VERTICAL-DISTRIBUTION AND ABUNDANCE OF SEDIMENT DWELLING MACROINVERTEBRATES IN AN ESTUARINE MANGROVE BIOTOPE - SOUTHWEST COAST OF INDIA

Depth wise distribution of macro-invertebrates in sediments of interti dal areas of Cochin mangroves were studied The fauna mainly composed o f polychaetes, crustacerans and molluscs. At all tidal levels the macr o-fauna tended to be concentrated at the top 0-5 cm layer substratum ( 65%) and they substantially decreased towards deeper levels. The polyc haete, Marphysa gravelyi was abundant below 10 cm depth. The aggregati on and coexistence of organisms were perceptible in the apex (0-5 cm) soil. Stability of the community structure of infauna was far pronounc ed in the surface layer zone than the deeper. Anoxic condition of the deep soil and the availability of food in the atop soil determines the vertical distribution of the fauna.