On sexual reproduction and physiology of the soft coral Sclerophytum eilatensis (van Ofwegen, Benayahu & McFadden, 2013) along a depth gradient

Abstract The ability of species to thrive across environmental gradients relies on their ability for sexual reproduction and physiological adaptations to varying conditions. Advances in diving technologies have enabled in-depth research into coral ecology and biology along depth gradients, from shallow-water habitats to mesophotic coral ecosystems (MCEs; 30–150 m). Findings from such studies highlight the rich biodiversity found on MCEs and their extensive distribution. Additionally, studies suggest that MCEs may act as refugia for some shallow species, providing shelter from threats such as marine heatwaves. Effective refugia require that individuals within a population can both reproduce sexually and adapt physiologically along their depth range. The present study investigates the reproductive biology and physiological traits of the zooxanthellate octocoral Sclerophytum eilatensis (Malacalcyonacea, Sarcophytidae) along a depth gradient down to 65 m in the Gulf of Aqaba/Eilat. By examining its sexual reproduction and the physiological parameters of both coral host and its symbionts, our findings provide a glance into this octocoral’s adaptive nature. We demonstrate that MCEs offer favorable conditions for S. eilatensis sexual reproduction. However, significant variations in reproductive and physiological characteristics along depth underscore the necessity for careful evaluation of the potential for MCEs to facilitate the recovery of shallow-reef populations. The study highlights the importance of both reproduction and physiological studies in order to advance our understanding of coral adaptation and resilience in changing marine environments.