Survivorship of fast-growing coral spats depend less on refuge structure: the case of Acropora solitaryensis

Previous studies have demonstrated the importance of refuge structure from grazers on settlement substrata in survivorship of scleractinian coral spats. The present study reports some evidence showing that the importance of refuges varies depending on growth speed of coral spats. Survival of spats of the fast-growing scleractinian coral, Acropora solitaryensis that had settled on plain surfaces of settlement plates or in artificially-made micro-crevices (MC) serving as refuges on the plain plate surfaces was monitored in situ over the first year of life. Survival rate of A. solitaryensis spats dropped rapidly to less than 50% during the first two months but stabilized afterward and maintained high values both in MC (33%) and on the plain surfaces (17%) by the end of the one year experimental period. The higher spat survival rate observed in MC confirmed refuge effects on spat survivorship while many spats surviving on plain surfaces, which were not seen in slow-growing coral species in a previous comparable study, suggest that spats of fast-growing coral species that can attain a large enough size to survive damage from grazers early may depend less on refuge structure on settlement substrata. This may allow fast-growing coral species to extend potential areas for successful recruitment, more regardless of surface structure of settlement substrata, promoting its population development.