Selection preferences of late brachiolaria larvae of Acanthaster solaris for benthic habitats

The outbreaks of the crown-of-thorns starfish (CoTS; Acanthaster spp.) are a significant cause of coral reef ecosystem degradation worldwide. The settlement process is a crucial phase in the life history of CoTS, marking the transition from a planktonic to a benthic lifestyle. The choice of suitable benthic habitat for settlement significantly impacts the survival, growth, population distribution, outbreak intensity, and range of CoTS larvae/juveniles. In this study, pairwise choice experiments were conducted to examine the settlement preferences of late brachiolaria larvae of Acanthaster solaris for different benthic habitats. Results revealed that the larvae exhibited significant preferences (P＜0.05, Chi-square test) for crustose coralline algae (CCA), Acropora hyacinthus, and coral skeletons over plain rubble, with the preference order being: CCA＞Acropora＞coral skeletons＞benthic rubble. However, the larvae demonstrated significant avoidance behavior (P＜0.05, Chi-square test) when encountering Acropora hyacinthus with Trapezia crabs and adult starfish. Results indicated that the settlement rate of brachiolaria larvae in the CCA habitat reached 91.67% at 48 hours, significantly higher than that in the benthic rubble (63.33%) and coral skeleton (71.67%) habitats (P＜0.05, one-way ANOVA). The findings indicate that late brachiolaria larvae of CoTS possess the ability to perceive benthic habitats and actively select habitats for settlement, with a strong preference for CCA, which also yielded the highest settlement rate. The study provides a foundational understanding of the settlement process of CoTS larvae, the spatial distribution characteristics of benthic juveniles, and the mechanisms underlying CoTS outbreaks.