An investigation was carried out on the spatio-temporal variations of the calanoid copepod, Acartia spinicauda and the cyclopod copepod Oithona similis in relation to hydrography along Parangipettai coast,southeast coast of India during October 2002 - September 2003 covering 3 stations. The minimum and maximum values of atmospheric and surface water temperatures (°C), salinity (�), pH and dissolved

oxygen (ml l-1) were: 28.5-35.0; 28.7-34.2; 14.5-35.7; 7.4-8.6 and 3.0-7.2 respectively. The ranges (μM) of nitrate, nitrite, phosphate and silicate were 7.9-52.9; 0.6-9.6; 0.5-7.5 and 8.2-140.5 respectively. The density (No/l) of nauplii and adults of A. spinicauda and O. similis, in the surface water samples were 7- 29,000; 92-54,000 and 9-20,000; 86-46,000 espectively. The population density was more in the estuary than in the estuarine mouth and sea. When compared to O. similis, the density of A. spinicauda was found to be more throughout the year, and it may be due to the calanoid copepod�s continuous breeding, high reproductive capacity and ability to adapt to the widely changing environmental conditions.

Parangipettai, copepods, Acartia spinicauda, Oithona similis, density