Bienson Ceasar V. Narvarte1,2, Shienna Mae C. Gonzaga1, Lourie Ann R. Hinaloc1, Tom Gerald T. Genovia1, Michael Y. Roleda1
1The Marine Science Institute, College of Science, University of the Philippines, Diliman 1101, Quezon City, Philippines
In an 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 resultant fecal waste can contribute to variations in nutrient 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 Kappahycus alvarezii, Kappaphycus striatus and Eucheuma denticulatum was examined under laboratory conditions. Samples (n=3) 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 room. Species-specific responses to PO4-3 levels were observed. For K. alvarezii, maximum NH4+ uptake (17.8 ± 1.6 µmol g-1 h-1) was observed at 0.5 µM PO4-3 and the uptake declined at higher PO4-3 levels. For K. striatus, the NH4+ uptake increases with increasing PO4-3 levels, with maximum N-uptake of 6.35 ± 0.9 µmol g-1 h-1 at 5.0 µM PO4-3. For E. denticulatum, maximum NH4+ uptake (14.6 ± 1.4 µmol g-1 h-1) was observed at 1.0 µM PO4-3. Our results have implications on the selection of seaweeds to be incorporated in an IMTA system particularly in mariculture areas where PO4-3 levels significantly vary in space and time.