduced into the coral and become a protective part of the ecosystem in the long term.
Whether McH1-7 is effective in all of the approximately two dozen affected species and in all reefs in the 20 affected countries remains to be determined. The first field trials on the Florida coast should answer these questions.