Growth, nitrate uptake kinetics, and biofiltration potential of eucheumatoids with different thallus morphologies

Abstract

The declining production of commercially important eucheumatoids related to serious problems, like increasing susceptibility to ice-ice disease and epiphytism, may be ameliorated by nutrition. This ushered an increasing interest in incorporating seaweeds into an integrated multi-trophic aquaculture (IMTA) setup to take up excess inorganic nutrients produced by fish farms for their nourishment. In this regard, it is important to understand the nutrient uptake capacity of candidate seaweeds for incorporation into an IMTA system. Here, we examined the growth, nitrate ( ${\text{NO}}_3^{-}$ ) uptake kinetics, and biofiltration potential of Eucheuma denticulatum and three strains of Kappaphycus alvarezii (G-O2, TR-C16, and SW-13) with distinct thallus morphologies. The ${\text{NO}}_3^{-}$ uptake rates of the samples were determined under a range of ${\text{NO}}_3^{-}$ concentrations (1-48 µM) and uptake rates were fitted to the Michaelis-Menten saturation equation. Among the examined eucheumatoids, only SW-13 had a linear response to ${\text{NO}}_3^{-}$ concentration while other strains had uptake rates that followed the Michaelis-Menten saturation equation. Eucheuma denticulatum had the lowest K_m (9.78 ± 1.48 µM) while G-O2 had the highest V_max (307 ± 79.3 µmol · g^-1 · min^-1 ). The efficiency in ${\text{NO}}_3^{-}$ uptake (highest V_max /K_m and α) was translated into the highest growth rate (3.41 ± 0.58% · d^-1 ) measured in E. denticulatum. Our study provided evidence that eucheumatoids could potentially take up large amount of ${\text{NO}}_3^{-}$ and fix CO₂ when cultivated proximate to a fish farm as one component of an IMTA system. During a 45 -d cultivation period of eucheumatoids, as much as 370 g ${\text{NO}}_3^{-}$ can be sequestered by every 1 kg initial biomass of E. denticulatum growing at 3% · d^-1 . Furthermore, based on our unpublished photosynthetic measurements, the congeneric K. striatus can fix 27.5 g C · kg^-1 DW during a 12 h daylight period.

Keywords: Eucheuma denticulatum; Kappaphycus alvarezii; IMTA; Michaelis-Menten; surface area to volume ratio.