Secretary-General Ban Ki-moon?Tuesday?urged governments and citizens across the global to acknowledge the enormous value of the world's oceans to humanity and ensure that pollution of the bodies of water by human activity is brought under control.

"The diversity of life in the oceans is under ever-increasing strain. Over-exploitation of marine living resources, climate change, and pollution from hazardous materials and activities all pose a grave threat to the marine environment.

"So does the growth of criminal activities, including piracy, which have serious implications for the security of navigation and the safety of seafarers," Mr. Ban said in a message to mark the World Oceans Day.

He said oceans played a key role in people's daily lives and were crucial to sustainable development, and an important frontier for research, with scientists exploring them at greater depths than ever before to discover new forms of marine life, which had the potential to advance human well-being.

"But, if we are to fully benefit from what oceans have to offer, we must address the damaging impacts of human activities," the Secretary-General said on the second annual commemoration of the Day.

He said that much action had been taken within the framework of the 1982 United Nations Convention on the Law of the Sea, the so-called "constitution for the oceans."

"But if we are to safeguard the capacity of the oceans to service society's many and varied needs, we need to do much more," he added.

The UN Scientific, Education and Cultural Organization (UNESCO) also sent out a message to highlight the importance of oceans to mankind and galvanize the world to act to stop damaging them.

"The wastes of our society, flowing from the land, and through the atmosphere, from agriculture, industry and a growing urban population can be seen in the fragile coastal waters and measured even in the centre of the water masses," the message said.

"We must collectively and unambiguously acknowledge the importance of the oceans to our existence on the planet. The ocean cleanses the air we breathe; it influences our weather, climate, and the water on which we depend."

The message was accompanied by an "Ocean Call," which appeals for priority to be given to programmes in coastal and ocean management, ocean sciences and ocean technologies.

The Intergovernmental Oceanographic Commission (IOC), a programme of UNESCO, chose the World Oceans Day to kick off events to mark its 50th anniversary.

"IOC, in partnership with other UN agencies and hundreds of associated oceanographic and marine research laboratories, is playing a vital role in addressing some of the major challenges facing the world," said UNESCO's Director-General, Irina Bokova.

The challenges include identifying and protecting marine biodiversity, monitoring global climate change and coordinating tsunami warning systems.