Ulva fenestrata is an economically and ecologically important green algal species with a large potential in seaweed aquaculture due to its high productivity, wide environmental tolerance, as well as interesting functional and nutritional properties. Here, we performed a series of manipulative cultivation experiments in order to investigate the effects of irradiance (50, 100, and 160 μmol photons m−2 s−1), temperature (13 and 18 °C), nitrate (< 5, 150, and 500 μM), phosphate (< 1 and 50 μM), and pCO2 (200, 400, and 2500 ppm) on the relative growth rate and biochemical composition (fatty acid, protein, phenolic, ash, and biochar content) in indoor tank cultivation of Swedish U. fenestrata. High irradiance and low temperature were optimal for the growth of this northern hemisphere U. fenestrata strain, but addition of nutrients or changes in pCO2 levels were not necessary to increase growth. Low irradiance resulted in the highest fatty acid, protein, and phenolic content, while low temperature had a negative effect on the fatty acid content but a positive effect on the protein content. Addition of nutrients (especially nitrate) increased the fatty acid, protein, and phenolic content. High nitrate levels decreased the total ash content of the seaweeds. The char content of the seaweeds did not change in response to any of the manipulated factors, and the only significant effect of changes in pCO2 was a negative relationship with phenolic content. We conclude that the optimal cultivation conditions for Swedish U. fenestrata are dependent on the desired biomass traits (biomass yield or biochemical composition).

Seaweed biomass has the potential to become an important raw material for bio-based production. The aim of this study was to screen the overall composition of several seaweed species on the Swedish west coast, including some scarcely studied species, to provide fundamentals for evaluation of biorefining potential and to benchmark with already potentially industrially relevant species and commercially important land-based biomasses. Twenty-two common seaweed species (green, red, brown) were collected and the carbohydrate, ash, protein, water and metal contents were measured. Carbohydrate content varied between 237 and 557 g kg−1 dry weight (dw), making it the largest constituent, on a dry weight basis, of most species in the study. Ash, which is considered unwanted in biorefining, ranged between 118 and 419 g kg−1 dw and was the largest constituent in several seaweeds, which were therefore considered unsuitable for biorefining. Protein content was most abundant in the red seaweeds but was generally low in all species (59–201 g kg−1 dw). High contents of several unwanted metals for processing or human consumption were found (e.g. aluminium, arsenic, copper, chromium and nickel), which need to be considered when utilizing seaweeds for certain applications. Potential targets for further biorefinery development mostly include species already known for their potential (Saccharina latissima, Laminaria digitata and Chondrus crispus) while some, such as Halidrys siliquosa and Dilsea carnosa, have not been previously noted. However, more detailed studies are required to explore biorefinery processes for these seaweeds, as well as how to potentially cultivate them.

Seaweed cultivation and processing industries could contribute to sustainable blue growth and the European bioeconomy. This article contributes a case study evaluation of environmental sustainability of preserved brown seaweed Saccharina latissima by means of environmental life cycle assessment of a pilot facility in Sweden. The study accounts for nutrient bioremediation and carbon capture and includes two alternative hatchery processes, a 2-ha longline cultivation, and four alternative preservation methods (hang-drying outdoors, heated air-cabinet drying, ensiling, and freezing). The study found that as a result of carbon capture and nitrogen and phosphorus uptake (bioremediation) by seaweed, more CO2 and PO4 equivalents are (temporarily) absorbed than emitted by the supply chain. The extent of emissions is most affected by preservation methods undertaken. Impact profiles of the supply chain show that the greatest impact shares result from freezing and air-cabinet drying, both the two most energy-intensive processes, followed by the cultivation infrastructure, highlighting strategic optimization opportunities. Hatchery processes, harvesting, and the low-energy ensilage and hang-drying outdoors were found to have relatively small impact shares. These findings presage the environmentally friendliness of seaweed-based products by documenting their potential to mitigate eutrophication and climate change, even when taking a life cycle perspective.

The growing world population demands an increase in sustainable resources for biorefining. The opening of new farm grounds and the cultivation of extractive species, such as marine seaweeds, increases worldwide, aiming to provide renewable biomass for food and non-food applications. The potential for European large-scale open ocean farming of the commercial green seaweed crop Ulva is not yet fully realized. Here we conducted manipulative cultivation experiments in order to investigate the effects of hatchery temperature (10 and 15 °C), nutrient addition (PES and 3xPES) and swarmer density (500 and 10,000 swarmers ml−1) on the biomass yield and biochemical composition (fatty acid, protein, carbohydrate, pigment and phenolic content) of off-shore cultivated Ulva fenestrata in a Swedish seafarm. High seedling densities were optimal for the growth of this northern hemisphere crop strain and significantly increased the mean biomass yield by ~84% compared to low seedling densities. Variations of nutrients or changes in temperature levels during the hatchery phase were not necessary to increase the subsequent growth in an open-water seafarm, however effects of the factors on the thallus habitus (thallus length/width) were observed. We found no significant effect of the environmental factors applied in the hatchery on the total fatty acid or crude protein content in the off-shore cultivated Ulva. However, low seedling density and low temperature increased the total carbohydrate content and furthermore, high temperature in combination with high nutrient levels decreased the pigment content (chlorophyll a, b, carotenoids). Low temperature in combination with high nutrient levels increased the phenolic content. Our study confirms the successful and sustainable potential for large-scale off-shore cultivation of the Scandinavian crop U. fenestrata. We conclude that high seedling density in the hatchery is most important for increasing the total biomass yield of sea-farmed U. fenestrata, and that changing temperature or addition of nutrients overall does not have a large effect on the biochemical composition. To summarize, our study contributes novel insights into the large-scale off-shore cultivation potential of northern hemisphere U. fenestrata and underpins suitable pre-treatments during the hatchery phase of seedlings to facilitate a successful and cost-efficient large-scale rope cultivation.

In recent years, the interest in using seaweed for the sustainable production of commodities has been increasing as seaweeds contain many potentially worthwhile compounds. Thus, the extraction and refining processes of interesting compounds from seaweeds is a hot research topic but has been found to have problems with profitability for novel applications. To increase the economic potential of refining seaweed biomass, the content of the compounds of interest should be maximized, which can potentially be achieved through optimization of cultivation conditions. In this study, we studied how the monosaccharide composition of the green seaweed species Ulva fenestrata is influenced by the abiotic factors; irradiance, temperature, nitrate, phosphate, and pCO2. It was evident that lower nitrate concentration and cultivation at elevated temperature increased monosaccharide contents. A 70% increase in iduronic acid and a 26% increase in rhamnose content were seen under elevated irradiance and temperature conditions, though the absolute differences in monosaccharide concentration were small. Irradiance and nitrate impacted the ratio between iduronic and rhamnose, which is an indicator of the ulvan structure. These results could potentially be utilized to coax the ulvan towards specific bioactivities, and thus have a considerable impact on a potential biorefinery centered around Ulva.