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.
- Growth, mortality and recruitment pattern of the brown mussel, Modiolus metcalfei (Bivalvia: Mytilacea), in Panguil Bay, Southern PhilippinesTumanda, Marcelino I.; Yap, Helen T.; McManus, Liana T.; Ingles, Jose A.; López, Mai G. (Elsevier BV, 1997-08)A stock assessment study of Modiolus metcalfei in Panguil Bay, Southern Philippines, was conducted to determine growth parameters of the species and the status of the fishery given the current harvesting efforts of this resource in the bay. Growth parameter estimates yielded mean K and Lα values of 2.04 year−1 and 62.50 mm, respectively. The recruitment pattern appeared to be unimodal, with the peak occurring during the months of May–July. Spat settlement ratios for May and July were 1.6 and 2.0 spat per live adult mussel, respectively. Settling spat showed preference to attach onto the shells and exposed byssal threads of live adult mussels. Catch curve analysis showed total mortality (Z) value of 7.64 year−1; fishing mortality (F) was 5.60 year−1. Exploitation rate was 73% of total mortality, and was attributed to intensive mussel gathering by local fishermen. Fishing mortality shows an over-exploited stock that necessitates some management intervention to maintain the sustainability of the fishery resource.
- 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.
- Structure and temporal dynamics of macroinfaunal communities of a sandy reef flat in the northwestern PhilippinesNacorda, Hildie Maria E.; Yap, Helen T. (Springer, 1997)Temporal variation in macroinfaunal community structure was assessed from monthly monitoring of the sandy substrate of the Lucero reef flat in Bolinao, Pangasinan (northwestern Philippines) between November 1990 and November 1991. The community was composed of 98 taxa from 10 phyla and was consistently dominated by the polychaete family Syllidae (19–33% of monthly total abundance). Five polychaete and crustacean taxa co-dominated with the syllids and exhibited monthly shifts in dominance ranks. Overall, there was no significant change in the composition of the community after a year. Results of the study show that the temporal dynamics of the community was a function of the seasonality in salinity and of the relatively consistent nature of the substrate. Abundances of macroinfaunal crustaceans, chaetognaths, and molluscs fluctuated significantly over 12 months, and corresponded to the seasonal fluctuation in salinity. Total and polychaete abundances did not show significant monthly variation, but tended to be influenced by salinity changes. Densities of turbellarians, nemerteans, and echinoderms appeared homogeneous across 12 months, and correlated with the consistency of substrate structure in the reef flat over the experimental period. In addition, sipunculid numbers seemed to be supported by the stable amount of organic matter in the sandy substrate.
- Marine environmental problems: Experiences of developing regionsYap, Helen T. (Elsevier BV, 1992-01)The marine environmental problems of developing regions are a particular cause for concern because of the great dependence of their human populations on marine resources for survival, and because a significant portion of the world's natural heritage is threatened. Of the problems, the destruction of shallow-water ecosystems and organic (sewage) pollution are the most prominent. The environmental issues typical for Third World countries are clearly related to their socioeconomic conditions, so that attempts at solutions must possess an adequately broad perspective, i.e. they must consider all relevant aspects of a problem. There is also a great need to strengthen the capabilities of developing nations to care for their own environment.
- Using deep-belief networks to understand propensity for livelihood change in a rural coastal community to further conservationLabao, Alfonso B.; Naval, Prospero C. Jr; Yap, David Leonides T.; Yap, Helen T. (Wiley Blackwell, Inc., 2020-08)Overharvesting of terrestrial and marine resources may be alleviated by encouraging an alternative configuration of livelihoods, particularly in rural communities in developing countries. Typical occupations in such areas include fishing and farming, and rural households often switch livelihood activities to suit climate and economic conditions. We used a machine-learning tool, deep-belief networks (DBN), and data from surveys of a rural Philippine coastal community to examine household desire to change livelihood. This desire is affected by a variety of factors, such as income, family needs, and feelings of work satisfaction, that are interrelated in complex ways. In farming households, livelihood changes often occur to diversify resources, increase income, and lessen economic risk. The DBN, given its multilayer perceptron structure, has a capacity to model nonlinear relationships among factors while providing an acceptable degree of accuracy. Relative to a set of 34 features (e.g., education, boat ownership, and work satisfaction), we examined the binary response variables desire to change work or not to change work. The best network had a test set accuracy of 97.5%. Among the features, 7 significantly affected desire to shift work: ethnicity, work satisfaction, number of persons in a household in ill health, number of fighting cocks owned, fishing engagement, buy-and-sell revenue, and educational level. A cross-correlation matrix of these 7 features indicated households less inclined to change work were those engaged in fishing and retail buying and selling. For fishing, provision of economic and other incentives should be considered to encourage changing from this occupation to allow recovery of fishery resources.
- 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.