Community characteristics of mangrove species in Guimaras after an oil spill


by: Resurreccion B. Sabada*, Abner P. Barnuevo, Christy Madas, Joseph Biñas, and Edgar Hortillosa


The oil spill from M/T Solar I on August 11,2006 off southern Guimaras, Philippines released over two million liters of Bunker C industrial fuel. Visibly affected were the highly vulnerable mangroves. Spilled oil were stranded and settled in the shores affecting mangrove trees, saplings, and wildings; and including the associated resident fauna. The effect of oil spill in mangrove can be acute, secondary, and chronic and this paper focused only the acute effects of oil on the the affected mangrove flora in the affected sites in Guimaras. Specifically, the study (a) identified true mangrove species affected; (b) described the community structure; and (c) mapped the degree of oiling and areas with defoliated mangroves. The assessment was conducted on August 19 to November 18, 2006 for community structure analysis in 14 oiled sites, namely; Brgys. Dolores, Tando, Lucmayan, San Roque, La Paz (Taklong Island National Marine Reserve), Cabalagnan, Igdarapdap in Nueva Valencia; Brgys. Algeria, Sabang, Sebaste, San Isidro, Bubog in Sibunag; Igcawayan and Sebario in San Lorenzo. Two unoiled mangroves (reference sites) were also surveyed in Brgys. Getulio, Buenavista; and Lawi, Jordan. In terms of floristic composition, areas included in this assessment had 29 true mangrove species representing 14 families, or about 83% of the total number of know Philippines mangrove species. The highest floristic composition was record in Taklong Island National Marine Reserve (TINMR), in La Paz with 26 species. The most frequently occurring species were Avicennia marina, Rhizophora apiculate, R. mucronata, R. stylosa, and Sonneratia alba which occurred in 15 sites (93.8%) and they were also the dominating species with 66.66, 52.02, 27.48, 30.72, and 50.01 relative dominance respectively. Large-sized trees were found in Sebario, Igdarapdap, and Bubog with 13.31, 12.51, and 10.55 cm diameter at breast height respectively. Stand basal area ranged from 1.96 m2 ha-1 in Sebaste, to 56.36 m2 ha-1 in Bubog. The presence of large-sized S. alba in Bubog contributed greatly to its stand in basal area while relatively young or generating mangroves composed the stand of the latter. Densities per plant category vary widely per site. Wilding density was highest in Dolores with 49,567 individual ha-1 and lowest in Tando with 700 individual ha-1 ; sapling density was highest in Dolores with 2900 individual ha-1 and lowest in San Isidro with 659 individuals ha-1 ; and tree density was highest in TINMR with 3,983 individual ha-1 and lowest in Sabang with 783 individual ha-1 . Species diversity was highest in Sebaste (H’ = 1.088) and lowest in Dolores (H’ = 0.497). This high diversity is mainly attributed by the absence of the dominant species. The acute effects during the three month assessment involved the massive death of mangroves in Lucmayan, Bagatnan and Alman Sur which accounted to 0.932 ha. However, the remaining stranded oil in the mangrove area will continue to be a source of stress that cause chronic effects that are observed in a continuous and regular monitoring of the areas affected.

Keywords:Mangroves, mangrove community structure, Guimaras, oil spill