A scotophobic response characterised by body contraction and ciliary arrest in Acropora coral larvae
The motile planula larva of the reef-building coral Acropora millepora exhibits a distinct scotophobic response characterized by full-body contraction and ciliary arrest when exposed to abrupt light dimming. Through behavioural assays, we confirmed reductions in larval swimming speed and alterations in vertical and horizontal movement patterns under alternating light and dark conditions. High-speed microscopic imaging revealed that ciliary activity ceases upon light dimming, while the body contracts into a rounded shape, influencing swimming behaviour. These responses suggest an adaptive mechanism for maintaining optimal positioning within the highly structured and complex light environment of reef habitats, critical for coral recruitment and survival.