Algal chemical ecology in a changing ocean

Abstract

Macroalgae and benthic cyanobacteria are becoming increasingly abundant on reefs, and many of these dominant algae produce diverse secondary metabolites. Abundant brown and green macroalgae and nuisance blooms of cyanobacteria occur regularly throughout Florida and on the Belizean barrier reef. Crude extracts and compounds from some macroalgae and cyanobacteria deter feeding by natural assemblages of fishes and the sea urchin Diadema antillarum. In addition, macroalgal and cyanobacterial secondary metabolites may serve multiple ecological functions, including inhibition of microorganisms and competition for space. The role of allelopathy (chemical inhibition) in mediating the interactions between chemically rich species of algae and cyanobacteria and different life history stages of corals was tested. Extracts and isolated compounds from Dictyota spp., Lyngbya spp. and other cyanobacteria negatively influenced the settlement and metamorphosis of coral larvae. On reefs experiencing increased abundance of chemically defended macroalgae and benthic cyanobacteria, the restocking of adult coral populations may be slowed due to recruitment inhibition caused by algal secondary metabolites. These compounds protect some algae from herbivory (allowing increased space occupation) and reduce coral recruitment, both of which may perpetuate a “phase shift” from coral to algal dominated communities.