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 cultivatedU. fenestratadepends 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.
Highlights
A central, recurring, and utmost important issue of the 21st century is the urgent need for new, sustainable future resources to supply a constantly growing world population
Based on this first morphological variation of the biomass, the total yield, general thallus habitus, and the amount of biofoulers was determined: The biomass yields significantly increased during the early growth season and reached its maximum at the third harvest time at DOY = 141
Similar patterns have been observed for the thallus area which significantly increased from 682.07 cm2 at the first harvest point to 1216.63 cm2 at the third harvest time point at DOY = 141 (Figures 1C, 2B and Table 1C)
Summary
A central, recurring, and utmost important issue of the 21st century is the urgent need for new, sustainable future resources to supply a constantly growing world population. The necessity of the provision of renewable and novel materials and nutritious food sources – especially vegetarian and vegan protein – was emphasized by the United Nations Sustainable Development Goals (SDGs) (UN General Assembly, 2015). These goals were intensely reflected by the European Commission’s. Van Krimpen et al (2013) showed that seaweed farms can produce more protein per hectare compared to soy: 2.5–7.5 tons/ha vs 0.6– 1.2 tons/ha (Van Krimpen et al, 2013), making it a very interesting protein crop Another important benefit of seaweed biomass is its multi-purpose application in different economic sectors (Hafting et al, 2015; FAO, 2018). The cultivation of extractive aquatic species, like seaweeds, is accompanied by various ecosystem and bioremediation services such as the uptake of dissolved nutrients, coastal defense, and carbon sequestration (e.g., Araújo et al, 2021)
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