2. Materials and methods
2.1. Algal culture
Gracilaria cornea J. Agardh, Hypnea spinella (C. Agardh) Kützing and Hypnea musciformis (Wulfen) J. V. Lamoroux were grown in a flow-through integrated system consisting of two intensive fishponds stocked with gilthead sea bream and a macroalgal biofilter. Effluents were channelled from the fishponds to a 11 m3 sedimentation pond for the removal of suspended particles and, then, pumped at a flow rate of 10 m3 h−1 to the seaweed tanks located in a greenhouse, where maximum irradiance was close to 1600 μmol photons m−2 s−1. Semi-circular fiberglass tanks with a surface of 1.8 m2, volume of 0.75 m3 and aeration supplied by a bottom-central linear pipeline were used for the cultivation of macroalgae. Algal stocking densities were adjusted to the optimal values obtained from previous experiments (6 g l−1). Water exchange rate in the seaweed tanks was 4 vol day−1 and TAN (total ammonia nitrogen) inflow into the biofilter ranged between 10 and 400 μM.