As the periodic emission of light pulses by light emitting diodes (LEDs) is known to stimulate growth or induce high value biocompounds in microalgae, this flashing light regime was tested on growth and biochemical composition of the microalgae Nannochloropsis gaditana, Koliella antarctica and Tetraselmis chui. At low flashing light frequencies (e.g., 5 and 50 Hz, Duty cycle = 0.05), a strain-dependent growth inhibition and an accumulation of protein, polyunsaturated fatty acids, chlorophyll or carotenoids (lutein, β-carotene, violaxanthin and neoxanthin) was observed. In addition, a 4-day application of low-frequency flashing light to concentrated cultures increased productivities of eicosapentaenoic acid (EPA) and specific carotenoids up to three-fold compared to continuous or high frequency flashing light (500 Hz, Duty cycle = 0.05). Therefore, applying low-frequency flashing light as finishing step in industrial production can increase protein, polyunsaturated fatty acids or pigment contents in biomass, leading to high-value algal products.

Main Conclusion: The combined photoinhibitory and PSII-reaction centre quenching against light stress is an important mechanism that allows the green macroalga Ulva rigida to proliferate and form green tides in coastal ecosystems. Eutrophication of coastal ecosystems often stimulates massive and uncontrolled growth of green macroalgae, causing serious ecological problems. These green tides are frequently exposed to light intensities that can reduce their growth via the production of reactive oxygen species (ROS). To understand the physiological and biochemical mechanisms leading to the formation and maintenance of green tides, the interaction between inorganic nitrogen (N_i) and light was studied. In a bi-factorial physiological experiment simulating eutrophication under different light levels, the bloom-forming green macroalga Ulva rigida was exposed to a combination of ecologically relevant nitrate concentrations (3.8–44.7 µM) and light intensities (50–1100 µmol photons m⁻² s⁻¹) over three days. Although artificial eutrophication (≥ 21.7 µM) stimulated nitrate reductase activity, which regulated both nitrate uptake and vacuolar storage by a feedback mechanism, nitrogen assimilation remained constant. Growth was solely controlled by the light intensity because U. rigida was N_i-replete under oligotrophic conditions (3.8 µM), which requires an effective photoprotective mechanism. Fast declining Fv/Fm and non-photochemical quenching (NPQ) under excess light indicate that the combined photoinhibitory and PSII-reaction centre quenching avoided ROS production effectively. Thus, these mechanisms seem to be key to maintaining high photosynthetic activities and growth rates without producing ROS. Nevertheless, these photoprotective mechanisms allowed U. rigida to thrive under the contrasting experimental conditions with high daily growth rates (12–20%). This study helps understand the physiological mechanisms facilitating the formation and persistence of ecologically problematic green tides in coastal areas.

During the cultivation of Ulva fenestrata in a land-based aquaculture system, the colonisation of the water tanks’ surfaces and eventually the macroalgal biomass by the biofouling diatom Fragilariopsis oceanica compromises the production process. Since germanium dioxide (GeO₂) is an effective growth inhibitor of diatoms, this study aimed to understand how it affects the presence of F. oceanica and the photosynthesis and growth of U. fenestrata as a primary parameter contribution to the biomass production. A toxicological dose-response experiment showed that the diatom’s growth was inhibited at the low GeO₂ concentration of 0.014 mg l⁻¹. In contrast, the photosynthetic performances and growth rates of U. fenestrata remained unaffected under a wide GeO₂ concentration range (0.022–2.235 mg l⁻¹) in small- and large-scale experiments in 1-l glass beakers and 100-l Plexiglass water tanks, respectively. In the latter, the diatom density in the tanks was reduced by 40 %. The costs arising from the use of GeO₂ can range between €2.35 and €8.35 kg⁻¹ fresh weight of produced U. fenestrata biomass under growth conditions resulting in growth rates of 20 and 11.5 % d⁻¹, respectively. GeO₂ is an effective agent to control biofouling diatoms such as F. oceanica during the land-based biomass production of U. fenestrata.

Aim: This study sets out to understand the variability in larval traits of dispersive life stages of a famous invader, the European shore crab Carcinus maenas , in its native distribution range. Location: North East Atlantic coast from the Norwegian Arctic to the southern European distribution limit of C. maenas in Southern Spain. Taxon: European shore crab Carcinus maenas (Crustacea, Decapoda). Methods: We quantified latitudinal patterns in larval body mass, elemental composition (C and N content), and thermal tolerance of the first larval stage. We collected crabs from four populations spanning 25° of latitude (Vigo in Northern Spain; Bergen, Trondheim, and Bodø in Norway) and reanalysed published and unpublished data of body mass and elemental composition of additional populations from Germany, Wales, France, and Southern Spain. Furthermore, we used two laboratory experiments to test the thermal tolerance limits of the first larval stage from Vigo and the Norwegian populations. In the first experiment, we reared larvae from hatching to Zoea II at seven temperatures (9°C–27°C) and from hatching to LT ₅₀ at 6°C. In the second experiment, we exposed freshly hatched larvae acutely to increasing or decreasing temperatures (up to 40°C and down to 3°C). Results: Across the entire European range, we found a substantial increase in dry mass and carbon and nitrogen content of freshly hatched larvae with latitude. Norwegian populations exhibited higher survival at 9°C than the Vigo population. Furthermore, LT ₅₀ at 6°C increased from South to North. All populations showed high survival in the range 12°C–24°C but low survival at 27°C. Main Conclusions: Larval tolerance quantified by using survival to Zoea II is not clearly related to the tolerance quantified with the acute experiments, indicating that each method assesses different aspects of thermal tolerance. Tolerance to low temperature correlated positively to tolerance to high temperature, suggesting that variation among females in larval responses reflects a general physiological quality rather than trade‐offs. We provide evidence for potentially adaptive variations in larval body mass and thermal tolerance across a latitudinal gradient for C. maenas .

The brown marine macroalga Alaria esculenta contains phlorotannins as polyphenolic compounds in its cell walls. This study aimed to understand their antioxidant effects on preserving the lipids in fillets of freshly-slaughtered farmed Atlantic salmon (Salmo salar). First, soluble phlorotannins were extracted from wild-grown population of A. esculenta in North Norway (Bodø) using solid/liquid extraction. A small-scale solid/liquid extraction (15 mg mL⁻¹) with 70% acetone showed that 84% of total soluble phlorotannins (25.10 mg g⁻¹ dry weight) were extracted after the first out of four extraction steps. In a large-scale extraction (3 mg 400 mL⁻¹), the contents of soluble phlorotannins and the DPPH-based antioxidant capacities (measured as IC₅₀) in 70% acetone- and water-based crude extracts were similar. Water is preferred extraction solvent for the following experiment because it complies with food safety standards, may minimise work procedures and is in accordance with the principles of Green Chemistry. Secondly, the antioxidant properties of the soluble phlorotannins were tested through incubating salmon fillets (Norwegian Quality Cuts) in water-based extracts. After six days of storage on ice, the peroxide value of Alaria-treated fillets was lower compared to the control (without Alaria-extract), while the p-anisidine and free fatty acid values remained unchanged. This indicates the phlorotannins’ inhibitory effect on the formation of primary rather than secondary lipid oxidation products. This study demonstrated that the antioxidant properties of the soluble phlorotannins extracted from A. esculenta using water can preserve the nutritional value of salmon fillets to extend the seafood’s shelf-life.