Year round studies on the seasonal fluctuations of environmental parameters like substrate particle, temperature, salinity, dissolved oxygen, organic carbon, phosphorus and nitrogen were made at the intertidal environment of the Vellar Estuary between August 1977 and July 1978. Composition and distribution of macro and meiofauna have also been studied at the marine, gradient and tidal zones of both the banks of the Vellar Estuary, in relation to seasons and tide levels.

Temperature variations are negligible, whereas substrate particle, salinity and oxygen are affected by flooding during the north-east monsoon. Changes in the organic carbon, nitrogen and phosphorus are related to the percentage of finer particles in the substrate. The most abundant macrofaunal groups were polychaetes, tanaids, bivalves and gastropods. Nematodes, harpacticoids, copepod nauplii and polychaetes constituted most of the meiofauna. Both macro and meiofauna were abundant during postmonsoon and summer seasons. Larger numbers of individuals belonging to different phyla were observed at the low tide level. Dominant macrofauna varied at each zone while among meiofauna, nematodes were dominant followed by harpacticoids.