This Europe: Spain powerless to halt invasion of the killer mussels

The ecosystem of Spain's mighty Ebro river is under threat from a plague of mussels that are reproducing uncontrollably and clogging up the river's huge hydroelectric system.

The ecosystem of Spain's mighty Ebro river is under threat from a plague of mussels that are reproducing uncontrollably and clogging up the river's huge hydroelectric system.

The 3cm-long zebra mussel ( Dreissna polymorpha) hails originally from the Caspian and Aral seas, and was probably carried to Spain on the hull of a boat contaminated with its larva. The mussel has now taken hold in the Ebro river system, from its Mediterranean delta to the huge reservoirs upstream that straddle the regions of Aragon and Catalonia.

"The mussels carpet the river beds and reservoir floors and devour the flora and fauna, leaving the water without oxygen. Algae appear and everything dies," said Jose Luis Muzquiz, professor of infectious animal diseases at Zaragoza University.

The killer mussel was first detected in Spanish waters last year but attempts to stop its frenetic proliferation failed. Last September there were colonies of 2,000 mussels per cubic metre, now there are 40,000 per cubic metre.

As well as the risk of causing an ecological catastrophe, the mussel clogs up water pipes, filters and hydroelectric plants.

Spain's electrical giant Endesa has set up a working group to try to counter the plague. "We are investigating how and where we can stop the mussels' advance," said Antonio Palau, who leads the project.

Expensive and elaborate countermeasures include artificial waves, heat treatment or poisons. They could only be used in closed lakes and are of no use in the Ebro.

"We can kill them off in the hydroelectric machinery with strong chemicals," said Dr Muzquiz. "But we can't put toxins in rivers and reservoirs that supply so much of the nation's water supply."