Seasonal variation in productivity, chemical composition and nutrient uptake of Ulva spp. (Chlorophyta) strains

Abstract

Applications of seaweeds require the supply of uniform biomass, yet performance of Ulva is generally characterised by a wide variation across study sites and seasons, as well as among species or strains. This study aimed to determine the variation in growth, biochemical composition and nutrient uptake of five Ulva strains collected in the Eastern Scheldt estuary (the Netherlands) and cultivated under standardised outdoor conditions from July to November. Surprisingly, only two strains performed well (maximum 291 ± 95 and 570 ± 122 kg FW ha−1 day−1 for VEE and YER strain), one strain showed slow growth (maximum 155 ± 91 kg FW ha−1 day−1 for SCH strain), and the last two strains (JAC and KOM) did not grow at all. Chemical composition was only determined for the well-performing strains. For most of the parameters, strong seasonality was observed; growth, crude fat (0.4–1.3%), ash (16–25%) and starch (3–11%) decreased, whereas fibres (37–45%) and proteins (7–22% crude; 6–18% true) increased. To evaluate the bio-remediation potential, nutrient uptake of YER, VEE and SCH strains was determined from in- and outflowing water (453–2027 µmol DIN; 4–101 µmol PO4 kg FW h−1). Highest rates were observed for the SCH strain which was not in accordance with growth nor composition, suggesting that nutrients were not (all) directed towards vegetative growth. This study demonstrates a large variation in performance between different Ulva strains collected in relatively close proximity and thereby highlights the importance to test a variety of local seaweed strains prior to commercial farming.