National Committee on Marine Sciences (NCMS)
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- Ammonium and phosphate excretion in three common echinoderms from Philippine coral reefsDy, Danilo T.; Yap, Helen T. (Elsevier BV, 2000-08)The ammonium and phosphate excretion and oxygen consumption of three species of echinoderms (Tripneustes gratilla, Protoreaster nodosus and Ophiorachna incrassata) commonly encountered in Philippine coral reefs were investigated in relation to time of day (i.e. daytime between 10:00 and 12:00 h vs. nighttime between 22:00 and 24:00 h) and their recent feeding history (i.e. recently-collected vs. short-term starvation for 3±1 days). The experiment used whole organism incubations and followed a nested hierarchical design. Ammonium excretion rates were 1447±310 nmol g−1 DW h−1 (mean±S.E., n=24) for T. gratilla, 361±33 for O. incrassata and 492±38 for P. nodosus. Ammonium excretion differed significantly among species, time of incubation and recent feeding history. Interaction between species and recent feeding history was also significant. The organisms excreted more ammonium during daytime except for starved specimens of O. incrassata. In addition, animals that were starved in the laboratory for a few days had a tendency to excrete more ammonium than recently-collected specimens. Phosphate excretion rates were 25±13 nmol g−1 DW h−1 for T. gratilla, 10±2 for O. incrassata and 4±1 for P. nodosus. There were no significant differences in phosphate excretion among the three species of echinoderms, their recent feeding history and time of day. Oxygen consumption rates were 286±24 μg O2 g−1 DW h−1 for T. gratilla, 64±3 for O. incrassata and 54±3 for P. nodosus. Oxygen consumption differed significantly among species and recent feeding history but differed only slightly with time of incubation. There was a significant correlation between oxygen consumption and ammonium excretion (r=0.48, P=0.018), and between oxygen consumption and phosphate excretion (r=0.41, P=0.047) for T. gratilla. The nutrient excretion by tropical echinoderms is another pathway by which inorganic nutrients are regenerated in coral reef communities. However, the quantity of nutrients excreted is dependent on the species of echinoderms, their nutritional status and time of day.
- Macroinfaunal biomass and energy flow in a shallow reef flat of the northwestern PhilippinesNacorda, Hildie Maria E.; Yap, Helen T. (Springer, 1996-12)Macrofaunal biomass of the Lucero reef flat in the northwestern Philippines accounted for 9 to 52% of total sediment organic matter, and did not exhibit any significant temporal trend. The polychaetes and crustaceans consistently alternated as biomass dominants; the latter group showed monthly and seasonal variations along with the chaetognaths, molluscs, chordates, and chelicerates, among the major groups (p<0.05). Faunal abundance correlated significantly with biomass. Salinity, mean sediment grain size, sediment heterogeneity, and total organic matter were found to significantly influence faunal biomass. The sandy substrate community was characteristically heterotrophic throughout the monitoring period, i.e., P/R<1. Hourly rates of net primary production (p n ) did not exhibit any significant diurnal pattern. Monthly comparisons yielded significant differences for estimates of daily gross primary production, P, and respiration, R. Values of P were relatively low, and ranged from 2240 (± 1526 S.D.) to 4890 (± 1377) mg O2 m−2 d−1 while R ranged from 3744 (± 1504) to 6879 (± 903) mg O2 m−2 d−1. R was lower during the dry warm months than the wet months. Multiple regression analyses indicate that primary production was a positive function of light intensity and temperature, and a negative correlate of salinity (adjusted R 2 = 0.2444, p< 0.05). Respiration (r) did not appear to relate with any environmental variable, with total macroinfaunal abundance nor with biomass. Results of the study suggest that other heterotrophic components of the sand community were probably responsible for most of the energy consumption, and that these may be dependent on external sources of organic matter.
- 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.