Stress-induced rapid release of antibacterials by scleractinian corals

Mechanical stress on the coral Pocillopora damicornis caused the release of material that killed the coral pathogen Vibrio coralliilyticus. The bactericidal material was released into the surrounding seawater rapidly, reaching a maximumkilling activity within 1 min of the stress. The coral antibacterial activity, referred to as CAA, was retained following filter sterilization and storage at - 20 degrees C. Exposure of V. coralliilyticus to CAA for 30 s, 1 min and 6 min resulted in the death of 82%, 89% and 99% of the bacteria, respectively. Release of CAA following mechanical stress was also observed with four other coral species tested. P. damicornis CAA was bactericidal to a wide variety of Gram-negative and Gram-positive bacteria. This is the first report that hard corals rapidly release fast-acting bactericidal material following mechanical stress. The release of CAA was demonstrated with both aquarium corals and corals taken directly from the sea. It is suggested that CAA is part of hard corals' host defense system against infection, the natural stimulation for release of CAAs being the bite of a predator. Previous failures to detect antibacterial activity in hard corals can be attributed to a lack of understanding of the sensitive mechanism by which they are released.