Ocean

The word "sea" is often used interchangeably with "ocean", but strictly speaking a sea is a body of saline water (possibly a division of the World Ocean) partly or fully enclosed by land.
An ocean (from Ancient Greek Ὠκεανὸς (Okeanos); the World Ocean of classical antiquity) is a body of saline water that composes a large part of a planet's hydrosphere. In the context of Earth, it refers to one or all of the major divisions of the planet's World Ocean – they are, in descending order of area, the Pacific, Atlantic, Indian, Southern (Antarctic), and ArcticOceans.
The origin of Earth's oceans is still unknown though they are believed to have first appeared in the Hadean period and may have been the point of origin for the emergence of life. The total volume is approximately 1.3 billion cubic kilometres (310 million cu mi) with an average depth of 3,682 metres (12,080 ft). It is the habitat of 230,000 known species, however much of the ocean's depths remain unexplored and it is estimated that over two million marine species may exist.
Coral reef degradation is unfortunately not a new phenomenon. 
A 2011 report from the World Resources Institute found that three-quarters of the world’s coral reefs are threatened by increased stress from pollution and climate change. Corals are very sensitive to temperature, 
But because they are stationary, they cannot migrate to find their prime habitat. 
So as ocean temperatures warm, the coral organisms die, leaving just the white skeletal structures, a phenomenon known as bleaching.As Oceana marine scientist Matthew Huelsenbeck said at the event:
“There is only one word that I can use that sums up this proposal: unacceptable.
 The levels of impacts to protected dolphins and whales, including critically endangered species like the North Atlantic right whale are simply unacceptable.”Yesterday Oceana and its supporters braved foul weather to protest a truly foul idea. Armed with airhorns and megaphones they gave the Department of the Interior (DOI) a tiny preview of what is in store for the ocean’s inhabitants should the Department allow seismic airgun testing to go forward in the Atlantic Ocean.....
 You tube: ocean