Some ecological aspects of the mangroves on the west coast of Sri Lanka

Abstract

Mangrove formation (mangals) on the west coast are not extensive and, in most places, are limited to narrow strips bordering river mouths and estuaries. A clear ecological zonation is difficult to discern, except for a Rhizophora-Bruguiera zone at the edge of the water followed by a zone containing the other core species. The low level of tidal amplitude as well as persistend and long-term human interference are major factors that led to the limitation of mangroves to narrow strips and to the disappearence or non-establishment of proper ecological zonation. Floristic composition of wet zone mangroves is somewhat different from that of dry zone mangroves. This difference appears to be due to prevailling salinity differences, wet zone mangroves experiencing lower salinity conditions and dry zone mangroves experiencing higher salinity conditions. In each zone, there are riverine and estuarine mangroves. Four types of high salinity (dry zone) estuarine mangroves, viz, fringing, scrub, overwash, and basin, could be distinguished depeding on the geomorphic and flooding characteristics. Basin mangroves are not found on the west coast. MAngroves in Sri Lanka have been subjected to man's detrimental interference to a greater or lesser degree for a long time. In the north-east, mangroves have received relatively less interference, but, those on the west and south-west coasts have been highly interfered with, and in some cases, mangroves have virtually disappeared. Urgent conservation measures are requaired to save Sri Lankan mangroves