Quantitative assessment of community structure was carried out at eight stations in the Madras Harbour. Population density and trophic relationships of the biotic samples from an area of 0.1 m² were assessed and were subjected to certain useful indices of species structure and species abundance curves. Rigorous stress and pollution in one station reduces species diversity, while certain other stations show the nature of established communities in a stable environment. Detritus circuit of energy transfer is evident m the communities analysed