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

Sea lettuce (Ulva) aquaculture has increased the last decade due to high productivity, wide environmental tolerance, and interesting functional and nutritional properties of the crop. Research focus has mainly been on adult biomass production, but knowledge of performance and biochemical content of early developmental stages – which are the basis to any large-scale production - is still limited. The life-history of Ulva alternates between a diploid sporophytic life-stage and a haplontic gametophytic life-stage. Whereas the sporophyte give raise to recombinant gametophytes through zoids, gametophytes can give raise to parthenogenetically developing, clonal gametes in absence of a mating partner. This study shows that recombinant gametophytes have a faster ontogenetic development, higher growth rate, as well as higher protein, fatty acid, and pigment contents compared to clonal gametophytes of the crop Ulva fenestrata. Nutrient addition is required for a normal development, but temperature and swarmer density have relatively small effects on the hatchery success, relative growth rate and biochemical profile of the juvenile biomass. Our study reveals that the selection of the life-history-phase in novel sea lettuce crop strains could largely contribute to the emerging seaweed aquaculture sector

Designing Equitable Transit Networks

Public transit is an essential infrastructure enabling access to employment, healthcare, education, and recreational facilities. While accessibility to transit is important in general, some sections of the population depend critically on transit. However, existing public transit is often not designed equitably, and often, equity is only considered as an additional objective post hoc, which hampers systemic changes. We present a formulation for transit network design that considers different notions of equity and welfare explicitly. We study the interaction between network design and various concepts of equity and present trade-offs and results based on real-world data from a large metropolitan area in the United States of America.Comment: Accepted in the non-archival track at the ACM Conference on Equity and Access in Algorithms, Mechanisms, and Optimization (EAAMO), 202

Cultivation of seaweeds in food production process waters: Evaluation of growth and crude protein content

There is an increasing demand for sustainably produced, protein-rich, and nutritious food. Seaweeds are promising protein sources for the future if their protein content can be optimized, something which can be achieved by cultivation in elevated nutrient concentrations. Cultivation of seaweeds in integration with fish farms have received much attention lately, but using nutrient-rich process waters from other food industries as feed stock for seaweed has rarely been studied. Here, we demonstrate a simple and sustainable strategy to answer the increasing world demand for food rich in plant-based proteins by connecting food production process waters with seaweed cultivation. We compared growth rates and crude protein content of four different seaweed species, the brown species Saccharina latissima, and the green species Ulva fenestrata, Ulva intestinalis, and Chaetomorpha linum, when cultivated in two dilutions (providing 20 and 200 μM ammonium) of eight different process waters emerging from recirculating salmon aquaculture systems as well as from herring, shrimp and oat processing. Growth rates of the green seaweeds were up to 64% higher, and crude protein content was almost up to four times higher when cultivated in the food production process waters, compared to seawater controls. Growth rates were generally higher in presence of 20 μM compared to 200 μM ammonium, while crude protein content was either unaffected or positively affected by the increasing ammonium concentration. This study indicates the potential for cultivating seaweeds with food production process waters to generate additional protein-rich biomass while nutrients are being circulated back to the food chain. A new nutrient loop is thus illustrated, in which the costly disposal of food production process waters is instead turned into value by seaweed cultivation

Post-harvest cultivation with seafood process waters improves protein levels of Ulva fenestrata while retaining important food sensory attributes

Seaweed aquaculture can provide the growing human population with a sustainable source of proteins. Sea-based cultivation is an effective method for farming seaweeds on a large scale and can yield high biomass output. However, the quality and biochemical composition of the biomass is seasonally dependent, which limits the harvests to certain periods of the year. Here we show the possibility to extend the sea-based cultivation season of Ulva fenestrata when aiming for high protein levels, by post-harvest treatment in herring production process waters. We harvested U. fenestrata at an optimal period in terms of yield, but suboptimal in terms of protein content. We then cultivated the seaweed in onshore tank systems with the nutrient-rich process waters for 14 days. We monitored biomass yield, crude protein content, amino acid composition, and content of the health concerning metals arsenic, mercury, lead, and cadmium, as well as the sensory properties of the dried biomass. After cultivation in the process waters, biomass yields were 30 - 40% higher (210 – 230 g fresh weight) compared to in seawater (160 g fresh weight). Also, the crude protein and amino acid content increased three to five times in the process waters, reaching 12 - 17 and 15 – 21% dry weight, respectively. The protein enriched biomass followed food graded standards for heavy metal content, and consumption of the biomass does not exceed health based reference points. Additionally, no sensory attributes regarded as negative were found. This rapid, post-harvest treatment can help extend the cultivation season of sea-based seaweed farms, maximizing their output of sustainable proteins

Sustainable large-scale aquaculture of the northern hemisphere sea lettuce, ulva fenestrata, in an off-shore seafarm

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 vitro digestibility and Caco-2 cell bioavailability of sea lettuce (Ulva fenestrata) proteins extracted using pH-shift processing

Seaweed is a promising sustainable source of vegan protein as its farming does not require arable land, pesticides/insecticides, nor freshwater supply. However, to be explored as a novel protein source the content and nutritional quality of protein in seaweed need to be improved. We assessed the influence of pH-shift processing on protein degree of hydrolysis (%DH), protein/peptide size distribution, accessibility, and cell bioavailability of Ulva fenestrata proteins after in vitro gastrointestinal digestion. pH-shift processing of Ulva, which concentrated its proteins 3.5-times, significantly improved the %DH from 27.7\ub12.6% to 35.7\ub12.1% and the amino acid accessibility from 56.9\ub14.1% to 72.7\ub10.6%. Due to the higher amino acid accessibility, the amount of most amino acids transported across the cell monolayers was higher in the protein extracts. Regarding bioavailability, both Ulva and protein extracts were as bioavailable as casein. The protein/peptide molecular size distribution after digestion did not disclose a clear association with bioavailability

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

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

Effects of irradiance, temperature, nutrients, and pCO2 on the growth and biochemical composition of cultivated Ulva fenestrata

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\ua0μmol photons m−2\ua0s−1), temperature (13 and 18\ua0\ub0C), nitrate (< 5, 150, and 500\ua0μM), phosphate (< 1 and 50\ua0μM), and pCO2 (200, 400, and 2500\ua0ppm) 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)

Cultivation conditions affect the monosaccharide composition in Ulva fenestrata

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.\ua0\ua9 2020, The Author(s)

Salinity and host drive Ulva ‐associated bacterial communities across the Atlantic–Baltic Sea gradient

The green seaweed Ulva is a model system to study seaweed–bacteria interactions, but the impact of environmental drivers on the dynamics of these interactions is little understood. In this study, we investigated the stability and variability of the seaweed-associated bacteria across the Atlantic–Baltic Sea salinity gradient. We characterized the bacterial communities of 15 Ulva sensu lato species along 2,000 km of coastline in a total of 481 samples. Our results demonstrate that the Ulva-associated bacterial composition was strongly structured by both salinity and host species (together explaining between 34% and 91% of the variation in the abundance of the different bacterial genera). The largest shift in the bacterial consortia coincided with the horohalinicum (5–8 PSU, known as the transition zone from freshwater to marine conditions). Low-salinity communities especially contained high relative abundances of Luteolibacter, Cyanobium, Pirellula, Lacihabitans and an uncultured Spirosomaceae, whereas high-salinity communities were predominantly enriched in Litorimonas, Leucothrix, Sulfurovum, Algibacter and Dokdonia. We identified a small taxonomic core community (consisting of Paracoccus, Sulfitobacter and an uncultured Rhodobacteraceae), which together contributed to 14% of the reads per sample, on average. Additional core taxa followed a gradient model, as more core taxa were shared between neighbouring salinity ranges than between ranges at opposite ends of the Atlantic–Baltic Sea gradient. Our results contradict earlier statements that Ulva-associated bacterial communities are taxonomically highly variable across individuals and largely stochastically defined. Characteristic bacterial communities associated with distinct salinity regions may therefore facilitate the host's adaptation across the environmental gradient