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 (NO3‐) 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 NO3‐ uptake rates of the samples were determined under a range of NO3‐ 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 NO3‐ concentration while other strains had uptake rates that followed the Michaelis–Menten saturation equation. Eucheuma denticulatum had the lowest Km (9.78 ± 1.48 µM) while G‐O2 had the highest Vmax (307 ± 79.3 µmol · g−1 · min−1). The efficiency in NO3‐ uptake (highest Vmax/Km 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 NO3‐ 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 NO3‐ 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 Furthermore, based on our unpublished photosynthetic measurements, the congeneric K. striatus can fix 27.5  g C · kg−1 DW during a 12 h daylight period.

No abstract

No abstract

In an integrated multitrophic aquaculture (IMTA) system, seaweeds serve as extractive species that utilize excess nutrients thereby reducing the risk of eutrophication and promoting sustainable aquaculture. However, the use of excessive fish feeds and the resultant fecal waste as nutrient streams can contribute to variations in nitrogen and phosphorus levels (e.g., primarily NH4+ and PO4-3) in the surrounding area, and this may impact the physiology of the integrated seaweeds particularly on how these species take up inorganic nutrients. In this study, the effect of different PO4-3 levels on NH4+ uptake of the three commercially important eucheumatoids Kappaphycus alvarezii, Kappaphycus striatus and Eucheuma denticulatum was examined under laboratory conditions. Seaweed thalli (n = 4) were incubated in seawater media containing 30 µM NH4+, representing eutrophic conditions, and 0, 0.5, 1.0, 1.5, 3.0 or 5.0 µM PO4-3 for 1 h under a saturating light level of 116 ± 7.13 µmol photons m-2 s-1 inside a temperature-controlled laboratory. Species-specific responses to PO4-3 levels were observed. For K. alvarezii, maximum NH4+ uptake (17.8 ± 1.6 µmol gDW-1 h-1) was observed at 0.5 µM PO4-3 and the uptake rate declined at higher PO4-3 levels. For K. striatus, the NH4+ uptake increases with increasing PO4-3 levels, with maximum N-uptake (6.35 ± 0.9 µmol gDW-1 h-1) observed at 5.0 µM PO4-3. For E. denticulatum, maximum NH4+ uptake (14.6 ± 1.4 µmol gDW-1 h-1) was observed at 1.0 µM PO4-3. Our results suggest that, among the three eucheumatoid species, the NH4+ uptake of K. striatus persist even at high levels of PO4-3. However, our results also showed that K. striatus had the lowest range of NH4+ uptake rates. These results should be taken into consideration when incorporating eucheumatoids in IMTA system where PO4-3 levels significantly vary in space and time.

No abstract