Feasibility of ex situ cultivation and outplanting of the habitat-forming seaweed Ericaria selaginoides in an oceanic island: insight for future restoration

Marine forests formed by Cystoseira species are undergoing population declines across the Macaronesian archipelagos, threatening the essential ecosystem services they provide. Active restoration strategies, particularly ex situ cultivation and outplanting of early stages, are emerging as key tools to recover these habitats. We assessed the feasibility of restoration for the canopy-forming brown alga Ericaria selaginoides in the Canary Islands, combining laboratory-based optimization of seedling cultivation with a field outplanting experiment. Methods: To optimize early development, we conducted a factorial experiment testing the influence of two light intensities (125 and 250 μmol photons m−2s−1) and three culture media: filtered seawater (SW), Von Stosch (VS) solution, and a commercial Macrocystis derived bio-stimulant (Algatron Cifo® AL). Then juveniles were outplanted at two tidal heights (i.e., upper and lower intertidal) and under different microhabitat conditions (i.e., inside and outside tidal pools). Results: Embryos cultured with VS and SW had advanced embryonic development, while those grown under low light and VS medium reached significantly larger sizes at advanced stages, indicating enhanced growth potential. This combination of low light and VS medium was therefore selected to optimize juvenile cultivation. Field monitoring revealed strong environmental filtering. Survival and growth were highest in lower intertidal pools, while individuals in the upper, more exposed, zones experienced high mortality. Discussion: These findings demonstrate that ex situ cultivation of E. selaginoides, combined with strategic microhabitat selection, could enhance restoration success. These outcomes provide a scalable and practical solution for the long-term implementation of restoration techniques, offering initial insight into the recovery potential of Cystoseira forests in oceanic insular regions that suffered widespread declines.