The major reefs of Gulf of Mannar Biosphere Reserve extends from Tuticorin group of islands (08048' N lat. 7809' E long.) to Shingle island (09014?N lat., 79014' E long.) in Mandapam. A comparative study was conducted on Kilakarai group of islands of this reef to deduce the spatial patterns in hard coral biodiversity and community structure. The field work was carried out during September 2004 - June 2005. The islands studied were Valai, Mulli, Appa, Valimunai and Anaipar. The highest and the lowest percentage of live coral cover was recorded by the reefs of the Mulli (40.1%) and Anaipar islands (25.0%) respectively. Shannon index of diversity recorded the maximum value in the reefs of Mulli island (2.53) and the minimum in Anaipar island (1.72). Conservation classes (CC's) of 1,2,3 or 4 were assigned to reef sites dominated by massive and submassive corals (CC1), foliose or branching non Acropora corals (CC2), Acropora corals (CC3) or approximately equal mixes of these three members (CC4). In the present study the reefs around Valai, Mulli, Appa and Valimunai islands were classified as CC2 and reef around Anaipar island was classified as CC4. Maximum similarity in species composition was found between Valai and Valimunai island reefs (58.1%). Mortality indices of all reefs classified them into the category "sick" and so further efforts should be focused on implementation of conservation strategies.

Coral reefs, community structure, biodiversity, Gulf of Mannar, spatial patterns