Status of Mangroves Within Taklong Island National Marine Reserve, Nueva Valencia, Guimaras, Philippines : A One-Year Post Spill Monitoring Study
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概要
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The M/T Solar I oil spill on August 11, 2006 in Guimaras, Philippines released more than 2 million liters of Bunker C affected the environmentally critical areas in Guimaras including mangroves. Acute effects involved massive mortality of mangroves that ccounted to 0.932 ha in 2006. This paper reports the monitoring period of August 2007 until September 2008 among six stations within TINMR. Specifically, the study (a) monitored the monthly and annual litter fall production; (b) assessed the defoliation rate, production of new leaves, and standing leaves of selected trees; (c) measured the leaf size of the five species monitored, and (d) assessed the mangrove community structure annually. Litter fall productions among monitored species followed a unimodal pattern with peaks during dry season extending up to June except for A. marina that extends up to August. Litterfall production varied widely depending on local environmental conditions, productivity of individual species, and habitat-specific stresses. Hence, there is difficulty in extrapolating whether the low or high volume of litterfall from this study is solely attributed to the stress caused by oilspill. However, the community structure clearly showed a drastic reduction in density and stand basal area one year after the incident. Some trees of R. apiculata, R. mucronata, and R. stylosa contiguous to the deforested area showed a significant reduction in leaf size and canopy cover that reached up to a maximum of 54.5, 57.5, and 48.1% respectively. This reduction in leaf size could mean a decrease in total photosynthetic surface area and it appears to be a manifestation of a sublethal stress on mangrove trees. Propagules of R. mucronata found in Bagatnan adjacent to the deforested area showed deformities and necrosis towards the radicle portion.In addition, necrotic and highly-grazed leaves of saplings and wildings were prevalent in R. stylosa in Bagatnan site within the deforested area. These could be another indicator of chronic stress brought about by the residual oil in the sediments wherein their weakened state made them more vulnerable to r-selected species. Salient results of this study showed the overview of the apparently struggling mangrove habitat thus, further monitoring is needed to understand deeply the recovery processes, site stability and to evaluate further if remedial strategy will be needed.
- 2010-07-26