Oceans carry the bulk of the world's trade, are a major source of food and employment and help regulate the planet's climate but they are under threat from pollution, over-fishing and global warming.
Governments and businesses are increasingly aware of the value of oceans but are struggling to address the many threats that imperil seas around the globe. The World Bank is steering a new global alliance on the issue.
Following are some facts about the world's oceans, the threats they face and some emerging solutions.
Oceans are Earth's most valuable asset, the World Economic Forum (WEF) says and their "natural capital" is huge, contributing $70 trillion to global gross domestic product (GDP) annually.
The value of ecosystem services oceans provide is $38 trillion annually, the WEF says.
For example, 80 percent of our oxygen comes from oceans, while the seas act as huge stores of heat and carbon, essential for regulating the climate. Seafood, reefs and tourism are major sources of jobs and wealth, while mangroves, reefs and deltas help protect coastlines.
Oceans support 90 percent of global trade volume and 40 percent of global trade value, the WEF says. More than 3.2 billion people live within 100 km (60 miles) of the sea.
Fisheries are a major source of food, providing more than 1.5 billion people with almost 20 percent of their average per-capita intake of animal protein, the U.N.'s Food and Agriculture Organisation says.
The value of fish caught in seas and inland waterways totaled $94 billion in 2008, the FAO says. The rapidly growing aquaculture sector, such as fish and shrimp farms, added a further $98.4 billion.
In 2008, an estimated 45 million people were directly engaged, full time or, more frequently, part time, in fisheries or in aquaculture. That's twice the population of Australia.
One of every six jobs in the United States is marine-related and more than a third of U.S. gross national product originates in coastal areas.
About 95 percent of the vast underwater world of all oceans is unexplored, the World Economic Forum says. Yet all of it is under threat, it says.
The United Nations Environment Program's Global Environment Outlook says three-quarters of marine fisheries are exploited up to, or beyond, their maximum capacity.
The U.N.'s most recent "State of the World's Fisheries and Aquaculture" report says 85 percent of fish stocks are fully exploited or worse.
Oceans support nearly 50 percent of all species on Earth. Many species are endangered, and some coral reefs are dying or damaged because of a combination of pollution, rising water temperatures and increasing ocean acidity as the planet heats up and the sea soaks up extra carbon dioxide from power stations, industry and cars.
Pollution from the oil and gas sector is another threat.
Masses of garbage are littered across the ocean floor or trapped in huge gyres, or rotating ocean currents, in the Pacific and elsewhere.
Large areas of protective mangroves have been also lost.
There are many and include:
Curbing the growth of carbon dioxide emissions and limiting the pace of ocean acidification. Protecting natural barriers such as coral reefs or mangroves can be a cost-effective way to reduce damage from storms.
Putting a value on the carbon stored in mangroves and sea grass beds can also lead to better protection. Boosting the network of marine protected areas, including no-take reserves, is another.
At a major U.N. meeting in Nagoya, Japan, in 2010, governments agreed to a target of protecting 10 percent of the world's oceans by 2020. Such levels of protection apply to less than 2 percent now, the World Bank says.
The United Nations says many of the benefits from nature are still taken for granted, often because there is no value assigned to them. Rethinking how businesses value nature and incorporate those values into balance sheets will refocus decision-making in board rooms towards less destructive practices, the world body says.
Sources: WEF, UNEP, NOAA, FAO, Reuters