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Journal Articles - UP - MSI

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AGROVOC Keyword: search.filters.agrovoc.sea grassesStart date: 1988

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    Changes in community structure and biomass of seagrass communities along gradients of siltation in SE Asia
    Terrados, 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.
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    Distribution, temporal change, and conservation status of tropical seagrass beds in Southeast Asia: 2000–2020
    Sudo, Kenji; Quiros, T. E. Angela L.; Prathep, Anchana; Luong, Cao Van; Lin, Hsing-Juh; Bujang, Japar Sidik; Ooi, Jillian Lean Sim; Fortes, Miguel D.; Zakaria, Muta Harah; Yaakub, Siti Maryam; Tan, Yi Mei; Huang, Xiaoping; Nakaoka, Masahiro (Frontiers Media SA, 2021-07-08)
    Although Southeast Asia is a hotspot of global seagrass diversity, there are considerable information gaps in the distribution of seagrass beds. Broad-scale seagrass distribution has not been updated in the global seagrass database by UNEP-WCMC since 2000, although studies on seagrasses have been undertaken intensively in each region. Here we analyze the recent distribution of tropical seagrass beds, their temporal changes, causes of decline and conservation status in Southeast Asia (plus southern mainland China, Taiwan and Ryukyu Island of Japan) using data collected after 2000. Based on the 195 literature published since 2000, we identified 1,259 point data and 1,461 polygon data showing the distribution of seagrass beds. A large discrepancy was found in the seagrass bed distribution between our updated data and the UNEP-WCMC database, mostly due to inaccurate and low resolution location information in the latter. Temporal changes in seagrass bed area analyzed for 68 sites in nine countries/regions demonstrated that more than 60% of seagrass beds declined at an average rate of 10.9% year–1, whereas 20% of beds increased at an average rate of 8.1% year–1, leading to an overall average decline of 4.7% year–1. Various types of human-induced threats were reported as causes for the decline, including coastal development, fisheries/aquaculture, and natural factors such as typhoons and tsunamis. The percentage of seagrass beds covered with existing marine protected areas (MPAs) varied greatly among countries/regions, from less than 1% in Brunei Darussalam and Singapore to 100% in southern Japan. However, the degree of conservation regulation was not sufficient even in regions with higher MPA coverage. The percentage of seagrass beds within EBSAs (Ecologically and Biologically Significant Area determined by the Convention of Biological Diversity) was higher than that within MPAs because EBSAs cover a greater area than MPAs. Therefore, designating EBSAs as legally effective MPAs can greatly improve the conservation status of seagrass beds in Southeast Asia.
    This manuscript is a contribution to the Asia-Pacific Marine Biodiversity Observation Network (AP-MBON) of the Group on Earth Observations Biodiversity Observation Network (GEO BON). We are grateful to the members of Phuket Marine Biological Center in Thailand and the Vietnam Academy of Science and Technology for providing local literature and data on seagrass bed distribution. This paper is dedicated to Chittima Aryuthaka who contributed greatly to the development of marine biology and ecology in Asia during her lifetime.
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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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    Update of seagrass cover and species diversity in Southern Viet Nam using remote sensing data and molecular analyses
    Nguyen, Xuan-Vy; Lau, Va-Khin; Nguyen-Nhat, Nhu-Thuy; Nguyen, Trung-Hieu; Phan, Kim-Hoang; Dao, Viet-Ha; Ho-Dinh, Duan; Hayashizaki, Ken-ichi; Fortes, Miguel D.; Papenbrock, Jutta (Elsevier, 2021-05)
    Along with coral reefs and mangroves, seagrass meadows are being threatened globally Southeast Asia is considered within the area of seagrasses’ cradle of diversity. However, information on the current status of seagrass beds from Southern Viet Nam is limited due to lack of reliable data about seagrass species occurring in the Southeast Asian region. One factor is the difficulty of unambiguous species identification. For example, the leaf morphological characteristics of Halophila ovalis and closely related species are overlapping which leads to misidentifications. In this study, the latest satellite Landsat 8 OLI and SENTINEL-2B image analyses were applied to determine the distribution of seagrass beds in Southern Viet Nam. Detailed morphological and genetic marker analyses were used to determine and update the species composition. The present study together with literature reviews indicate that the total area of seagrass beds from Southern Viet Nam are 10,832.1 ha. 2562 ha (or 19.1%) of seagrass coverage has been lost. The seagrass beds at Phu Quoc Island are the largest with 7579 ha. The occurrence of Halophila major is updated for almost all off-shore islands and open-water areas.
    We are deeply indebted to all staff of the Department of Marine Botany, Center for Oceanographic Data, GIS and Remote Sensing, Institute of Oceanography (ION), Viet Nam, for their support, generously providing many valuable suggestions. We thank the VAST Key lab on Food and Environmental Safety (Central Viet Nam) for the ability to use their equipment. We would like to thank the three anonymous reviewers for their suggestions, comments, and editing. We also thank to JSPS Core-toCore Program CREPSUM.JPJSCCB20200009. This work was supported by Vietnam Academy of Science and Technology, grant code VAST04.01/20-21.
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    Vegetative dynamics and sexual reproduction of monospecific Thalassia hemprichii meadows in the Kalayaan Island Group
    Rollon, Rene N.; Cayabyab, Napo M.; Fortes, Miguel D. (Elsevier BV, 2001-11)
    We surveyed eight offshore islands and shoals in the Philippine Kalayaan Island Group. The aims were to (1) map the distribution, (2) evaluate the demographic status, (3) elucidate the vegetative growth dynamics, and (4) quantify the sexual reproductive capacity of Thalassia hemprichii meadows in the region. We combined age reconstruction techniques and in situ estimations to attain such goals. We found T. hemprichii meadows only in Pag-asa Island. These meadows were generally young (mean age <1 year) and rapidly expanding (net recruitment ∼0.8 ln units per year). This was consistent with the horizontal rhizome apices being dense (162–334 apex m−2) and fast-spreading (36–56 cm per apex per year). The results for in situ measurements of plastochron interval (9.2 days), and relative leaf (3.7 cm2 cm−2 per shoot per day) and areal growth rates (2.3–2.7 cm2 per shoot per day) were similar to those of previous studies. The variation in the vertical internodal lengths showed a unimodal annual trend more distinctly in the south than in the north station, suggesting local, small-scale differences in environmental conditions between stations. Flower production was clearly seasonal, peaking around January 1999. Fruiting (128–134 m−2) and seedling recruitment (22–32 m−2) values were high, indicating a substantial contribution of sexual reproduction to the rapid expansion or meadow maintenance. The apparent disjunct occurrence of such young and highly reproductive meadows in the region merits further investigation.
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    Species composition and plant performance of mixed seagrass beds along a siltation gradient at Cape Bolinao, The Philippines
    Bach, 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.
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    Epiphyte accrual on Posidonia oceanica (L.) Delile Leaves: Implications for light absorption
    Cebrián, J.; Enríquez, S.; Fortes, M.; Agawin, N.; Vermaat, J. E.; Duarte, C. M. (Walter de Gruyter GmbH, 1999-01-01)
    We examined the pattern of epiphyte accrual along the life-span of Posidonia oceanica leaves, both for the total epiphyte community and the main epiphyte groups (i. e. red encrusting algae and brown erect algae). Moreover, we document the importance of this epiphyte accrual pattern for evaluating P. oceanica-epiphyte interactions by assessing the dependence of the quantity and quality of light absorbed by epiphytes on their accrual pattern. Epiphyte biomass increased with leaf age following a sigmoidal curve (r2 = 0.90, P < 0.001), both for the epiphyte community and for the two main groups. Total epiphyte biomass increased with leaf age at a rate of about 0.03 day−1 to reach a constant maximum value of 2.60 mg DW cm−2 on leaves older than 200 days. Brown erect algae grew about an order of magnitude faster (0.120 day−1) than red encrusting ones (0.017 day−1). However, the former group of algae reached their maximum biomass (1 mg DW cm−2) on 150 days-old leaves, whereas red encrusting algae continued to grow along the whole leaf life-span to reach a maximum biomass of 1.70 mg DW cm−2. The non-linear increase in epiphyte biomass with leaf age involved a non-linear increase in epiphyte light absorption with leaf age, which reached a maximum constant value of 30% of incident light on 250 days-old leaves. Moreover, because red encrusting algae contribute a higher fraction to total epiphyte biomass on older leaves, we observed a shift in absorbed light quality with increasing leaf-age. Our results indicate the importance of accounting for the pattern of epiphyte accrual with leaf age when assessing seagrass-epiphytes interactions, especially for long-lived seagrass species where epiphytes may differ much in growth and biomass between young and old leaves.
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    Proximate analysis of the flour and starch from Enhalus acoroides (L.f.) Royle seeds
    Montaño, 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.
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    Feeding ecology and trophic role of sea urchins in a tropical seagrass community
    Klumpp, David W.; Salita-Espinosa, J. T.; Fortes, M. D. (Elsevier BV, 1993-04)
    The grazing impact of urchins on seagrass and algal resources, and the relative importance of this to the lower-level trophic flux of a tropical seagrass community were investigated. Thalassia hemprichii (Ehrenb.) Aschers. accounted for 80–93% of seagrass frond biomass at Bolinao in the Philippines. Growth rate of seagrass was 6.6 mm per shoot day−1, or 2.3 mg AFDW per shoot day−1. Production of seagrass fronds per unit area of seagrass bed varied with location from 870 to 1850 mg AFDW m−2 day−1. Urchin density ranged from 0.9 to 4.2 m−2, with Tripneustes gratilla (L.) and Salmacis sphaeroides (L.) being the most common species. Tripneustes gratilla fed mostly on attached seagrass fronds (77–89% of diet), especially Thalassia hemprichii, whereas S. sphaeroides was a generalist, consuming Thalassia hemprichii fronds (13–65%), detached seagrass debris (5–39%), the red alga Amphiroa fragilissima (L.) Lamour. (0–30%), algal-coated sediment and rubble (0–51%) in proportions that varied with the availability of preferred food types. Live Thalassia hemprichii fronds were clearly preferred over macroalgae or dead seagrass fronds by Tripneustes gratilla, but S. sphaeroides consumed all three food types without preference. Both urchins avoided the common brown alga, Sargassum crassifolium J. Agardh. Urchins absorbed 73–76% of organic matter in seagrass fronds with epiphytes (75% of DW), and 55% of that in epiphyte-free fronds. Seagrass debris and the macroalgae A. fragilissima were of lower food quality as they were lower in organic matter, and this matter was absorbed less efficiently by urchins. Rates of ingestion (IR in g WW per urchin day−1) were proportional to body weight (W in g WW) according to the functions: IR = 0.56W0.34 (T. gratilla) and IR = 0.17W0.53 (Salmacis sphaeroides). Predicted grazing impact of urchins on seagrass resources varied spatially and temporally. Estimated annual grazing rate at the main study site was 158 g AFDW m−2, equivalent to 24% of annual seagrass production, but owing to large changes in urchin population structure and density, grazing impact is expected to vary from < 5% to > 100% at different times of year. A synthesis of knowledge on the lower-level trophic pathways in this system indicates that seagrass-urchin and periphyton-epifauna grazing interactions are both important in their contribution to overall trophic flux.
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    Observations on a multi-seagrass meadow offshore of Negros Oriental, Republic of the Philippines
    Tomasko, 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).