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Last Updated: Friday, 11 January 2008, 12:49 GMT
Thames hit by alien mussels boom
Zebra mussel, picture courtesy of the US Geological Survey
Zebra mussels breed quickly and use up food sources
An "explosion" of alien mussels in the Thames has been caused by global warming, a scientist has said.

The population boom of zebra mussels was discovered during a study of a drained portion of the riverbed in south-west London.

The Russian species was first spotted in the Thames in 1824, but scientists believe the population growth has been caused by environmental changes.

They can damage storm drains, pipes and boats by clinging together in reefs.

Fast breeders

In November 2007, a study of 37 plots between Richmond Lock and Teddington Lock, carried out by researchers from the Marine Conservation Society, found up to 832 tiger mussels in a square metre.

A previous count of the species by a team from the University of Cambridge found 25 zebra mussels "in a five-minute walk".

We are probably seeing the start of a population explosion
Jean-Luc Solandt, Marine Conservation Society

Jean-Luc Solandt, from the Marine Conservation Society, said: "We are probably seeing the start of a population explosion.

"It depends on whether the conditions are right for them to reproduce and in the last 20 years those having been changing."

He said sea temperatures had risen and seasonal patterns of water levels in the river had been disrupted.

The striped mussels can reach up to 5cm (2ins) in length and breed quickly, blocking water intakes and robbing other species of food.

They cling to any hard surface, and their "cementing nature" can cause problems on items such as storm drains and boat propeller blades.

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