Competitive strategies of soft corals (Coelenterata: Octocorallia): III. Spacing and aggressive interactions between alcyonaceans

Abstract

Interactions were observed in the field between neighboring colonies of the alcyonacean octocoral Sinularia flexibilis (Quoy & Gaimard) and Sinularia sp., as well as between Sarcophyton glaucum (Quoy & Gaimard) and Sinularia sp. Visible effects observed included growth modification, stunting, scarring, and bleaching. Allelopathy was suspected as the cause. An experiment was performed to examine the responses of certain alcyonaceans to each other in competition for space and possible causes of the observed effects. Specimens of 3 species of erect soft corals (Sinularia flexibilis, Nephthea sp., and Alcyonium molle Dean) were collected and relocated in pairs under both contact and non-contact (close proximity) conditions at a depth of 3 to 5 m in Pioneer Bay, Orpheus Island, Queensland (18"40'S. 145"30' E). Initial effects observed included tissue necrosis and destruction of polyps, especially in contact situations, followed by colony reorientation. Long-term visible damage was minimal because, in all cases, the colonies subsequently moved apart. These sessile organisms exhibit a spacing behaviour allowing them to maintain an 'individual distance' in the same manner a s many sedentary or vagile organisms. This decreases the incidence of aggression and potentially destructive interactions Alcyonacean corals possess numerous adaptations which allow them to survive both predation and competition for space.