National Committee on Marine Sciences (NCMS)
Permanent URI for this communityhttps://repository.unesco.gov.ph/handle/123456789/6
Browse
9 results
Search Results
- Changes in community structure and biomass of seagrass communities along gradients of siltation in SE AsiaTerrados, J.; Duarte, C. M.; Fortes, M. D.; Borum, J.; Agawin, N.; Bach, S.; Thampanya, U.; Kamp-Nielsen, L.; Kenworthy, W. J.; Geertz-Hansen, O.; Vermaat, J. (Elsevier BV, 1998-05)The patterns of change in species richness and biomass of Southeast Asian seagrass communities along siltation gradients were compared at different sites in The Philippines and Thailand. Seagrass species richness and community leaf biomass declined sharply when the silt and clay content of the sediment exceeded 15%. Syringodium isoetifolium and Cymodocea rotundata were present only in multispecific meadows, while Enhalus acoroides was the only species remaining in heavily silted sediments. The following ranking of species sensitivity to siltation is proposed (from the least to most sensitive): S. isoetifolium→C. rotundata→Thalassia hemprichii→Cymodocea serrulata→Halodule uninervis→Halophila ovalis→Enhalus acoroides. Positive correlations were found between species richness and both community leaf biomass and the leaf biomass of individual seagrass species. The increase in community biomass with increasing species richness was associated with a more even distribution of the leaf biomass among seagrass species. The relationships between percent silt and clay in the sediment and seagrass community leaf biomass and species richness provide useful dose–response relationships which can be used to set allowable or threshold siltation loads in SE Asian coastal waters, and indicate that species loss from seagrass meadows is an early warning of detrimental siltation loads.
- An experimental test of the occurrence of competitive interactions among SE Asian seagrassesDuarte, C. M.; Terrados, J.; Agawin, N.; Fortes, M. D. (Inter-Research Science Center, 2000)The occurrence of competitive interactions among the seagrass species present in a multispecific SE Asian seagrass meadow was tested by the cumulative removal of shoots of an increasing number of seagrass species from the meadow in order of decreasing and increasing resource requirements for plant growth. The removal of shoots of the dominant species Thalassia hemprichii had very few effects on shoot size, shoot density and leaf area index of the extant seagrass species. The shoot density of Enhalus acoroides decreased when T. hemprichii shoots were removed, but that of Syringodium isoetifolium increased when the shoots of all the species with higher resource requirements than itself were removed from the experimental plots. The size of Halophila ovalis shoots decreased by 30% when both T. hemprichii and E. acoroides shoots were removed from the plots. The shoot density of T. hemprichii increased only when the shoots of all the accompanying species were removed from the plots. The results show that species interactions in this multispecific seagrass meadow are asymmetric. The elucidation of the nature of the interactions among seagrass species provides a key to understanding the maintenance of the high biodiversity and production that characterizes pristine SE Asian coastal ecosystems.
- Species composition and plant performance of mixed seagrass beds along a siltation gradient at Cape Bolinao, The PhilippinesBach, S. S.; Borum, J.; Fortes, M. D.; Duarte, C. M. (Inter-Research Science Center, 1998)The response of mixed Southeast Asian seagrass beds to siltation was analyzed based on field data, a transplantation experiment and experimental manipulation of light availability in seagrass populations along a silt gradient at Cape Bolinao,The Philippines. Seagrass species diversity, shoot density and depth penetration declined with increasing amounts of suspended material and increasing water column light attenuation along the silt gradient. The seagrass species could be ranked according to decreasing tolerance to siltation as: Enhalus acoroides > Cymodocea serrulata > Halodule uninervis > Thalassia hemprichii > Halophila ovalis > Cymodocearotundata > Syringodium isoetifolium. A gradual decline in shoot density and depth penetration of the different species along the silt gradient suggested that changes in the vertical light attenuation coefficient in the water column, primarily caused by differences in suspended inorganic solids, was the most important factor affecting seagrass performance. However, inconsistency among the species in response to increasing water depth, artificial shading and transplantation indicated that other factors, such as siltation-derived changes in sediment conditions, contribute to the sequential loss of seagrass species along the silt gradient.
- Proximate analysis of the flour and starch from Enhalus acoroides (L.f.) Royle seedsMontaño, M. Nemesio E.; Bonifacio, Ronald S.; Rumbaoa, Rowena Grace O. (Elsevier BV, 1999-11)The seeds of the tropical seagrass Enhalus acoroides were analyzed for their nutritive components to assess their dietary value for humans. Proximate analysis of flour prepared by grinding the dried seeds gave the following results: 9.8% moisture; 8.8% protein; 0.2% fat; 72.4% carbohydrates; 2.4% crude fiber; 6.4% ash; 933 mg/kg calcium; 2392 mg/kg phosphorous; and 2813 mg/kg iron. Correspondingly, proximate analysis of the starch prepared from the flour with a 50% yield, resulted in the following: 11% moisture; 0.8% protein; 0.1% fat; 87.6% carbohydrates; 0.4% crude fiber; 0.5% ash; 320 mg/kg calcium; 210 mg/kg phosphorous and; 220 mg/kg iron. Comparison of the proximate analysis results and the calculated caloric values of the seagrass seed flour and starch showed similarity with those of terrestrial origin.
- Observations on a multi-seagrass meadow offshore of Negros Oriental, Republic of the PhilippinesTomasko, D. A.; Dawes, C. J.; Fortes, M. D.; Largo, D. B.; Alava, M. N. R. (Walter de Gruyter GmbH, 1993)Eight species of seagrasses were encountered in a multi-species meadow offshore of Negros Oriental, Republic of the Philippines: Halodule uninervis (Forssk.) Aschers., Halodule pinifolia (Miki) Den Hartog, Cymodocea rotundata Ehrenb. et Hempr. ex Aschers., Cymodocea serrulata (R. Br.) Aschers., Syringodium isoetifolium (Aschers.) Dandy, Thalassia hemprichii (Ehrenb.) Aschers., Enhalus acoroides (L./.) Royle, and Halophila ovalis (R. Br.) Hook./. A transect survey showed that five of the eight species were quite common, with cover estimates of individual species ranging from less than 10% to over 50%. Above- and below-ground biomass and leaf productivity data were collected for at least four species at each of three stations. Above-ground biomass for combined species ranged from 125 to 250g dw m~2, and below-ground biomass of combined species ranged from 264 to 828 g dw m~2. Areal production rates for combined species ranged between 4.78 to 9.38g dw m~2 d"1, with considerable inter-specific variation. High levels of protein and low levels of soluble carbohydrate were consistent with the rapid above-ground growth observed for all species, and also suggested high growth for below-ground portions of C. serrulata, H. uninervis, S. isoetifolium, and T. hemprichii. Epiphyte loads were low compared to sister species from other locations, perhaps due to rapid blade turnover rates (up to 7.8% day"1 for S. isoetifolium).
- 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.
- The role of epiphytic periphyton and macroinvertebrate grazers in the trophic flux of a tropical seagrass communityKlumpp, D.W.; Salita-Espinosa, J. S.; Fortes, M. D. (Elsevier, 1992-11)Biomass and production of epiphytic periphyton, and the abundance, distribution and grazing rate of epifauna were measured in tropical seagrass beds in the Philippines. Periphyton comprised mainly detritus, diatoms and filamentous algae (Polysiphonia sp. 1, Centroceras clavulatum (C. Agardh) Montagne, Ceramium gracillimum Harvey and Cladophora sp.). Mean biomass of periphyton was 0.16 mg ash-free dry weight (AFDW) cm−2 frond of Enhalus acoroides (L.f.) Royle and 0.24 mg AFDW cm−2 frond of Cymodocea serrulata (R. Br.) Aschers. and Magnus. Total periphyton biomass per unit area (m2) of seagrass bed varied between habitats because of differing densities of seagrass, and ranged from 598 to 1061 mg AFDW or (24–646 mg C). Maximum (midday, summer) in situ rates of photosynthesis and respiration by epiphytes colonising artificial seagrass material averaged 11.6 μg O2 cm−2 h−1 and 2.0 μg O2 cm−2 h−1, respectively. Daily net productivity was 14 μg C cm−2 frond. Productivity of epiphytes per area of seagrass bed varied with site (36–77 mg C m−2 day−1). Relative to biomass, these data show that epiphytes are highly productive, with turnover times of 6–8 days, compared with known values of 30–100 + days for tropical seagrass fronds. The epifaunal grazer community was dominated by a few species of gastropod molluscs (especially Strombus mutabilis Swainson and Cerithium tenellum (Sowerby)). Within habitats, numbers of grazers on particular seagrass species were directly related to their available surface. Three groups of grazers were identified: those occurring on fronds day and night (e.g. S. mutabilis); those foraging over sediment during the day and fronds at night (e.g. Cerithium tenellum); those mainly confined to sediments (e.g. Strombus urceus L.). All epifaunal grazers exhibited upward movement into the seagrass canopy at night. Grazing was non-selective, removing the periphyton, except for the unutilised encrusting coralline algae, in proportion to abundance. Epifaunal grazers consumed between 20 and 62% of periphyton net production and, as in temperate systems, must therefore play a major role in the trophic flux of this tropical seagrass community.
- Growth rates and primary production of Enhalus acoroides (L.f.) royle from Lag-it, North Bais Bay, the PhilippinesEstacion, Janet S.; Fortes, Miguel D. (Elsevier, 1988-01)The growth rates and primary production of the leaves of Enhalus acoroides (L.f.) Royle at Lag-it, North Bais Bay, The Philippines, were studied from August 1982 to August 1983. Randomized complete block design showed that both rates are considerably influenced by the composite effect of spatial and temporal factors. Similarly, both are markedly bimodal. Mean growth rate was 0.93 cm day−1, with peaks in September–October and May, with lowest values in November–January. Mean production was 0.92 g C m−2 day−1, with peaks in October and March–May (Station 2) and December (Station 1) and lowest values in December (Station 2) and in June (Station 1). Growth rates significantly increased with a decrease in the percent of time the seagrass beds were exposed to air and sun in the daytime (r=−0.69), while it increased with the number of daylight hours (r=0.72). Production showed no significant correlation with either factor. Mean turnover time for the seagrass was 67 days, producing 5.5 crops annually.
- 17-year change in species composition of mixed seagrass beds around Santiago Island, Bolinao, the northwestern PhilippinesTanaka, Yoshiyuki; Go, Gay Amabelle; Watanabe, Atsushi; Miyajima, Toshihiro; Nakaoka, Masahiro; Uy, Wilfredo H.; Nadaoka, Kazuo; Watanabe, Shuichi; Fortes, Miguel D. (Elsevier, 2014)Effects of fish culture can alter the adjacent ecosystems. This study compared seagrass species compositions in 2012 with those in 1995, when fish culture was less intensive compared to 2012 in the region. Observations were conducted at the same four sites around Santiago Island, Bolinao: (1) Silaqui Island, (2) Binaballian Loob, (3) Pislatan and (4) Santa Barbara, and by using the same methods as those of Bach et al. (1998). These sites were originally selected along a siltation gradient, ranging from Site 1, the most pristine, to Site 4, a heavily silted site. By 2012, fish culture had expanded around Sites 2, 3 and 4, where chlorophyll a (Chl a) was greater in 2012 than in 1995 by one order of magnitude. Enhalus acoroides and Cymodocea serrulata, which were recorded in 1995, were no longer present at Site 4, where both siltation and nutrient load are heavy.