Latitudinal, seasonal and depth-dependent variation in growth, chemical composition and biofouling of cultivated Saccharina latissima (Phaeophyceae) along the Norwegian coast

Abstract

The Norwegian coastline covers more than 10°in latitude and provides a range in abiotic and biotic conditions for seaweed farming. In this study, we compared the effects of cultivation depth and season on the increase in biomass (frond length and biomass yield), chemical composition (protein, tissue nitrogen, intracellular nitrate and ash content) and biofouling (total cover and species composition) of cultivated Saccharina latissima at nine locations along a latitudinal gradient from 58 to 69°N. The effects of light and temperature on frond length and biofouling were evaluated along with their relevance for selecting optimal cultivation sites. Growth was greater at 1-2 m than at 8-9 m depth and showed large differences among locations, mainly in relation to local salinity levels. Maximum frond lengths varied between 15 and 100 cm, and maximum biomass yields between 0.2 and 14 kg m −2. Timing of maximum frond length and biomass yield varied with latitude, peaking 5 and 8 weeks later in the northern location (69°N) than in the central (63°N) and southern (58°N) locations, respectively. The nitrogen-to-protein conversion factor (averaged across all locations and depths) was 3.8, while protein content varied from 22 to 109 mg g −1 DW, with seasonality and latitude having the largest effect. The onset of biofouling also followed a latitudinal pattern, with a delayed onset in northern locations and at freshwater-influenced sites. The dominant epibiont was the bryozoan Membranipora membranacea. Our results demonstrate the feasibility of S. latissima cultivation along a wide latitudinal gradient in North Atlantic waters and underscore the importance of careful site selection for seaweed aquaculture.

The Effect of Nutrient Availability and Light Conditions on the Growth and Intracellular Nitrogen Components of Land-Based Cultivated Saccharina latissima (Phaeophyta)

“…This storage capability is, however, found to be relatively low, constituting only a small fraction (3.6%) of the maximum Q N content for the D4 treatments. This level of I-DIN agrees with earlier field studies and an experiment made to characterize nitrate uptake kinetics of S. latissima (Forbord et al, 2020(Forbord et al, , 2021. Even though the value of I-DIN is low, the variable correlates well with other nitrogen metabolites and growth rate.…”

“…The highest measured protein content of 77.0 ± 2.7 mg g −1 DW (median ± MAD), found for the D4 treatment, was higher or similar to values registered in May-June for S. latissima in several other experiments using the same estimation method based on amino acids (Marinho et al, 2015;Bak et al, 2019;Forbord et al, 2019Forbord et al, , 2020. The D4 sporophytes had almost twice the protein content compared to the surface water treatments.…”

“…Some uncertainty is connected with the use of K p factors, because they may change with season, depth, location and species. K p factors have been shown to vary in the range of 2.0-6.25 (Lourenço et al, 2002;Schiener et al, 2015;Angell et al, 2016;Biancarosa et al, 2017;Manns et al, 2017;Sharma et al, 2018;Bak et al, 2019;Forbord et al, 2020). The 6.25 value is the standard factor used for pure protein and is obviously not relevant for biomass samples that contain other N-rich components like nucleic acids and pigments.…”

“…The nitrogen component was used to calculate the protein content of the samples by using a nitrogen-to-protein conversion factor (K p ) of 3.8. This factor was determined based on measurements of total amino acids for locally cultivated S. latissima sporophytes (Forbord et al, 2020). Protein results that are further discussed in this article are based on this method.…”

“…Seaweed cultivation is increasing rapidly along the North Atlantic coasts (Stévant et al, 2017;Grebe et al, 2019;Forbord et al, 2020), while farming of seaweed has been an established industry for decades in many Asian countries, producing over 30 million metric tons per year (FAO, 2020). Seaweed biomass is mainly used for human consumption and in the phycocolloid industry, but it also has a wide range of applications as feed ingredients, fertilizers, biofuels, and biochemicals (Skjermo et al, 2014;Barbier et al, 2019;Buschmann and Camus, 2019).…”