Diversity of true mangroves in Mandativu Island of Jaffna, Sri Lanka

Abstract

Mandativu is one of islands connected with the mainland of Jaffna and located in close proximity of Jaffna town. The extensive studies of mangroves of Jaffna Peninsula are very scanty and the literature pertaining to mangroves of Jaffna are decades old. In order to document the present day mangrove species associated with Jaffna lagoon, a study was carried out with the following objectives namely to documents the mangrove species found in Mandativu coastal line and to find out the plant cover and distribution of mangroves in the study area. The study was started from October 2013 to April, 2014. Mangrove species were identified with the help of standard keys. To document the abundance, a 30 Km2 area was selected by walking and marked points through GPS meter. Then ARCGIS software aided 5m x5m square grids were developed covering the sampling area and the random selections of grid were done via the Ms excel. The grids have marked through the GIS and the exact locations were sampled in the Mandaitivu Island. The plant species and their abundance were noted in 30 randomly selected grids. From these recordings frequency, relative frequency, density, abundance and dominance were calculated. Altogether five true mangrove species were identified namely Avicennia marina, Rhizophora mucronata, Ceriops tagal, Bruguiera cylindrica and Pemphis acidula. A. marina was the dominant species as it has the highest relative density value (0.62%). P. acidula and B. cylindrica species are rarely found in the study area. A. marina showed uniform distribution (35.8% relative frequency) while rest of the mangrove species showed clumped distribution pattern. In this study region, mangroves were cut for firewood. In conclusion, Mandaitivu Island is dominated by A. marina and B. cylindrica showed the lowest abundance. Among these A. marina is uniformly distributed and other species showed clump aggregation pattern.