Behavior and physiology of coexistence in two species of Dascyllus (Pomacentridae,Teleostei)

Synopsis In the Gulf of Aqaba Dascyllus aruanus and D. marginatus, form distinct populations organised into harems of single males and groups of females, living permanently in Stylophora and Acropora corals. Each harem consists of 4 sexual casts: dominating males, adult females, sex-changing fish and juveniles. The sexual performance of each adult fish in such social units is controlled by the presence or absence of a dominating male. In corals occupied by mixed groups of both species, only those females spawn that belong to the same species as the dominating male. Direct observation in the sea shows that such situations are produced by indiscriminative settling mechanisms of groups of juvenile fish. Evidence is also presented, demonstrating that dispersion of coral colonies suitable for occupancy and predation by piscivorous fish can modulate such complicated reproduction.