Harmful algae on tropical coral reefs: Bottom-up eutrophication and top-down herbivory

A conceptual paradigm, the ‘‘Relative Dominance Model’’, provides the perspective to assess the interactive external forcingmechanisms controlling phase shifts among the dominant benthic functional groups on tropical coral reefs [i.e., microalgal turfs and frondose macroalgae (often harmful) versus reef-building corals and calcareous coralline algae (mostly beneficial due to accretion of calcareous reef framework)]. Manipulative experiments, analyses of existing communities and bioassays tested hypotheses that the relative dominances of these functional groups are mediated by two principal controlling factors: nutrients (i.e., bottom-up control) and herbivory (i.e., top-down control).