Effects of seeding method, timing and site selection on the production and quality of sugar kelp, Saccharina latissima: A Danish case study

In recent years, research projects and enterprises have documented that the sugar kelp, Saccharina latissima, can be successfully cultivated in Northern European waters. There is a need however, for optimizing production methods to achieve an economically viable and competitive business. A novel direct seeding method, applying juvenile sporophytes directly onto textiles immediately before deployment, could be part of the optimization, as it obviates the nursery process, and can be combined with novel seeding materials, such as non-woven textiles. An extensive comparison of biomass yield and quality was made between direct and traditional seeding methods and substrates, including three deployment campaigns in three different cultivation sites: Textile ribbons were directly seeded with juvenile sporophytes (<1 mm size), and deployed the following day, whereas kuralone twine was traditionally seeded with spores, and deployed after a nursery period. The seeded materials were deployed in September, October and November, at Hjarnø and Limfjorden, and in November at the Grenaa site. The direct seeding method gave yields comparable to the traditional seeding method (1.0 ± 0.1 kg FW m⁻¹ and 1.0 ± 0.2 kg FW m⁻¹, respectively) at the most exposed site, whereas at the sheltered sites, the direct seeding method only resulted in a measurable yield following the October deployment. The highest biomass yield was achieved using the traditional seeding method, deployed in September in the Limfjorden (1.6 ± 0.4 kg FW m⁻¹). The biomass quality was not affected by seeding method, but differed significantly between sites, with biomass from the Limfjorden having the highest content of nitrogen (4.65 ± 0.07% N of DM) and the lowest content of iodine (1.612 ± 271 mg I kg⁻¹ of DM). In future cultivation practices, the direct seeding method could be implemented in exposed locations in Danish waters, whereas for the more sheltered/turbid waters, improvements are needed for the direct seeding technique to become feasible.