The principle objective of this book is to review the biological characteristics of estuaries. The volume has been as a text for undergraduates and graduate students as well as reference for scientists conducting research on estuarine systems. And the rapid development of estuarine ecology as a field of scientific inquiry reflects a growing awareness of the immense societal importance of a coastal ecosystem. While the volume of literature on estuaries amassed, scientists deemed it necessary to synthesize the field periodically. Consiquently, several books have been produced in recent years which examine variuous aspects of the disicpline.