Adherence of kelp (Saccharina latissima) gametophytes on ropes with different binder treatments and flow regimes

Abstract

The cultivation of kelp typically involves two stages, where an indoor hatchery phase preceedes the grow-out phase at-sea. The in situ adhesion of microscopic propagules onto specifically designed substrates using binders has been proposed as an alternative to conventional hatchery methods where juvenile seaweeds are cultured on seeded twine, aimed at saving resources while increasing productivity as it obviates the hatchery phase. Here we tested how well kelp (Saccharina latissima) gametophytes adhere to cultivation ropes using two binder types (agar and κ-carrageenan) and application treatment (separate or mixed application) under two ecologically relevant flow regimes (5 and 15 cm s−1), and a control condition (0 cm s−1) in a laboratory flume. Our findings indicate that the effectiveness of a binder to retain S. latissima gametophytes onto cultivation rope, measured by the sporophyte density, was comparable for all binder types in the high flow velocity (15 cm s−1) treatments, including the non-binder control treatment. Sporophyte densities were highest in the low flow velocities (0 and 5 cm s−1) in the absence of a binder compared to all other treatment combinations. In conclusion, our results highlight that the effectiveness of binder assisted seeding of kelp propagules did not differ between the binder and non-binder treatments and was unaffected by flow velocities for the binder treatments. These findings are important in the development of novel methods and further optimisation of existing binder-based methods aimed at retaining seaweed propagules onto cultivation rope.

Nature-based coastal restoration: Development of an early-rearing production protocol of sugar kelp (Saccharina latissima Linnaeus) for bottom planting activities in the Gulf of St-Lawrence (Québec, Canada)

“…no observable biomass differences. Visch et al (2023), in a controlled laboratory study, did not observe any effect on seeding of kelp (S. latissima) propagules of a binder (agar and kcarrageenan) nor an effect of flow velocity (0, 5 and 15 cm s -1 ) for the binder treatments.…”

“…Overall, the presence of the binder did not induce significant differences in density, but its use is still recommended given our needs of fast deployment at sea and the possible prevention, according to Lemoine and Lemaire (2019) of gametophyte desiccation between the time gametophytes are sprayed on the substrates and the time the substrates are effectively launched at sea, which could take several hours. To optimize efforts related to the transfer of young seedlings from hatchery to sea and ultimately to reduce time and cost in the hatchery, many studies tested the use of a binder treatment (Kerrison et al, 2018;Kerrison et al, 2020;Solvang et al, 2021;Visch et al, 2023). Many authors including Forbord et al (2020), strongly advocate the virtues of using a binder, arguing that it is widely used by commercial farms and in research projects and that it is 100× more space-efficient during the laboratory phase of the production cycle as it promotes the strength and resilience of the attachment to the substrate and rapid deployment at sea (Xu et al, 2009;Forbord et al, 2018;Kerrison et al, 2018); rendering the period of pre-growth of seedling unnecessary.…”

“…Sugar kelp seeding methods were first developed to meet the requirements and constraints of the aquaculture sector. Spores or gametophytes are usually seeded on ropes and then cultured in a controlled environment weeks before deployment at sea or, more recently, directly seeded with a binder just before deployment based on the premise that the high viscosity of the product would prevent the sporophytes from being washed away before the holdfast would attach to gametophyte-seeded twine or ropes (Forbord et al, 2020;Fredriksen et al, 2020;Visch et al, 2023) and that it could potentially protect the gametophytes from dehydration during transfer operations (Lemoine and Lemaire, 2019). This method could potentially decrease the time and cost associated with culture of sporophytes in controlled environments.…”

The sugar kelp Saccharina latissima II: Recent Advances in farming and applications

“…They concluded that these differences are expected to impact the biochemical composition of the biomass and that the seeding method should be selected depending on the end use of the biomass. Another study tested two binder types (agar and κ-carrageenan) under two ecologically relevant flow regimes (5 and 15 cm s −1 ) and a control condition (0 cm s −1 ) in a laboratory flume (Visch et al 2023). The results show no differences in results between the binder and non-binder treatments, and the results were also unaffected by the different flow velocities.…”