DOWNCORE DISTRIBUTION OF DIATOMS IN THE MANGROVE ECOSYSTEM OF PULICAT LAGOON, TAMIL NADU, SOUTH-EAST COAST OF INDIA

Diatoms are key components of nearly all fresh and saline environments. Most of the species are good indicators for a range of water quality, because they have narrow optima and tolerance for many environmental variables such as habitat, salinity, pH, nutrients and temperature. Diatoms respond quickly to environmental changes because they immigrate and replicate rapidly. The growth of diatoms is responsible for about 25% of the world's primary food production. In order to study the distribution of diatoms, one core of 81 cm length was retrieved from the Pulicat Lagoon, where sparse mangroves are present. The study area consist of 66 diatom species belonging to 32 genera, 21 families, 18 orders, 4 subclasses and 2 classes, of which pennates are more dominant than the centric forms. Distribution pattern of individual species were examined and their sediment relationship was determined for ecological/environmental interpretation. Sediment parameters such as CaCO3, organic matter and sand-silt-clay ratios were estimated and their downcore distribution is discussed. An attempt has been made to evaluate the favorable substrate for the abundance of diatom populations in the present study.