Natural products from Caribbean octocorals demonstrate bioactivity against Vibrio coralliilyticus strains

Caribbean coral reefs are currently facing a rapid decline caused by a plethora of threats including disease outbreaks. Octocorals appear to be unaffected by the majority of diseases impacting scleractinian corals, including stony coral tissue loss disease (SCTLD) that emerged in 2014 and resulted in a mass mortality of scleractinian coral populations inhabiting Florida, the USA, and Caribbean reefs. Although the Caribbean Sea is considered a disease hot spot, few investigations into the mechanism(s) responsible for the resistance of octocorals have been conducted. In response, the capacity for octocoral-derived extracts and natural products to inhibit strains of Vibrio coralliilyticus, pathogenic bacteria that can cause bleaching and disease in stony corals and can co-occur in SCTLD infections, was explored. Extracts obtained from each of the four octocoral species studied demonstrated antimicrobial activity against V. coralliilyticus. Bioassay-guided fractionations of crude extracts from Antillogorgia americana were employed to identify the antimicrobial compounds, revealing the presence of secosterols in the most bioactive fractions. These results suggest that octocoral species may utilize chemical defenses to protect themselves against infection by strains of a known coral pathogen and contribute to the body of knowledge regarding the success of octocorals on Caribbean reefs.