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National Committee on Marine Sciences (NCMS)

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AGROVOC Keyword: search.filters.agrovoc.phosphatesOcean Decade Challenge: search.filters.odc.Challenge 2: Protect and restore ecosystems and biodiversity

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    Growth and metabolic responses of the giant clam-zooxanthellae symbiosis in a reef-fertilisation experiment
    Belda-Baillie, C. A.; Leggat, W.; Yellowlees, D. (Inter-Research Science Center, 1998)
    To evaluate the impact of elevated nutrients on reef organisms symbiotic with zooxanthellae, giant clams Tridacna maxima were exposed daily to increased ammonia and phosphate (N, P, N+P) in their natural reef environment for 3 to 6 mo. The results strongly corroborate the major responses of the symbiotic association to nutrient enrichment previously observed (with T. gigas) under controlled outdoor conditions. Exposure of the clams to elevated N (10 µM) increased zooxanthellae density, reduced zooxanthellae size, down-regulated N uptake by zooxanthellae freshly isolated from their hosts, and reduced glutamate in the clam haemolymph, with increased pools of some free amino acids (methionine, tyrosine) in the zooxanthellae. These results confirm that the zooxanthellae in giant clams are N limited in situ and have free access to inorganic N from the sea water. There is also corroborating evidence that the zooxanthellae are P limited in situ as well, possibly due to host interference. While the N:P ratios of the animal host reflected ambient N and P concentrations in the sea water, those of the zooxanthellae did not. Regardless of P exposure (2 µM P) of the clams, zooxanthellae N:P ratios were consistently high(>30:1) and phosphate concentrations in the clam haemolymph bathing the zooxanthellae tube system consistently low (<0.1 µM). These field findings, consistent with previous laboratory observations, confirm the limiting roles of both N and P in the giant clam-zooxanthellae symbiosis. That significant changes occurred earlier and at lower nutrient loading compared to some reef organisms investigated within the same experimental framework further demonstrates organism-level responses of a potential bio-indicator of the early onset of eutrophication in reef waters.
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    Nitrate and phosphate uptake of morphologically distinct calcified macroalgae
    Narvarte, Bienson Ceasar V.; Hinaloc, Lourie Ann R.; Gonzaga, Shienna Mae C.; Crisostomo, Bea A.; Genovia, Tom Gerald T.; Roleda, Michael Y. (Informa UK Limited, 2023-05-02)
    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, Actinotrichia fragilis (Nemaliophycidae) and Amphiroa fragilissima (Corallinophycidae), and the non-geniculate rhodolith Sporolithon sp. (Corallinophycidae) were examined. Sporolithon 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, Sporolithon sp. had the lowest Km (2.72 ± 0.97 µM), Vmax (0.08 ± 0.01 µmol gDW–1 h–1), Vmax/Km (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 A. fragilis had the highest Km (12.35 ± 0.71 µM) and Vmax (6.41 ± 0.23 µmol gDW–1 h–1), and A. fragilissima had the highest Vmax/Km (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.
    This 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.