The complexities arise from different levels of symbiosis within a coral, both with bacteria on the surface and algae in the interior. Moreover, the warmer waters cause increased virulence of some pathogens as well as a diminished ability of corals to fight them. But these complications can also be keys to coral reef survival.
"A first line of defense is provided by surface microorganisms [that] produce antibiotics that can help corals fight pathogenic bacteria," reported Harvell.
However, not all corals are able to produce such defenses under thermal stress. "Some corals show unusual resilience to the double threat [of pathogens and warming seas], and we should look to these hardy corals for clues that might enhance others," said Harvell. "Other corals are more sensitive and will not survive the continued warming trend."
Yet there seems to be future promise for boosting the immunity of coral reefs, Harvell reported. Collaborators Rotem Effrony and Eugene Rosenberg in Tel Aviv, Israel, have isolated viruses that can consume several bacteria that are deadly to the more sensitive corals.