The total area of Bangladesh is about 1, 43998 square miles. The coast extends for about 480km in strait line and with the in pocket of estuaries it is about 710 km from Teknaf in the south to Khulna in the west (Mahmood, 1988). Karnaphuli is one of the most important river in Bangladesh and the Chittagong hill tract. HYPERLINK "http://en.wikipedia.org/wiki/LushaiHYPERLINK "http://en.wikipedia.org/wiki/LusThe mouth of the river hosts Chittagong’s sea port, the main port of Bangladesh. The Karnaphuli river enters into the Chittagong in the west and Southwest direction and into the Bay of Bengal in 22º 14′ N and 91º 47′ E at Patenga, leaving the city of Chittagong on its right bank, about 10 miles away from the mouth. (Rizvi, 1970) An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea (Pritchard, 1967). Estuaries form a transition zone between river environments and ocean environments and are subject to both marine influences, such as tides, waves, and the influx of saline water, and river influences, such as flows of fresh water and sediment. The inflow of both seawater and freshwater provide high levels of nutrients in both the water column and sediment, making estuaries among the most productive natural habitats in the world (McLusky, 2004). Especially in estuaries, characterized by a high degree of spatial and temporal variability, this is a prerequisite for a sound implementation of integrated management, as it will allow better predictions about future environmental changes due to human impacts (Thrush et al., 1999). The karnaphuli river estuary is one of the most important estuaries provide nursery ground and spawning ground for numerous benthos, phytoplankton, zooplankton and fish species of Bay of Bengal and those of upstream (Bhuiyan, 1977). Estuaries are amongst the most heavily populated areas throughout the world, with about 60% of the world’s population living along estuaries and the coast. As a result, estuaries are suffering degradation by many factors, including sedimentation from soil erosion from deforestation, overgrazing, and other poor farming practices, over fishing, drainage and filling of wetlands, eutrophication due to excessive nutrients from sewage and animal wastes, pollutants including heavy metals, polychlorinated biphenyls, radio nuclides and hydrocarbons from sewage inputs; and drinking or damming for flood control or water diversion (Wolanski, 2007).
Benthic macro fauna are those organisms that live on or inside the deposit at the bottom of a water body (Barnes and Hughes, 1988; Idowu and Ugwumba, 2005). Macrobenthos play as an important role in aquatic community consist of involved in mineralization, promoted and mixing of sediments and flux of oxygen into sediments, cycling of organic matter and in effort to assess the quality of inland water (Lind, 1979). According to size benthic fauna can be categorized as macrofauna (>0.5µm), meio fauna (62 µm-0.5µm) and microfauna (5,000 ind.m–2). Martins, R.T. (2008).
The fauna of the Geelong Arm and Corio Bay were first described as part of large studies: the general bay-wide study of Poore et al., (1975) and as one of the seasonally sampled stations of Poore and Rainer (1979). At least one private consultants' report also deals superfically with the benthos of the region but provides little of value for the general Port Phillip Bay study. Hossain (1983) studied on benthos of the Karnaphuly River estuary giving emphasis of pollution aspect and found higher occurrence of oligochaeta. His research indicate that some groups of benthos should be a good indicator of the pollution of an aquatic system. This research study on intertidal green mussel of the Moheskali channel was made by Kamal (1992). Islam (2003) made another investigation...