Aquatic Ecosystem - Types of Ecosystem

Global waters cover about three quarters of the earth's surface either as fresh water where salt content is less than 0.5 per cent or as saline water where the salt content is more than 3.5 per cent or as brackish water where salt content is intermediate between fresh water and saline water. On the basis of their salt content aquatic ecosystems can be divided in saline water bodies and fresh water bodies. The salt content of fresh bodies is very low, always less than 5 ppt (parts per thousand).

As against this the water bodies containing salt concentration equal to or above that of sea water (i.e., 35 ppt or above) are called as saline water bodies or marine water bodies. Seas and oceans of the world come under this category. Estuaries and brackish water bodies have salt content somewhere in between 5 to 35 ppt. Because of their salt content estuaries and oceans bear different kinds of organisms.