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

The widespread decline of coral-dominated ecosystems 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 critical knowledge of reproduction and larval ecology for ex situ sexual propagation is lacking. To address this gap, this study presents the first report of spawning of the octocoral Eunicella verrucosa in the North-East Atlantic and describes larval development and settlement. The annual reproductive timing in South-West Portugal was determined from samples collected as fisheries bycatch from the same habitat and monitored for comparison across distinct durations and conditions. The species exhibited split spawning (three major events approximately every two weeks) over about one month (mid-September–mid-October). Spawning patterns can suggest lunar periodicity but shifted between colonies kept in distinct conditions. Oocytes were positively buoyant and developed into swimming larvae after three days. Settlement trials using substrates such as natural rock, crustose coralline algae (CCA), and gorgonian skeleton, showed larvae started testing the substrates about two weeks after spawning, with settlement activity continuing over up to three months. Fully developed recruits were observed after one month, with sclerite production starting before tentacle development. The observation of new larval settlement up to three months indicates a prolonged competency period. This study provides crucial data for coral restoration efforts using ex-situ sexual propagation of a vulnerable species.