National Committee on Marine Sciences (NCMS)
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- Comparison of photosynthetic responses of healthy and ‘diseased’ Kappaphycus alvarezii (Doty) Doty using P vs I curveGanzon-Fortes, E. T.; Azanza-Corrales, R.; Aliaza, T. (Walter de Gruyter GmbH, 1993)Healthy and 'diseased' thalli of Kappaphycus alvarezii were collected from two different sites in Bolinao, Pangasinan, northern Philippines. Their photosynthetic responses to varying photon fluence levels we reassessed. The healthy branches had higher photosynthetic rates (expressed in mgO2 gdw"1 h'1) at all light levels and did not show photoinhibition at photon fluence levels of up to 800 μπιοί photons m~2s~!. The 'diseased' branches showed a significant decrease in their photosynthetic performance as manifested by their lower Pmax, increased Ic, and lower alpha, and a photoinhibition above 600 μιηοΐ photons m~2 s"1. Examination of the concentration of pigments — chlorophyll a, r-phycoerythrin and r-phycocyanin, revealed a significant drop in the 'diseased' plants, suggesting the major role played by these pigments in the observed differences in their photosynthetic responses.
- Nutrient limitation of Philippine seagrasses (Cape Bolinao, NW Philippines): in situ experimental evidenceAgawin, N. S. R.; Duarte, C. M.; Fortes, M. D. (Inter-Research Science Center, 1996)Nutrient limitation of Enhalus acoroides, Thalassia hemprichii and Cymodocea rotundata in 2 mixed seagrass beds (Silaqui and Lucero) in Cape Bolinao, NW Philippines was investigated through a 4 mo in situ nutrient addition experiment. Leaf growth of T. hemprichii and E. acoroides significantly increased by 40 to 100% and 160%, respectively, following fertilization. Leaf biomass of the 3 species also increased significantly by 60 to 240% following nutrient additions. The increased growth and biomass with fertilization was supported by enhanced photosynthetic activity, consequently by higher chlorophyll and nutrient concentrations in the photosynthetic tissues. These results demonstrated nutrient limitation of seagrass growth and photosynthetic performance at the 2 sites in Cape Bolinao. The nature and extent of nutrient limitation, however, varied between sites and among species. T. hemprichii and E. acoroides appeared to be mainly P deficient and N deficient, respectively (from significant increases in tissue P and N concentration following fertilization, respectively). The deficiency was moderate (26% of requirement) for T. hemprichii but substantial for E. acoroides (54% of requirement). Moreover, N and P deficiency was greater in Lucero than in Silaqui, consistent with the higher ambient nutrient concentration in the porewater and sediment nutrient and organic matter content in Silaqui. These results emphasize the importance of local differences in the factors controlling nutrient losses and gains in seagrass meadows and, more importantly, the importance of identifying the species-specific traits that generate the interspecific plasticity of nutrient status.
- Diurnal and diel patterns in the photosynthetic performance of the agarophyte Gelidiella acerosaGanzon-Fortes, E. T. (Walter de Gruyter, 1997)Photosynthesis of the red alga Gelidiella acerosa was monitored on diurnal (during the day) and diel (24 h period) bases using the oxygen evolution technique in a closed system. Natural sunlight and artificial light were used to assess uniformity in the diurnal photosynthetic responses. Photosynthesis-irradiance (P-I) curves were also determined diurnally. On a diel basis, maximal photosynthetic rates occurred at day time and minimal rates occurred at night. Diurnally, photosynthesis fluctuated in different patterns depending on PFDs used. Under saturating but not photoinhibiting FFDs, photosynthesis exhibited an early morning minimum (a few hours after sunrise), a midday-noon maximum, sustained until late afternoon, then declined at or after sunset. However, when exposure to high PFDs (above 1200 μιηοΐ photons m"~s") were prolonged, i.e. from morning until afternoon, the photosynthetic performance suffered a depression starting from noon and persisting until afternoon. When PFDs lowered late in the afternoon, recovery of photosynthetic performance commenced resulting in increased photosynthetic rates. The P-I curve data corroborate findings of experiments using saturating but not photoinhibiting PFDs. The morning P-I curve had lower Pm and alpha, and higher Ik and Is values than the identical noon and afternoon P-I curves. This suggested that photosynthetic performance was yet inefficient in the morning but performed efficiently near midday until the afternoon. An endogenous circadian clock was implicated to have influenced the diurnal and diel patterns in the photosynthetic performance of G. acerosa. Photoinhibition was the other factor suspected to have altered the diurnal pattern.
- Metabolic responses of the scleractinian coral Porites cylindrica Dana to water motion. I. Oxygen flux studiesRex, Augustus; Montebon, F.; Yap, Helen T. (Elsevier, 1995-03)Nubbins of Porites cylindrica Dana collected from a shallow reef flat in the northwestern Philippines were studied for water motion effects. Specimens were maintained in field and laboratory high (HWM) and low (LWM) water motion setups. The average maintenance times were 93 and 77 days for the field and laboratory study, respectively, which were carried out in tandem. After each maintenance period, oxygen fluxes of the corals were measured with increasing stirring rates in a laboratory flow-through respirometry system under a constant light intensity. Photosynthesis-irradiance (P-I) curves were also determined for the laboratory maintained nubbins as well as for a set of control nubbins which were kept in the collection site for 71 days. In both HWM and LWM corals, maximum rates of net photosynthesis (NP) and respiration (R) were achieved upon increasing stirring rates or turbulence to a certain level, indicating that the boundary layer limiting oxygen diffusion had been reduced to a minimum. The LWM corals attained maximum photosynthetic rates at lower rates of water motion, suggesting greater photosynthetic efficiency at lower levels of turbulence than their HWM counterparts. Profiles of NP and R with increasing stirring rates were consistently depressed for the LWM corals. Significant differences between the HWM and LWM treatments were detected in the NP profiles of the field maintained corals and in the R profiles of the laboratory maintained nubbins. The small yet significant difference in the NP profiles of the field HWM and LWM corals was attributed to the subsaturating irradiance used in the laboratory measurements because P-I curves of the laboratory maintained corals showed a large and significant difference between water motion treatments (HWM > LWM) at higher irradiances. While exhibiting lower photosynthetic rates, LWM corals had proportionally lower respiration rates resulting in P:R values very close to those of the HWM corals. Results suggest that Porites cylindrica is able to maintain its metabolic efficiency despite changes in the water motion regime.