Threat to Diversity of Coral Reefs and its Associated Brachyuran Crabs in Gulf of Mannar Marine Biosphere Reserve

The Gulf of Mannar Marine Biosphere reserve (GoMMBR) includes 21 islands under three groups, the Mandapam, Keelakarai and the Tuticorin. A detailed survey on the diversity and density of coral reef associated brachyuran crabs was carried out in all the islands of GoMMBR. The present study shows a declining trend in the overall diversity of brachyuran crabs in Gulf of Mannar. The crab diversity is abundant in Mandapam group of islands, low in Tuticorin group and moderate in Keelakarai group. The coral mining in large quantities may be one of the reasons for limited diversity of the corals and the coral reef associated crabs in Tuticorin groups of islands. The present study reveals 21 species of crabs from 7 families. The 1997 survey report on Gulf of Mannar studied the existence of 106 species under 15 families. The wide variation from the earlier works emphasizes the decline of the coral reef associated brachyuran crabs in Gulf of Mannar. This may be due to the exploitation of corals. Sedimentation and overstress were observed more in the Tuticorin group of islands. Threats also like coral mining, sand mining, sedimentation, commercial shell collection, industrial development along the coast and pollution from the coastal towns accelerate the coral reef degradation along with its associates in the GoMMBR.