Quantification of larval traits driving connectivity: the case of Corallium rubrum (L. 1758)

Larval dispersal is the process enabling connectivity between populations of marine species with a sedentary adult stage. This transportation results from the coupling between flow and larval biological traits. This experimental study aims to quantify these larval biological traits, namely pelagic larval duration (PLD), buoyancy and larval vertical motility behavior, for Corallium rubrum. Larval vertical motility behavior was split into active behavior (swimming) and passive behavior (free fall). A particle-tracking routine was applied to video recordings of the active and passive motility behavior of C. rubrum larvae to quantify their free fall speeds, swimming activity frequency and swimming speeds. The experiment was repeated under different light conditions and at different larval ages. PLD ranged from 16 days (95 % survival) to 42 days (5 % survival). Larvae exhibited negative buoyancy with a free fall speed decreasing linearly with age, at a velocity varying from −0.09 ± 0.026 cm s−1 on day 1 to −0.05 ± 0.026 cm s−1 on day 10. No significant difference was found either in the activity frequency or in the mean swim velocities during active periods for age (up to 12 days old) or under different light conditions. C. rubrum larvae maintained active swimming behavior for 82 % of the time. This activity frequency was combined with age-varying free fall periods in the motility behavior model extrapolated up to 15 days old, resulting in a mean upward speed that increased from 0.045 cm s−1 (day 1) to 0.056 cm s−1 (day 15). This larval motility behavior, combined with the extended PLD, confers on C. rubrum larvae an unsuspectedly high dispersive potential in open waters.