Competition among sessile organisms on coral reefs

Abstract

Competition among sessile organisms is a major process on coral reefs, and is becoming more important as anthropogenic disturbances cause shifts in dominance to non-reef builders such as macroalgae, soft corals, ascidians, and corallimorpharians. Long-term monitoring and field experiments have demonstrated that competition for limited space can exert major impacts on reef biodiversity and community composition across habitats and regions. Recent experiments also reveal increasingly important roles of allelopathic chemicals and the alteration of associated microbes in shaping competitive outcomes among benthic space occupiers. Competition impacts the recruitment, growth, and mortality of sessile reef organisms and alters their population dynamics. Co-settlement and aggregation of conspecific coral colonies may lead to intense intraspecific competition, including chimera formation and potential somatic and germ cell parasitism. The complexity of competitive outcomes and their alteration by a wide variety of factors, including irradiance, water motion, and nutrient levels, results in mostly circular networks of interaction, often enhancing species diversity on coral reefs. Competition is a model process for revealing impacts of human activities on coral reefs, and will become increasingly important as alternate dominants gain space at the expense of reef-building corals. © 2011 Springer Science+Business Media B.V.