Seasonal ammonium uptake kinetics of four brown macroalgae: Implications for use in integrated multi-trophic aquaculture

Abstract

AbstractThe combined culture of fed species (bivalves, fish) and macroalgae, known as integrated multi-trophic aquaculture (IMTA), has been suggested as a method of mitigating localised nitrogen (N) increase from aquaculture, whilst simultaneously culturing macroalgae for commercial applications. The development of IMTA requires an understanding of the N ecophysiology of candidate macroalga species. We examined seasonal variations in ammonium (NH4+) uptake kinetics, carbon to nitrogen (C:N) ratio, pigment content and soluble tissue N of four macroalgae of the phylum Ochrophyta, Ecklonia radiata, Macrocystis pyrifera, Lessonia corrugata, and Phyllospora comosa, from Tasmania, Australia. This study aimed to determine, (1) if the N physiology of the four macroalgal species was suitable for IMTA applications and (2) whether the species had seasonal variations in N ecophysiology which would influence their suitability for IMTA. Macrocystis pyrifera, L. corrugata, and E. radiata exhibited saturable NH4+ uptake kinetics, with a maximum uptake rate (Vmax) during spring, summer and autumn of 200, 45.8 and 45 μmol gDW-1 h-1 and half-saturation constants (Ks) of 361.3, 104.2 and 121 μM, respectively. Phyllospora comosa exhibited biphasic uptake patterns for three out of four months sampled. There were no noticeable seasonal patterns in pigment content or soluble tissue N for any species. C:N ratios increased from spring (October) to autumn (March) in both E. radiata (28.34 – 47.83) and P. comosa (24.99 – 51.62), indicating progressive N limitation though summer and into autumn. Results suggest that M. pyrifera and P. comosa are most suitable for IMTA due to their high NH4+ uptake potential.