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Journal Articles - UP - MSI

Permanent URI for this collectionhttps://repository.unesco.gov.ph/handle/123456789/50

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1996 - 20003

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AGROVOC Keyword: search.filters.agrovoc.plant growthScientific name: search.filters.scientificname.Enhalus acoroides

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    Contrasting recolonization strategies in multi-species seagrass meadows
    Rollon, Rene N.; Van Steveninck, Erik D.De Ruyter; Van Vierssen, Wim; Fortes, Miguel D. (Elsevier BV, 1999-12)
    This study shows that in a multi-species seagrass meadow in a shallow and clear-water site, all the former seagrass species were able to recolonize in the artificially created gaps of 0.25 m2 in size within ca. 2 yr. Extrapolation of the recolonization curves of the different species predicted a full recovery within 10 yr post-disturbance. Fitted curves for the dominant species Enhalus acoroides and Thalassia hemprichii showed contrasting strategies, the latter having a comparatively high intrinsic rate, achieving full recovery within ca. 2 yr post-disturbance. E. acoroides was the latest species to establish and the projected full-recovery time was among the longest (ca. 10 yr). The effect of timing of gap creation was generally not significant (except for Syringodium isoetifolium) neither was the temporal variation in density of most species outside the gaps. As recolonization by sexual propagules was found to be low, increasing the gap size would most probably require a much longer recovery period. A crude estimate for E. acoroides would be >10 yr for 1 m2 of gap. Further, since the densities of most seagrass species vary significantly between sites, and colonization rates depend on adjacent seagrass densities, the recovery curves would also be different across sites.
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    An experimental test of the occurrence of competitive interactions among SE Asian seagrasses
    Duarte, 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.
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    Nutrient limitation of Philippine seagrasses (Cape Bolinao, NW Philippines): in situ experimental evidence
    Agawin, 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.