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National Committee on Marine Sciences (NCMS)

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Author: search.filters.author.Borum, J.

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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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    Relationship between sediment conditions and mangrove Rhizophora apiculata seedling growth and nutrient status
    Duarte, C. M.; Geertz-Hansen, O.; Thampanya, U.; Terrados, J.; Fortes, M. D.; Kamp-Nielsen, L.; Borum, J.; Boromthanarath, S. (Inter-Research Science Center, 1998)
    The growth rate and nutritional status of Rhizophora apiculata seedlings were analyzed across mangrove stands with different sediment composition in The Philippines and Southern Thailand. Plant growth differed 10-fold and the production of new leaves, roots and branches varied between 50- and 100-fold across sites. Most (>60%) of the variance in mangrove growth rate across systems could be accounted for by differences in the nutrient concentration of the leaves, which was in turn related to the interstitial nutrient concentration and the silt plus clay content of the sediments. Nutrient-poor coarse sediments were characteristic of mangroves located in the mouths of rivers draining small watersheds, while sediments at the mouths of large rivers had high silt, clay, and nutrient contents, thus allowing the development of nutrient-sufficient, fast-growing R. apiculata seedlings. The growth of R. apiculata seedlings increased significantly when the plants grew adjacent to rivers draining areas >10 km2. The results provide evidence that growth of R. apiculata seedlings at the edge of the progressing mangrove forests is often nutrient limited, and that the extent of nutrient limitation depends on the delivery of silt and nutrients from the rivers. The coastal zones adjacent to small (<10 km2) drainage areas seem unsuitable to support adequate growth of R. apiculata seedlings, and afforestation programmes should, therefore, target mud flats adjacent to large rivers instead.
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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.