Biofiltering efficiency and productive performance of macroalgae with potential for integrated multi-trophic Aquaculture (IMTA)

Abstract

Seaweeds have many uses in industry and agriculture and many species have potential for integrated multi-trophic aquaculture (IMTA), since they are efficient in removing nutrients from water. The efficiency of Ulva flexuosa, U. fasciata and Gracilaria birdiae in removing nutrients from enriched water and their productive performance in outdoor tanks were quantified. These seaweeds (50 g; n = 5) were grown in tanks containing 50 L of eutrophic seawater, with a salinity of 30, a temperature of 28.5 ± 2.8 °C, an irradiance of 547 ± 458 μmol photons m-2 s-1 and aeration. The nutrients levels were recorded daily and when total nitrogen removal was detected, the biomass was measured. After five days of cultivation, more than 98% of NH3 (H = 1.1; P = 0.56) and NO3- (H = 2.7; P = 0.25) and 62.1% of PO43- (H = 0.0; P = 0.90) had been removed from the tanks. However, the mean daily growth rate (4.5 ± 2.5% day-1) and productivity (3.5 ± 1.9 g m-2 day-1) of U. fasciata and G. birdiae were higher than U. flexuosa (-13.6 ± 7.7% day-1; -6.24 ± 2.8 g m-2 day-1; P<0.01), demonstrating that microalga contamination by this species promoted high removal efficiency in the tanks, but a low productive performance. Based on these results, U. fasciata and G. birdiae show a greater potential for use in IMTA to improve water quality and produce biomass.