Shedding new light on scleractinian coral recruitment

Studies of the distribution of scleractinian coral recruits within stacks 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 surfaces 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 towards the center. Growth and survivorship of hermatypic corals were dependent 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 stacks 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 positions of coral spat. In the absence of evidence for selective hydrodynamic deposition of spat, these results suggest that light intensity is the most important factor in determining the position of attachment of coral spat on the underside of these plates.