'Dead zones' threaten planet

krsna · March 29, 2004

Jeju - The spread of oxygen-starved "dead zones" in the oceans, a graveyard for fish and plant life, is emerging as a threat to the health of the planet, experts said here on Monday.

For hundreds of millions of people who depend on seas and oceans for their livelihoods, and for many more who rely on a diet of fish and seafood to survive, the problem is acute.

Some of the oxygen-deprived zones are relatively small, less than one square kilometre in size. Others are vast, measuring more than 70 000 square kilometres.

Pollution, particularly the overuse of nitrogen in fertilisers, is responsible for the spread of dead zones, environment ministers and experts from more than 100 countries were told.

The number of known oxygen-starved areas has doubled since 1990 to nearly 150, according to the UN Environmental Programme (Unep), holding its annual conference here.

"What is clear is that unless urgent action is taken to tackle the sources of the problem, it is likely to escalate rapidly," Unep executive director Klaus Toepfer said.

Overfishing, widening dead zones

"Hundreds of millions of people depend on the marine environment for food, for their livelihoods and for their cultural fulfilment."

The world at present gets 17% of its animal protein from fish, UN figures show.

That supply is now endangered on at least two fronts: overfishing that has depleted stocks in recent decades and now the challenge of widening dead zones.

Marion Cheatle, a senior scientist at Unep's global environment outlook division of early warning and assessment, said dead zones were in most cases the "nursery grounds" for young marine species.

"If they are affected, the replenishment of fish stock will be severely affected as well," Cheatle said.

"It is quite an urgent issue now because we know that up to now, there has been a doubling in the number of dead zones recognised over the decade."

Key emerging problem

The issue was identified as a key emerging problem in the Global Environment Year Book 2003, a health report on the planet released at the start of the Unep's three-day conference that concludes on Wednesday.

The spread of low-level oxygen zones in seas and oceans, identified as early as in the 1960s, is closely related to the overuse of fertilisers in agriculture, whose main ingredient is nitrogen.

On land, nitrogen boosts plant growth. But when it washes into the sea as rivers and rainwater overrun, it triggers an explosive bloom of algae.

When these tiny plants growing on the ocean surface sink to the bottom and decompose, they use up all the oxygen and suffocate other marine life.

With oxygen depletion, fish, oysters and other marine life eventually die out along with important habitats such as sea grass beds.

Unep said efforts should focus on cutting back on overuse of nitrogen to bring the seas back to life.