- What is a Chinese mitten crab doing in the Thames? What's
a European zebra mussel doing in the US? What, for that matter, is an American
comb jellyfish doing in the Black Sea?
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- They've all been carried across the world in the water
used inside ships to provide stability during voyages and they now constitute
one of the world's most serious environmental problems.
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- People never realised: it was such an obscure way of
transporting potentially harmful creatures from one side of the globe to
the other that nobody gave it any thought until it was too late. But ships'
ballast water has been shown, time and again, to be the medium in which
alien invasive species have gone from a homeland where they are benign
to a new habitat where they cause environmental havoc.
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- This week in London, more than 100 countries, including
Britain, are expected to sign a UN treaty regulating the management of
ballast water by vessels around the world.
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- Its aim is to halt the spread of aquatic organisms, from
jellyfish to crabs, from algae to mussels, which can be devastating in
new ecosystems, when discharged with ballast water at a ship's destination.
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- Examples abound: the European zebra mussel is harmless
on this side of the Atlantic, but transported in ballast tanks to the Great
Lakes between Canada and the US, it causes ecological chaos, fouling underwater
structures and pipes and resulting in pollution control costing of billions
of dollars.
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- Or take the problem in geographical reverse: the comb
jellyfish fits into the ecosystem of the US but ballast-transported to
the Black Sea, it has depleted native plankton stocks so far as to cause
the near-extinction of anchovy and sprat fisheries.
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- Algae that cause toxic algal blooms are known to have
been transported and it is even suspected that epidemics of some diseases,
such cholera, may be directly caused by ballast water when a new strain
is transferred to a different part of the world.
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- Although the problem is little appreciated by the public,
it is growing urgent as world trade continues to expand and has been identified
as one of the four great threats to the health of the oceans (the others
being land-based marine pollution, over-exploitation of fish and other
natural resources, and direct destruction of marine habitat).
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- "It is an extremely serious environmental issue,"
said Efthimios Mitropoulos, secretary general of the International Maritime
Organisation (IMO), the London-based UN agency under whose aegis the treaty
is being negotiated.
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- "The fact of the matter is that ships, by carrying
thousands of tons of ballast water from one part of the world to another,
can transfer pathogens and other micro-organisms and invasive species that
have the capacity to distort and destroy the delicate balance which exists
in the ecosystem of the region where the water is offloaded."
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- Unlike oil spills and other marine pollution caused by
shipping, Mr Mitropoulos added, exotic organisms and marine species could
not be cleaned up or absorbed into the oceans. "Once introduced, they
can be virtually impossible to eliminate and, in the meantime, may cause
havoc."
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- Ballast is any material used to balance an object and
ships have carried solid ballast, in the form of rocks or sand, for thousands
of years. Modern metal vessels, however, use water, which is much easier
to pump on and off. It is essential to provide balance and stability to
ships when they are unladen.
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- A ship sailing with an empty hold will have filled its
ballast tanks at its source port, and when it reaches its destination port
and takes on cargo the ballast water will be discharged. With it may go
any number of tiny living creatures picked up at the source port through
the ballast water intakes.
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- It is not only a question of microbes and small invertebrates.
As almost all marine creatures have a phase in their life cycle when they
are only plankton-sized, almost anything can be picked up, and the possibilities
are unnerving.
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- It is estimated at least 7,000 different species are
being carried in ships' ballast tanks around the world at any one time.
The majority do not survive the journey, and even those that do usually
fail to establish a toehold at their destination because they are eaten
or out-competed by resident species. But when new species do survive and
are able to breed, they can become serious pests quite rapidly.
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- According to the IMO, the rate of bio-invasions is continuing
to increase "at an alarming rate" and new areas are being invaded
all the time. The IMO estimates that about 10 billion tons of ballast water
are transferred globally each year, but volumes of seaborne trade continue
overall to increase and the problem may not yet have reached its peak.
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- It is at least a century old. The first organism recognised
as having been spread widely by ships' ballast water is the plankton species
Odontella, which is found naturally in tropical Pacific waters but turned
up in the North Sea in 1903, causing periodic plankton blooms. But it is
only in the past 30 years that scientists have begun to see the issue as
a major threat.
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- The convention being discussed this week in London which,
if all goes well, will be signed on Friday will commit the ships of its
signatories to implement a ballast water and sediment management plan,
and may allow countries to take measures to make sure ships entering ports
are safe.
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- At present, the IMO thinks the best way for ships to
get round the threat is to discharge ballast in the open sea rather than
in port but it recognises that may not be enough, and research is going
on to see how ballast water may be treated to kill all unwanted organisms.
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- © 2004 Independent Digital (UK) Ltd
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- http://news.independent.co.uk/world/environment/story.jsp?story=489722
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