The effect of light intensity and tidal cycle on the hatching and larval behaviour of the muricid gastropod Chorus giganteus

Encapsulation is a common strategy observed among marine caenogastropods. Although the capsule confers protection for embryos, its rigidity and strength pose a significant challenge as the larvae hatch. The factors that drive hatching among these benthic marine gastropods have scarcely been studied. In this study, we experimentally evaluated whether the capsule plug opening and larval release processes were synchronised with day/night or tidal cycles in the muricid gastropod Chorus giganteus. In addition, we tested the effect of different levels of light intensity on the swimming behaviour of pre- and post-hatching larvae. The results showed that capsule plug rupture occurred in synchronous pulses of capsule groups during both day and night. A periodogram analysis did not show circatidal rhythmicity in either the plug rupture or total number of capsules hatched. The highest percentage of larvae hatched at sunset and during the night (82.9%), whereas only 17% of them hatched during the day. These results demonstrate a circadian pattern. The swimming activity of the larvae decreased significantly with light intensity. In the darkness, over 80% of the larvae actively swam in the tank and the majority of the larvae initially moved toward the water surface. No swimming activity was observed at 500μE*m^-2*s^-1 of photon flux density. These results suggest that C. giganteus larvae present negative phototropism behaviour and that capsule plug degradation occurs by other processes like internal physical enzymatic actions.