Reproductive phenology and sexual propagation of the pink sea fan Eunicella verrucosa Pallas, 1766 for coral restoration

The widespread decline of coral-dominated ecosystems due to human disturbances has highlighted the urgent need for active habitat restoration. Coral restoration using sexually produced individuals instead of clonal fragments is essential to reduce impacts on donor populations and promote genetic diversity, which is vital for adaptability to environmental changes. However, for most coral species, particularly those in temperate and deep-water (> 50 m), critical knowledge of reproduction and larval ecology for ex situ sexual propagation is lacking. To address this gap, in this study, we provide the first report of spawning of the octocoral Eunicella verrucosa in the North-East Atlantic and describe details on larval development and settlement. The annual reproductive timing in South-West Portugal was determined from samples collected as fisheries bycatch from a single population source and monitored for comparison across distinct durations and conditions. The species exhibited split-spawning over about one month (mid September – mid October), with 3 major events approximately every 2 weeks. Spawning patterns suggest lunar periodicity but shifted between colonies kept in distinct conditions. Oocytes were positively buoyant and developed into swimming larvae after 3 days. Settlement trials using substrates like natural rock, CCA, and gorgonian skeleton, showed larvae behaviour testing the substrates about two weeks post-spawning, and settlement activity continuing over three months. Fully developed recruits were observed after one month, with sclerite production starting before tentacle development. New settlement continued for up to three months, indicating a prolonged competency period. This study provides crucial data for coral restoration efforts using ex situ sexual propagation of this vulnerable species.