SHEDDING NEW LIGHT ON SCLERACTINIAN CORAL RECRUITMENT

Studies of the distribution of scleractinian coral recruits within sta cks of settlement plates at Orpheus Island and Lizard Island revealed that corals are recruited almost exclusively on the lower surfaces of the settlement plates. The absence of recruitment on the upper surface s of the plates is attributed to the observed high levels of sediment on these surfaces. All hermatypic coral spat were found near the edge of the settlement plates, whereas ahermatypic corals were located towa rds the center. Growth and survivorship of hermatypic corals were depe ndent on the position of attachment, decreasing with distance from the edges of the plates. Survivorship of ahermatypic corals was uniformly high. Light levels on the lower surfaces of the plates within the sta cks were shown to decay asymptotically as a function of distance from the plate edge. There was a highly significant non-linear relationship between relative light intensity on the settlement plates and the pos itions of coral spat. In the absence of evidence for selective hydrody namic deposition of spat, these results suggest that light intensity i s the most important factor in determining the position of attachment of coral spat on the underside of these plates.