On the bioremediation efficiency of Mastocarpus stellatus (Stackhouse) Guiry, in an integrated multi-trophic aquaculture system

The potential of rearing the red seaweed Mastocarpus stellatus (Stackhouse) Guiry, a carrageenophyte, as a biofilter in a pilot-scale, integrated multi-trophic aquaculture (IMTA) system was investigated. From April to June, M. stellatus, collected from a population in the north of Portugal was cultivated in 1200-L tanks in two consecutive, 4-week experiments with nutrient-enriched waters derived from fish tanks. The stocking density of 3 kg m(-2) provided the best yields, ranging from 29.6 g dw m(-2) day(-1) in April-May to 38.9 g dw m(-2) day(-1) in June. In the April-May period, a linear increase in the yields was found at higher densities. M. stellatus growth rates during April-May period did not diverge significantly between stocking densities and reached a mean relative growth rate of 3.09 +/- 0.90 % day(-1) in April-May and 4.02 +/- 0.43 % day(-1) in June at 3 kg m(-2). In June, the increase in stocking density negatively affected the growth rates (3 < 2 < 1 kg m(-2)). M. stellatus used ammonium (TAN) as the main N source and the nutrient uptake efficiency was found to be similar between stocking densities, but highest in June. The seaweeds removed an average of 66.29 +/- 3.57 mu mol TAN L-1 in May and 84.49 +/- 4.00 mu mol TAN L-1 in June, which corresponded to the mitigation of 43.19 +/- 1.61 and 49.00 +/- 1.59 % of NH3 from the system, respectively. This study demonstrated the potential to effectively cultivate M. stellatus in an IMTA system.