Community Structure and Spatial Patterns in Hard Coral Biodiversity in Selected Islands in the Gulf of Mannar, India

Abstract

The major reefs of the Gulf of Mannar Biosphere Reserve extend from the Tuticorin group of islands (Long.78 0 9’E, Lat.8 0 48’N) to the Shingle Island (Long. 79 0 14’E, Lat.9 0 14’N) in Mandapam, India. These reefs are under increasing threats from anthropogenic interventions. In view of this, a comparative study was conducted to deduce the spatial patterns in the hard coral biodiversity and community structure of five islands of the Mandapam group. The islands studied are Shingle, Krusadai, Pullivasal, Manauli and Hare. Univariate community parameters, Shannon–Wiener diversity index (H’e), Simpson diversity index, and Pielou’s evenness index were calculated for each reef in each sampling station. The highest and lowest percentage of live coral cover was recorded in the reefs of the Shingle (60.8%) and Pullivasal Islands (13.9%) respectively. Shannon index of diversity recorded maximum value in the reefs of Manauli Island (3.01) and the minimum in Pullivasal Island (1.8). Mortality indices were also derived for each island reef and the condition of the reefs was assigned as either good/sick. Relative abundance values were derived for each species and they were assigned Dominant/Abundant/ Common/Unc ommon/Rare species status. 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 end – members(CC4). Similarities between reefs were studied by Bray–Curtis similarity coefficients and maximum similarity was found between the Manauli and Hare Island reefs (56.47). The similarity matrix was subjected to ordination analysis. There was a distinct separation of reefs in the Pullivasal Island from other reefs in the MDS plot. SIMPER analysis enabled the authors to find out the species important in the community structure of each reef. From the present study it was concluded that certain coral reefs in the Gulf of Mannar ecosystem is on the threshold of degradation.