It comprises of the entire water mass, which may be further divided into neritic province and oceanic province.
(i) Neritic province has a depth of abotit 200 metres and has the following characteristics:
a. It receives most of the light,
b. has low salinity,
c. is less turbulent in motion, and
d. has more plant nutrients.
e. This province is, therefore, of great importance to marine life. In fact, it is able to support highest of marine life. This zone is a natural habitat of fish.
(ii) The oceanic province – This is separated from the neritic province by the edge of continental shelf. Thus, it normally has depth of more than 200 metres.
This province covers a vast geographical area and has unmatched ranges of depth. It, therefore, accounts for a large volume of water.
The province is relatively uniform in temperature and salinity.
Sunlight can penetrate only upto a depth of 200 metres. Thus, the upper zone of oceanic province receives light while below it is dark.
The water in this province is clear and has no sediments of terrestrial origin.