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At last, the game may be up for marine invaders that hitch free rides across the globe in ships’ ballast water. A global convention to stop this happening was formally triggered on 8 September, more than two decades after it was proposed, and will officially come into force a year from then.

The convention will compel many of the world’s 70,000 or so registered cargo ships to install equipment guaranteed to kill off any aquatic creatures in seawater taken on board to maintain stability.

Ships often discharge their ballast at distant destinations, and for decades this has led to hugely damaging introductions of new and invasive species from one part of the world into another.


“The ones with the biggest economic and ecological impact have probably been the North American comb jelly, Mnemiopsis leidyi, and the European zebra mussel, Dreissena polymorpha,” says Natasha Brown, a spokeswoman for the International Maritime Organization, the UN body that will administer the Ballast Water Management Convention.

The arrival of the comb jelly (pictured top) in the Black, Azov and Caspian seas from its home on the east coast of North America caused the catastrophic collapse of fisheries in the 1990s.

Crossing in the opposite direction as larvae, zebra mussels (pictured below) have caused an estimated $1 billion worth of damage between 1989 and 2000 in the US Great Lakes by blocking water intake pipes.

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David Smith of Plymouth Marine Laboratory in the UK says that a ship can carry more than 100,000 tonnes of ballast water, and that the world’s shipping fleet relocates as much as 7 billion tonnes of water each year. The ballast water can contain thousands of different species ranging from larger zooplankton organisms down to the eggs and larvae of others, plus abundant colonies of bacteria.

With the convention coming into force, this invasion route – one of the greatest threats to the world’s oceans – should be dramatically curtailed. But it will take time. “There aren’t enough facilities around the world to immediately fit all the world’s ships with the necessary sterilisation equipment,” says Smith.

Although the convention was proposed in 1991 and adopted by the IMO in 2004, it could not come into force until countries that collectively represent 35 per cent of the world’s shipping tonnage had ratified it. That threshold was reached on 8 September when Finland signed up, bringing the total number of signatories to 52.

Most ships registered in or visiting signatory countries will eventually be compelled to fit on-board systems to eliminate stowaways in ballast water.

More than 60 systems for doing this, including ones that use filters, ultraviolet light, or chlorination, have been approved in accordance with IMO guidelines.

Pay-off

Smith points out that some countries where a significant proportion of the world’s ships are registered, such as Panama – accounting for a fifth of the world’s carrying capacity – have not yet signed up.

But Brown says that the ships of non-signatory nations will be subject to the convention when sailing in the waters of signatories. “We hope it may encourage other countries to move forward with ratification,” she says.

The US hasn’t signed the convention because the US Coast Guard has its own benchmarks for the efficiency of ballast clean-up. Although it mirrors the IMO requirements, there are some differences.

Because the US has set different standards to the IMO for assessing the effectiveness of treatment systems, this may discourage ship-owners from fitting equipment until they know which systems satisfy both regimes, says Smith.

But the Coast Guard has welcomed the triggering of the convention as an important global step towards combating the movement of invasive species.

“Although the US is not a signatory to the convention, we have domestic legislation that implements nearly identical ballast water discharge standards for vessels operating in US waters,” said a US Coast Guard spokeswoman. “We look forward to continued work with IMO to align US and international requirements as closely as possible.”

Since this story was published, the way that the Ballast Water Management Convention can affect ships of non-signatory countries has been made clearer.