Competition between scleractinian corals and macrolagae is a key ecological process in coral reefs, especially during reef degradation. From the numerous studies on these ecological interactions we have learned that positive and negative interactions (1) are species-specific and (2) vary in relation to the life stages. Extrapolation of ecological studies with doubtful taxonomic identification and no biological data are therefore very dangerous. Additionally, we have recently become aware that biotic interactions happen between holobionts, and consequently all players, host and associated microbial community, should be considered in ecological studies. It is only recently, that the microbial component has been considered in the interactions between macroalgae and corals, and we have only begun to scratch the surface of the complex interaction mechanisms between these two important holobiont taxa. Taking the model organism Lobophora we will study the interactions between macroalgae-corals-herbivores-microbes in greater depth. The present research project intends to (1) provide a documentation of the life history stages of several species of Lobophora naturally found in contact or not with corals, (2) document the microbial community (and epiphytes) associated with different Lobophora species at different life stages, and (3) implement chemical ecology experiments to study the ecological interaction between Lobophoraand coral-holobionts, and herbivores.