Exploring the suitable extractive species in an IMTA: inorganic nutrient removal from mariculture effluents by commercially important marine macroalgae

Abstract The ability of macroalgae to extract inorganic nutrients is crucial in selecting species for integrated multitrophic aquaculture (IMTA). This study assessed the nutrient removal capacities of five commercially important marine macroalgae – Caulerpa microphysa , Ulva ohnoi , Kappaphycus alvarezii , Kappaphycus striatus , and Eucheuma denticulatum – using eutrophic seawater from a mariculture farm. All species simultaneously took up three inorganic nitrogen species (NH 4 + , NO 3 − and NO 2 − ), with a strong preference for NH 4 + (11.8–24.5 µmol gDW −1 h −1 ) over NO 3 − (0.04–2.31 µmol gDW −1 h −1 ) and NO 2 − (0.02–0.38 µmol gDW −1 h −1 ). Specifically, C. microphysa had the highest PO 4 3− uptake (0.43 ± 0.04 µmol gDW −1 h −1 ), while K. alvarezii had the highest NH 4 + uptake (20.6 ± 0.68 µmol gDW −1 h −1 ) and U. ohnoi showed the highest NO 3 − (1.92 ± 0.25 µmol gDW −1 h −1 ) and NO 2 − (0.30 ± 0.04 µmol gDW −1 h −1 ) uptake rates. Principal component analysis grouped species by uptake rates, and projections indicated that U. ohnoi and K. alvarezii would have absorbed the most nitrogen and phosphorus, respectively, over 45 days. These findings highlight the potential of these macroalgae as extractive species in IMTA, reducing eutrophication risks and promoting sustainable aquaculture.