Diversity of mangrove crabs in Kadolkele, Negombo eatuary, Sri Lanka




The present study was carried out from May 2001 to August 2001 to investigate the diversity, distribution and environmental interactions of mangrove crabs in the Kadolkele mangrove ecosystem associated with the Negombo estuary in the west coast of Sri Lanka. The data on diversity and abundance of crabs, salinity, pH, organic carbon content, moisture and temperature of the soil, ambient air temperature and floral species of mangrove were collected from three 10 m x 50 m belt transects laid perpendicular to the shore. Of the six species of crabs found in the study area, five were identified up to species level. They were Episesarma versicolor, Sesarma smithii, Sesarma guttatum, Metopograpsus thukuhar and Metopograpsus messor. This is the first record of Metopograpsus thukuhar and Sesarma guttatum in Sri Lanka. Diversity of crabs decreased with the increasing distance from the lagoon but the number of crabs present did not vary significantly (p > 0.05). The distribution of the crabs varied with the increasing distance from the lagoon. S. smithii and M. messor were distributed throughout the 50 m distance while M. thukuhar and the unidentified species were restricted to 0-20 m and 0-10 m from the lagoon respectively. E. versicolor and S. guttatum were found towards the landward side (25 - 50 m). The distribution of S. smithii showed a positive correlation (p < 0.05) with the soil salinity and soil moisture content while M. thukuhar, S. guttatum and E. versicolor showed negative correlations (p < 0.05). All species except E. versicolor showed a positive correlation with soil organic carbon content (p < 0.05). M. thukuhar showed a negative correlation with soil pH while S. guttatum and S. smithii showed a positive correlation (p < 0.05). M. thukuhar and unidentified juvenile crabs were found restricted to Rhizophora/Bruguiera zone, while E. versicolor and S. guttatum were confined to the Avicennia /Lumnitzera zone.

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