Mangrove Diversity Across Salinity Gradient in Negombo Estuary-Sri Lanka

Abstract

The study was conducted in the Negombo estuarine lagoon locates in the Gampaha District of Sri Lanka. In this research, an investigation was carried out to identify and assess the distribution pattern of mangrove diversity across salinity gradient in the lagoon. A field survey was performed to collect primary data and vegetation sampling was carried out in two transects along the periphery of the lagoon. Located sample size is 5 m × 10 m. Fifteen samples were selected maintaining distribution of species heterogeneity. Only mangrove species were enumerated. In situ field-testing of salinity was carried out at monthly intervals during October 2012 to September 2013 for 15 samples. Shannon-Wiener diversity index was calculated to compare about the diversity of mangrove species. The Inverse Distance Weighted (IDW) interpolation technique in ArcGIS was performed to prepare spatial distribution maps. There are 18 mangrove species identified belonging to 14 genera and 12 families. Among them 14 species are “True” and 4 species are “Mangrove Associates”. Rhizophora mucronata, Rhizophora apiculata, Avicennia officinalis, Excoecaria agallocha and Acrostichum aureum are the most common species and Aegiceras corniculata, Aegiceras corniculata, Bruguiera sexangula and Xylocarpus granatom are the least common true mangrove species types found in the Negombo lagoon. Spatially the highest mangrove species diversity could be identified in the southern quarter and a small patch around the outlet of the lagoon. Relatively low species diversity is identified at the middle periphery of the lagoon. Spatial differences of the floristic composition and the diversity reflect the salinity tolerance ability of the different mangrove species.