Journal Article
Exploring uncharted waters of future crop systems: Pioneering Ulva intestinalis seedling development for a sustainable full-life-cycle offshore aquaculture in the wider Baltic Sea area
Sophie Steinhagen; Swantje Enge; Elena Schrofner-Brunner; Inga Hellige; Ida Johansson; Göran Nylund; Annelous Oerbekke; Katharina Romoth; Eva Strothotte; Tim Staufenberger; Mirco Kaiser; Teis Boderskov; Annette Bruhn
Journal of Applied Phycology · Vol. 38, Issue 3 · pp. 2111-2126 · 2026
Abstract
Ulva intestinalis has been proposed as a promising candidate for seaweed aquaculture in the Baltic Sea due to its wide environmental tolerance and fast growth. This study evaluates the full life-cycle cultivation potential of U. intestinalis , from strain selection, fertility induction and seedling development to offshore biomass production, using 40 strains from ecologically distinct Baltic locations. Fertility was successfully induced in only 10% of the strains, underscoring the need for targeted screening and optimized induction protocols for potential aquaculture strains combined with subsequent biobanking strategies. In successfully induced strains, gametogenesis proceeded in a synchronized three-day cycle, with rapid and uniform ontogenetic development observed across salinity origins. Offshore cultivation trials at two sites (Koster archipelago, Sweden and Kriegers Flak, Denmark) confirmed the feasibility of nursery-based pre-cultivation in combination with sea-based farming for biomass production. However, the lower biomass yield but relatively faster growth of this species compared to foliose Ulva spp. may require more frequent harvesting, which must be evaluated against the operational constraints of offshore sites. Although co-location with existing offshore infrastructure could mitigate spatial competition, the economic feasibility of U. intestinalis cultivation ultimately depends on aligning biological performance with efficient nursery production and practical harvesting strategies. Strain-specific characteristics relevant to intended markets may support an advantage for nearshore production sites. The here developed techniques demonstrate that U. intestinalis can be successfully cultivated from gametes to seeded crops in Baltic sea-based environments, establishing a proof-of-concept for its integration into Baltic aquaculture systems.