Competetive exclusion of common scleractinians by solitary Anemone anemonia Manjano (Carlgren) on coral reefs of the Central Vietnam

An outbreak of actiniarian Anemonia manjano (Carlgren) was observed by 2013 and 2014 on shallow fringing coral reefs (2-6 m depth) at Hon Tre and Hon Cau islands (Central Vietnam). The anemone occupied all types of reef substrata: rubble, sand, old dead corals and living coral colonies. The clear tendency for this anemone to overgrow reef-building corals from Acropora, Porites and Millepora genera with partial mortality of coral polyps in the contact zones is discovered. Corymbose or caespitose growth forms of Acropora with short and thin branches are affected more than arborescent Acropora muricata with long cylindrical branches. Among non-skeletal Hexacorallia outcompeting reef-building stony corals the representatives of Corallimorpharia order are mostly reported to be responsible for local phase shifts to alternative benthic communities on coral reefs. The present study showed that the representatives of Actiniaria order as well as corallimorpharians may successfully replace stony corals in coral reef communities under the impact of natural and anthropogenic disturbances.