MEPS prepress abstract  -  doi: 10.3354/meps07418

ABSTRACT: Diseases of marine organisms, and corals in particular, have been reported with increasing frequency over the past three decades. Although little is known about resistance to disease in corals, one potential mechanism of defense is the production of antimicrobial compounds that protect corals from microbial pathogens. We assessed antibacterial activity of crude aqueous extracts from three common Hawaiian reef corals, Montipora capitata, Porites lobata and Pocillopora meandrina, against nine strains of bacteria. The bacteria selected included known coral pathogens, potential marine pathogens found in human waste and bacteria previously identified from the surfaces of Hawaiian corals. Extracts from all three coral species exhibited high levels of antibacterial activity. Overall, 54.3% of assays resulted in bacterial growth inhibition. In addition, 9.9% of extracts stimulated the growth of certain bacteria. Although levels of overall antibacterial activity did not differ significantly among coral species (ranging from 40.7% of assays for Pocillopora meandrina to 63.0% of assays for Montipora capitata), the three species exhibited a high degree of selectivity as demonstrated by significant variability in their effects towards specific bacteria. Extracts also exhibited intraspecific variability, both within and between sites, and significant site-by-species interactions were observed against six out of nine bacterial strains. In M. capitata, healthy corals had significantly higher levels of antibacterial activity than those affected by Montipora White Syndrome, and affected tissues had significantly higher levels of antibacterial activity than unaffected tissues. Variability in antibacterial activity of Hawaiian corals may, in part, explain differential susceptibility to disease at the colony, species or population level.