Combine effects of multiple environmental factors on growth and nutrient uptake of euryhaline seaweed growth in integrated multitrophic aquaculture systems

Abstract

Macroalgae are biofilters that increase the ability of the environment to assimilate nutrients and whose biomass finds different uses in the industrial sector. The growth of Ulva sp. and Gracilaria lemaneiformis and their ability to remove nutrients from enriched water was assessed in a series of laboratory experiments. This study tested their growth performance under: a) three different salinities (15, 20 and 25 psu), b) three different initial densities (low(1 g/l), medium (2 g/l) and high(3 g/l)) and c) four light intensities (1000, 2000, 3000 and 4000 lx). The best results regarding the specific growth rate were achieved for Ulva and Gracilaria (SGR 11 % and 6 %) under light intensity of 3000 lx, salinity of 25 psu, and density of 2 g/l. After four days >80 % of NH4-N and 95 % of PO4-P had been removed from the tanks by Ulva sp. The growth and production performance were tested among: 1) three different depths (10, 20 and 30 cm) in multitrophic system (Fishes + Macroalgae). Finally, based on the best combination obtained from the first phase of the experiment, it was set up the last experiment where the nutrient uptake performances of Ulva were tested among three multitrophic systems (IMTA (Fishes +mussel + Ulva), “Fishes + Ulva”, “Fishes + mussel”). Although the best cultivation depth was 10 cm for both Ulva and Gracilaria, there were significant differences between the WBP (Wet Biomass Production) of the two species (Ulva WBP =46 ± 8.02 g m−2d−1; Gracilaria WBP = 8.5 ± 0.51 g m−2d−1) (p < 0.05). Finally, after the 8th-day experiments, the concentrations of NH4–N were lower in the “Fishes+Ulva” (44.32 %) system and IMTA (27.36 %) system compared with the “Fishes+mussel” system. Moreover, phosphates (PO4-P) concentration decreased by 51.75 % and 57.58 % in the aquaria with “Fishes+Ulva” system and IMTA system, respectively. The results obtained in this study show that Ulva sp. and G. lemaneiformis can grow satisfactorily and absorb nutrients from water efficiently, proving to be suitable candidates for wastewater treatment of aquaculture facilities.