Coral larval settlement and post-settlement survival facilitated by crustose coralline algae with or without living tissue

Abstract

Selection of a permanent attachment site of coral larvae can be a critical determinant of recruitment success affecting the structure of coral communities and underpins the ability of coral reef ecosystems to recover from disturbance. Settlement specificity of a threatened coral in Sanya reefs, Acropora millepora, was tested by measuring the larval metamorphosis preferences and post-settlement survival in response to crustose coralline algae (CCA) species Hydrolithon reinboldii and other substrata. In the no-choice experiments, the larvae of A. millepora had similar rates of total metamorphosis with the presence of CCA regardless of the algae tissue being alive or not, and settlement success induced by CCA was higher than by other substrata (tile or glass). In the paired-choice experiments, when CCA was in presence, the coral larvae preferred the surface of the dish and the side of living CCA. In the absence of CCA, total larvae metamorphosis was lower than in the treatments where CCA was present. New recruits of A. millepora had approximately 68% mean survival on all the settlement substrata after 2 weeks maintained in aquaria with flow-through seawater similar to the coral larval sampling site, but with no coral spat survival in the treatments where CCA was absent. However, there were statistical differences between the larvae survival of dead CCA and glass chips treatment and the others where CCA was present. Our results were consistent with the conclusion that some CCA species could facilitate coral larval settlement and post-settlement survivorship, highlighting the importance of substrata selection success for facilitating coral recruitment in the threatened coral reefs.