Narvarte, Bienson Ceasar V.Hinaloc, Lourie Ann R.Gonzaga, Shienna Mae C.Crisostomo, Bea A.Genovia, Tom Gerald T.Roleda, Michael Y.2025-03-232023-05-02Narvarte, B. C. V., Hinaloc, L. A. R., Gonzaga, S. M. C., Crisostomo, B. A., Genovia, T. G. T., & Roleda, M. Y. (2023). Nitrate and phosphate uptake of morphologically distinct calcified macroalgae. Phycologia, 62(6), 551-560.0031-88842330-296810.1080/00318884.2023.2197636https://repository.unesco.gov.ph/handle/123456789/185This is contribution no. 494 from the University of the Philippines – the Marine Science Institute, (UP-MSI). We thank our laboratory aides Jerry Arboleda, Guillermo Valenzuela and Robert Valenzuela for their help in our sample collection. We also thank the UPMSI-Bolinao Marine Laboratory for providing us with the venue where we conducted our experiment and laboratory analyses. MYR acknowledges the Department of Science and Technology (DOST) Balik Scientist Program (BSP) fellowship.Calcified macroalgae are essential components of marine ecosystem, yet much of their physiology remains to be understood. Here, the nutrient (NO₃^– and PO₄^–3) uptake physiologies of two branched macroalgae, <i>Actinotrichia fragilis</i> (Nemaliophycidae) and <i>Amphiroa fragilissima</i> (Corallinophycidae), and the non-geniculate rhodolith <i>Sporolithon</i> sp. (Corallinophycidae) were examined. <i>Sporolithon</i> sp. had the lowest uptake rate through time and the three calcified macroalgae had a surge in NO₃^– and PO₄^–3 uptake that occurred between 3 and 20 min, with a maximum uptake at 3 min, after which the nutrient uptake rates declined. The NO₃^– uptake of the three calcified macroalgae followed Michaelis-Menten kinetics. For NO₃^– uptake, <i>Sporolithon</i> sp. had the lowest K_m (2.72 ± 0.97 µM), V_max (0.08 ± 0.01 µmol gDW^–1 h^–1), V_max/K_m (0.05 ± 0.03 µmol gDW^–1 h^–1 µM⁻¹) and α (0.01 ± 0.00 µmol gDW^–1 h^–1 µM⁻¹), while <i>A. fragilis</i> had the highest K_m (12.35 ± 0.71 µM) and V_max (6.41 ± 0.23 µmol gDW^–1 h^–1), and <i>A. fragilissima</i> had the highest V_max/K_m (1.52 ± 0.26 µmol gDW^–1 h–1 µM⁻¹) and α (0.37 ± 0.01 µmol gDW^–1 h^–1 µM⁻¹). Moreover, the PO₄^–3 uptake rate of the three species was faster at higher PO₄^–3 levels. These differences in species-specific nutrient uptake traits are likely caused by differences in morphology. These traits are important for survival and proliferation of this group of marine organisms, particularly in a nutrient-variable environment.enNitratesPhosphatesMorphologyAlgaeMarine algaeNitrogen cycleArticleSDG 14 - Life below waternitratesphosphatesmorphologyAlgaenutrient uptakenutrient availabilityphysiological processesnutrient cyclesmarine ecosystemsChallenge 2: Protect and restore ecosystems and biodiversity