Harvest Time Can Affect the Optimal Yield and Quality of Sea Lettuce (Ulva fenestrata) in a Sustainable Sea-Based Cultivation

Abstract

Seaweed biomass is a renewable resource with multiple applications. Sea-based cultivation of seaweeds can provide high biomass yields, low construction, operation, and maintenance costs and could offer an environmentally and economically sustainable alternative to land-based cultivations. The biochemical profile of sea-grown biomass depends on seasonal variation in environmental factors, and the optimization of harvest time is important for the quality of the produced biomass. To identify optimal harvest times of Swedish sea-based cultivated sea lettuce (Ulva fenestrata), this study monitored biomass yield, morphology, chemical composition, fertility, and biofouling at five different harvesting times in April – June 2020. The highest biomass yields (approximately 1.2 kg fw [m rope]–1) were observed in late spring (May). The number and size of holes in the thalli and the amount of fertile and fouled tissue increased with prolonged growth season, which together led to a significant decline in both biomass yield and quality during summer (June). Early spring (April) conditions were optimal for obtaining high fatty acid, protein, biochar, phenolic, and pigment contents in the biomass, whereas carbohydrate and ash content, as well as essential and non-essential elements, increased later in the growth season. Our study results show that the optimal harvest time of sea-based cultivated U. fenestrata depends on the downstream application of the biomass and must be carefully selected to balance yield, quality, and desired biochemical contents to maximize the output of future sea-based algal cultivations in the European Northern Hemisphere.

Closed life-cycle aquaculture of sea lettuce (Ulva fenestrata): performance and biochemical profile differ in early developmental stages

“…Assessments of the fatty acid content and composition of lyophilized U. fenestrata juveniles followed a direct transesterification method which was successfully applied in previous studies on Ulva biomass (see also Toth et al, 2020;Steinhagen et al, 2021;Steinhagen et al, 2022) and was described in detail by Harrysson et al (2018). We used C17:0 as internal standard for quantification and identification of fatty acids was done using GLC-463 Reference standards (Nu-Check Prep, Inc.).…”

“…Ulva biomass has recently gained attention in several economic sectors due to its multipurpose use in commodity products which is favored by their different high-value biochemical compounds (Holdt and Kraan, 2011;Toth et al, 2020;Olsson et al, 2020b). It has been shown by several previous studies that varying abiotic factors in cultivation settings influence the biochemical content of adult Ulva biomass (Holdt and Kraan, 2011;Toth et al, 2020;Olsson et al, 2020b;Steinhagen et al, 2022), but knowledge on the effect on early lifehistory-stages is until date lacking. The protein content (14.9-29% dw) measured in the juvenile biomass of U. fenestrata was in an average range compared with previous studies on Ulva spp.…”

“…temperature, salinity, eutrophication) (Steinhagen et al, 2019a;Steinhagen et al, 2019b), which offers excellent qualities as crop species for the emerging Blue Economy at a global scale. Cultivation oriented research especially on the foliose shaped sea-lettuce-type of Ulva has increased during the past ten to fifteen years (Califano et al, 2020;Toth et al, 2020;Steinhagen et al, 2021;Steinhagen et al, 2022). Foliose species of Ulva are mostly maintained in free-floating cultures and are cultivated near-or on-shore (Hafting et al, 2015) in tanks (Toth et al, 2020), bioreactors (Sebök et al, 2019), basins (e.g.…”

“…Foliose species of Ulva are mostly maintained in free-floating cultures and are cultivated near-or on-shore (Hafting et al, 2015) in tanks (Toth et al, 2020), bioreactors (Sebök et al, 2019), basins (e.g. paddle-wheel basins) (Amosu et al, 2016) or ponds (Califano et al, 2020) and more recently also off-shore (Steinhagen et al, 2021;Steinhagen et al, 2022). Due to the increasing interest of the European seaweed sector in the aquaculture of Ulva specieswhich is based on the combination of above named compelling traits for cultivation and biomass valorizationupscaling processes, novel large-scale farming techniques, and closed life-cycle crop systems are needed.…”

“…U. fenestrata is a putative crop species in the Northern Hemisphere (Steinhagen et al, 2021;Steinhagen et al, 2022) where it is abundantly present in marine water bodies (Hughey et al, 2019;Steinhagen et al, 2019a). Individuals can be found in the sublittoral and are mainly present during Northern Hemisphere spring to summer conditions, whereas especially during summer conditions fertile margins of mature individuals could be observed.…”