Ammonium and nitrate uptake by Laminaria saccharina and Nereocystis luetkeana originating from a salmon sea cage farm

In the laboratory, ammonium and nitrate uptakes were measured for juvenile Laminaria saccharina (L.) Lamour. and Nereocystis luetkeana (Mert.) Post. et Rupr. originating from a salmon sea cage farm in northwestern British Columbia, Canada. The effect of various concentrations of NH4+ and NO3-, which are typical of salmon farming environments, on uptakes values were examined. Both. L. saccharina and Nereocystis revealed simultaneous uptake of NH4+ and NO3- when both NH4+ and NO3- were present in the medium. During a 3-h incubation, mean uptake rates of NH4+ and NO3- by L. saccharina ranged from 6.0-8.9 and 4.6-10.6 mu mol g(dw)(-1) h(-1), respectively, and by Nereocystis, they ranged from 6.6-9.3 mu mol g(dw)(-1) h(-1) and 6.1-17.0 mu mol g(dw)(-1) h(-1), respectively. The highest uptake rates (14.8 mu mol NH4+ g(dw)(-1) h(-1) by L. saccharina and 27.2 mu mol NO3- g(dw)(-1) h(-1) by Nereocystis) occurred at the highest concentration (40 mu M NH4+ plus 30 mu M NO3-) during a 1 h incubation. Nitrate uptake by both L. saccharina and Nereocystis increased linearly up to the highest nitrate level tested (30 mu M), whereas uptake rates of ammonium were stable beyond 10 mu M NH4+ to reach approximately 10 and 13 mu mol g(dw)(-1) h(-1) respectively, for L. saccharina and Nereocystis. Unlike L. saccharina, Nereocystis showed a significant preference for NO3- when more than 20 mu M NO3- was present in the medium (p < 0.05). Both L. saccharina and Nereocystis would be suitable for integrated cultivation of salmon/kelp.