The variations in culture conditions (irradiance, temperature, pH and dissolved oxygen) in a thin-layer 120 m 2 surface reactor have been studied, both in terms of position inside the reactor and time of the daylight cycle. Results demonstrate that average irradiance and temperature to which the cells are exposed are mainly a function of time, whereas pH and dissolved oxygen concentrations also showed relevant gradients depending on their position inside the reactor. The existence of gradients has been demonstrated to reduce the culture performance, using both chlorophyll-fluorescence and net photosynthesis rate methods. Moreover, the influence of culture conditions on Scenedesmus almeriensis cell performance was modelled. The obtained model allows us to quantify the loss in productivity caused by inadequate culture conditions; the net photosynthesis rate being demonstrated as only 32% of the maximal achievable. This is the first step in optimizing and scaling-up this type of reactor for industrial applications.

The improvement of photosynthetic efficiency in a 100 m 2 raceway reactor by enhancement of light regime to which the cells are exposed is here reported. From Computational Fluid Dynamics it was calculated that the light exposure times ranged from 0.4 to 3.6 s while the exposure times to darkness were much longer, from 6 to 21 s. It was demonstrated that these times are too long for light integration, the cells fully adapting to local irradiances. This phenomenon was validated in the real outdoor raceway at different seasons. Simulations allows to confirm that if total light integration is achieved biomass productivity can increase up to 40 g/m 2 •day compared to 29 g/ m 2 •day obtained considering local adaptation, which is close to the experimental value of 25 g/m 2 •day. This paper provides clear evidence of microalgae cell adaptation to local irradiance because of the unfavourable cell movement pattern in raceway reactors.

This study evaluates the production of biomass and mycosporine-like amino acids (MAAs) throughout the year in Gracilaria vermiculophylla (Rhodophyta) collected in Ria de Aveiro (Portugal). The algae were grown in outdoor tanks in seawater with the addition of fishpond effluents under two different water flows (100 and 200 L h) in an integrated multi-trophic aquaculture (IMTA) system (tanks 1200 L; 1.5 m) and different algal densities (3, 5, and 7 kg m). MAA content in IMTA seaweeds was significantly affected by the interaction of time and stocking density, but not by the water flow. The highest MAA content was observed in April (about 3.13 mg g DW) followed by May (1.79 mg g DW). Seaweed biomass productivity was higher in May (372.06 g DW m week) than in April (353.40 g DW m week). Four MAAs were identified by HPLC and electrospray ionization mass spectrometry (ESI-MS) in G. vermiculophylla: Porphyra-334, Shinorine, Palythine and Asterina-330. The highest levels of Porphyra-334 and Shinorine were reached from November to January and the Palythine + Asterina-330 from April to August. Taking into account the average biomass and MAA production of G. vermiculophylla growing in this IMTA system (8.56 g of MAA in 18 m culture along 8 months; 35.5% produced in April), a total amount of 71.33 g MAA year could be produced in this system by scaling up to 100 m. MAAs could be further used as photoprotector and antioxidant compounds in cosmetic products.

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