Scientists have long warned that oceans worldwide are stressed. Recent reports bring more bad news: tuna fish containing mercury, a growing number of oxygen depleted zones and waters around small island nations afloat with garbage. VOA?s Zlatica Hoke reports on why everyone should be concerned.

On the northern shores of the Adriatic Sea, Croatian fishermen cherish an old adage: ?If you stick your finger into the sea, you are connected with the whole world.? Today perhaps this is true even if you don?t stick your finger into the sea.

The Adriatic Sea, a large bay off the northern Mediterranean, is part of the vast body of salt water that covers three-quarters of the earth. Even though divided into seven oceans and a multitude of seas, this body of water remains one whole. Currents and tides carry its contents from one end to another.

Increasingly, the contents are runoff chemicals, organic matter, oil and waste, produced by humans and harmful to life in the ocean. Scientists say eighty percent of pollution to the marine environment comes from land-based sources that can be as small as septic tanks, cars and trucks and as large as farms, ranches and forest areas. Coastal development aggravates the situation.

?The biggest effect of coastal development is paving over land that otherwise would allow the water that is polluted to filter before it ends up in our coastal waters,? says Christophe Tulou, president of the Center for Sea Change, a US organization promoting solutions for the protection of oceans.

?That?s one big impact. The other is filling in wetlands or converting the natural coastline in such a way that those areas which tend to be the nursery areas for our commercially important fish are destroyed,? he adds.

Christophe Tulou is also a member of the Pew Ocean Commission, an independent group of scientists, politicians and businessmen that reported on the state of US ocean waters last year. He says what people do far away from the coast, for example in the cornfields of mid-western United States, also has an impact on oceans: ?What happens is the fertilizer is put on the field, oftentimes in the fall after the harvest, and it lies there through the winter. In the spring when the snow melts and the spring rains come, a fair amount of that fertilizer, instead of going into the ground and supplying food for the plants, washes off the fields and ultimately ends up in, for example, the Mississippi River. And well over a million tons of that nitrogen flow into the Gulf of Mexico every year.?

In water, nitrogen has the same effect as in soil: it acts as a fertilizer. It promotes the growth of algae and plankton, which soak up the oxygen and suffocate other marine life, creating the so-called ?dead zones.? One of the largest is in the Gulf of Mexico. Others are scattered around the world, including such small seas as the Adriatic.

Last month the United Nations reported the number of known ?dead zones,? ranging from one square kilometer to more than 70,000 square kilometers in size, has doubled in the past decade to nearly 150.

Pollution can travel very far. A chemical once used in pesticides in Asia has accumulated in Atlantic Canada. It followed atmospheric and water flows across the Pacific, Arctic and Atlantic oceans to end up off the coast of Nova Scotia and Newfoundland in eastern Canada. Traces of arsenic, copper and zinc found on a Hawaii island were linked to smelting in China.

In the past few decades, industrialization and urbanization of Africa have increased emissions of sulphur and nitrogen oxides above the levels produced by the developed world. Some scientists warn they may add still more.

?There are a lot of areas of the world which don?t use the energy of the developed world, and they don?t have the money to put on anywhere near that much of fertilizer and have perhaps because of that used better land practice,? says Reg Watson, a marine researcher at the University of the British Columbia in Canada. ?And if their land degrades, they might do the same that has been done in many areas of the world: use more and more fertilizers.?

Reg Watson says global warming, caused by toxic gases such as carbon dioxide, is the biggest threat to oceans. Pollutants get into the water which circles around the world as if on conveyor belts, affecting global climate: ?Some of those conveyor belts of warm and cold water are what keeps the world looking the way it is now. And so one of the biggest concerns about the marine environment, and I guess the world in general, is that we might be influencing the way those conveyor belts work. But we don?t know what else that means in terms of the temperature of the sea.?

Over-fishing is another major threat to ocean life. Scientists estimate that commercial fishing during the past 50 years has caused a 90 % decline of the large predatory fish species, such as tuna, marlin, cod and haddock.

?So there are many, many species that are suffering because we are catching more fish than the ocean can replenish, says Christophe Tulou. ?Some good examples are fish like cod, which was so abundant when the first Europeans arrived on our shores that they literally could lower a basket off a ship and pull up a basket full of fish. They are now declared endangered species off the east coast of Canada.?

What?s worse, the fish that eventually finds its way to the table may not be as safe as it once was. The US Food and Drug Administration and the Environmental Protection Agency have recently warned Americans, especially pregnant women, to limit the consumption of tuna because it contains mercury, a chemical harmful to children?s development. Mercury is emitted into the air by coal-fired power plants.

If this is happening in the United States, scientists say it could be much worse in countries with fewer environment-protection laws. The United States has had clean-air and clean-water laws in place for almost half a century, and others have been added regularly to protect oceans against dumping waste from ships, overfishing and runoff pollution.

Christophe Tulou says a more concerted effort is needed: ?We have far too many laws and far too many agencies that are trying to manage ocean resources and they are not coordinating.?

And profits often get in the way. Under the pressure from some industrial states, the Environmental Protection Agency eased requirements for emission reductions that would make the air significantly cleaner.

Many scientists say to reverse the current decline of oceans, the clean-up effort must be global. Yet when it comes to signing international treaties, such as the Kyoto protocol on reduction of greenhouse emissions, many nations waver.

But some progress has been achieved, says Rebecca Lint of the National Oceanic and Atmospheric Administration. General public in many countries is getting more informed and many initiatives come from concerned citizens. She does agree efforts must be more international: ?The other thing that really works well is when these regional organizations get together they say: let?s agree on the fishing laws and if other countries don?t abide by those laws, lets put in trade restrictions and not buy their seafood products.?

Scientists say human activities everywhere impact the ocean and what happens there, affects everyone. As Cristophe Tulou says, we are all one ecosystem and we must all take care of it.