Species composition, abundance and diversity of mangroves in selected sites in Amprara District in the east coast of Sri Lanka

Sri Lanka is gifted with about 15,670 ha of mangrove habitats which are scattered along the coastal zone of the island. However, most of the studies on mangroves are confined to the western, north-western and southern parts of the country. Although it is been neglected, Eastern province shares 28% of the mangrove cover of the country. Thus, the main objective of the current study was to determine the distribution, abundance and diversity of true mangrove species in Pottuvil, Heda oya, Ragamwela, Panama, and Okanda mangroves in the Eastern province of Sri Lanka. Mangrove vegetation was sampled using belt transects of 5 m in width laid perpendicular to the shoreline and across the water-land gradient. True mangrove species in each transect was identified and counted. Height and DBH (Diameter at Breast Height) were recorded. Relative density, relative frequency, relative dominance and the IVI (Importance value index) of the species in each mangrove ecosystem were calculated. Shannon diversity index (H’), Shannon Evenness (E’) and Simpson index was used to compare the diversity between sites. Nine true mangrove species were recorded in Panama lagoon and the least number of species (3) were recorded from Ragamwela creek. Highest Shannon diversity value (H’ = 1.7) was obtained for the Panama mangrove which was followed by the Heda Oya Estuary mangrove (H’ = 1.1). Lowest Simpson index was recorded in Panama lagoon (0.22). Nearly half of the true mangrove species (11) that have been recorded from Sri Lanka occurs in the five study sites. They belongs to seven families and eight genera. More research is needed to understand the ecological aspects of theses mangroves as these systems have not been studied for the last thirty years. It is recommended that immediate action should be taken by the government to prevent distractive anthropogenic activities in these mangrove ecosystems.