Size-dependent dominance hierarchy in the anemone Actinia equina

THERE are many examples of aggression among anthozoan coelenterates: corals show interspecific interaction in which ranking may be obvious1, and inter-clonal aggression occurs in the anemone Anthopleura elegantissima2. Aggressive behaviour is also exhibited by some solitary anemones, such as Actinia equina L. Both these species possess special structures bearing batteries of nematocysts, the acrorhagi which are used solely for offence3. We report here that there is a hierarchy of aggression, which is based on size, in A. equina.