Abstract
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).
Highlights
Seaweed aquaculture is a growing industry worldwide, which is worth more than 6 billion US$ per year (Buchholz et al 2012; Buschmann et al 2017; FAO 2018)
When data were statistically analysed, we found a significant difference in relative growth rate between algae exposed to different irradiance and temperature levels (Table 1a)
The relative growth rate was on average 14.43% higher at medium and high irradiance compared with low irradiance, and 10.81% higher at low compared with high temperature (Tukey’s HSD, p < 0.05, Fig. 1a, b)
Summary
Seaweed aquaculture is a growing industry worldwide, which is worth more than 6 billion US$ per year (Buchholz et al 2012; Buschmann et al 2017; FAO 2018). J Appl Phycol (2020) 32:3243–3254 genetic differences between species and populations, as well as differences in environmental growth conditions such as temperature, irradiance, salinity, and nutrient composition of the water. Growth generally increases with increasing irradiance, temperature, nutrient, and pCO2 levels The biochemical composition changes with environmental growth conditions, with increasing temperature, nutrients, and pCO2 levels generally increasing total fatty acid and protein content The total phenolic content of Ulva spp. increases with increasing nutrient and temperature levels (Cabello-Pasini et al 2011; Figueroa et al 2014; McCauley et al 2018) and decreasing pCO2 levels (Figueroa et al 2014). From an applied perspective, optimising cultivation conditions to produce high yields of proteins, fatty acids, carbohydrates, and/or bioactive compounds may be more important than optimising growth rate (Hafting et al 2015)
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