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.
Highlights
Coral reefs are facing intensifying threats worldwide, largely due to chronic and acute environmental variability or anthropogenic disturbers
Larval metamorphosis was higher in the treatments with the presence of living or dead crustose coralline algae (CCA) chips than in the other treatments, either in the nochoice experiment or in the paired-choice experiment
These experiments showed a wide range of number of larvae settled among replicates in each treatment, but the overall rates of metamorphosis were higher in choice experiments than that observed in no-choice experiments
Summary
Coral reefs are facing intensifying threats worldwide, largely due to chronic and acute environmental variability or anthropogenic disturbers. Several laboratory studies suggest that numerous coral larvae preferred to select particular species of crustose coralline algae (CCA) as their settlement substrate Some coral larvae settle and metamorphose in response to the microbiological (epiphytic microbial biofilm) (Webster et al 2004, Sneed et al 2014) and chemical (Sneed et al 2014, Tebben et al 2015) cues of CCA. Not all species of CCA facilitate larval settlement and some studies show CCA is not required for coral larval settlement (Ritson-Williams et al 2010). Study reported some coral larvae may use spectral cues for fine-scale habitat selection during settlement (Mason et al 2011). The inducing cues involved in the inherent feature of CCA had been overlooked in some extent
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