Oil spill: Consequences for wildlife

Experts are warning that if oil reaches some parts, it could be many years before certain species and habitats recover.

The original damage to the Prestige happened almost directly over an area called the Galician Bank, 100 kilometres off the Spanish coast.

At this point, a sub-sea mountain rises from the seabed. In the upwellings of water which surround it, life thrives.

The area is acknowledged as one of the most ecologically important along the Spanish coast.

Stephan Lutter, the head of the World Wildlife Fund's North East Atlantic Programme, told BBC News Online: "It's an area very rich in fish, and as such, a source of food for seabirds."

Robin Law, a marine scientist from the Centre for Environment, Fisheries and Aquaculture Science (Cefas), told BBC News Online that while it was unlikely that fish stocks would be seriously damaged by fuel oil near the surface, seabirds would be exposed to it when they tried to feed.

So far, examples of 18 species of seabird have been found oiled by volunteers.

These include gulls and gannets, many of them migratory species common in the UK.

However, scientists are concerned about the threat to the Balearic shearwater (Puffinus mauretanicus), which is already facing extinction.

This species is now listed as critically endangered following a recent revision of its status to be published in the Spanish Red List of Threatened Bird Species.

In 1991, the population was estimated to be approximately 3,300 breeding pairs, but by 2000 this had been reportedly reduced to between 1,750 and 2,125 pairs.

At the coast

When the oil reaches coastal waters, it wreaks far more damage on fragile ecosystems, some of them vital to local human economies.

While much of the coastline of this part of Spain is rocky, there are sheltered inlets, or seas, mudflats and saltmarshes which are particularly vulnerable.

Robin Law says: "With fuel oil, when it reaches shallow waters, quite a bit will pick up sand and sink.

"Every time there is a storm, fuel oil is released out of the sand again."

Particularly under threat are filter-feeders - shellfish such as mussels - which live in this mud or sand.

They may simply be smothered by the oil as it settles, or suffocated by the oil as they try to pass tainted water through their delicate gills and feeding apparatus.

It is possible for shellfish to be tainted by the toxicity of the oil over periods of years.

This has severe implications for not only the shellfish populations themselves, but the creatures, including birds and humans, which feed on them.

A good example of this happening is a relatively small spill of fuel oil in Buzzard's Bay, US, in 1969.

This caused tainting of shellfish which was persistent many years after the incident.

While the rocky shore may be cleaned relatively quickly by storms and normal wave action, the tranquillity of the seas could delay this yet further.

Even saltmarsh plants, if severely oiled, can take up to a decade to recover fully.

According to Robin Law, efforts to clean up sensitive areas such as this can be as damaging as the oil itself.

Experts say the balance of nature on north-west Spain's rocky shores could be damaged by the spill.

Nature's repair work

Dr Paul Gilliland, a marine policy adviser with English Nature, says subtle changes could take years to correct themselves.

He said: "A common reaction is that limpets will die off.

"This may allow the growth of certain seaweeds that weaken groups of mussels.

"These could simply be washed away in the next big storm. It can take years for even rocky coasts to recover."

He said that, painful as it might be, in some cases it could be better simply not to intervene, and let nature do the repair work.

"It's human nature to want to do something, but sometimes it's better to leave it."