1 Introduction
Coastal lagoon is the dynamic and an ecosystem rich in biodiversity, also supports for exploitable fisheries which helped for a large scale of human population. Geographically the coastal lagoon is starched from arctic to the tropics (Nichols and Boon, 1994), covering 13% of the coastal region of the world may be ranged from<0.01 km² to>10 000 km² (Bird, 1994; Kjerfve, 1994). Regarding definition Emery and Stevenson (1957) had given the first scientific definition ever on coastal lagoon which states that “coastal lagoons are the bodies of water, separated in most cases from the ocean by offshore bars or islands of marine origin and are usually parallel to coast line”. But considering the overall salient features of lagoons, Pritchard (1967) opined that lagoons can be treated as a form of estuaries. Hence the definition of a lagoon can be same as that of an estuary i.e. “semi enclosed coastal bodies of water which has free connection with the open sea and within which the sea water is measurably diluted with the fresh water derived from land drainage”. This definition however does not include lagoons which are periodically or permanently cut off from the