The oil spill in the Galapagos is small by global pollution standards. The maximum of 240,000 gallons of diesel oil that could spill out of the tanker Jessica hardly compare to losses from Exxon Valdez, the Braer or the other famous tanker disasters in the chart, let alone the 240m gallons released during the Gulf war. On an average day, says Greenpeace, huge amounts spill from the on- going operations of oil companies and tankers. More birds and wildlife will die on UK roads today than in the Galapagos because of the spill.

But several things make the current spill unique. About a third of the islands' 600 or so native plant species are found only there. Of the 57 species of reptiles, land birds and mammals, more than 80% are found nowhere else. Among these is the world's only marine lizard, the only species of penguin and albatross found in the tropics, and a cormorant that has lived so long without predators that it has lost its ability to fly. All are uniquely vulnerable.

The spill may be small but so is the archipelago. Its surrounding seas are as much part of its ecology as the land itself. Most of the islands' animals depend on the sea for their food, directly or indirectly.

Charles Darwin, who spent five weeks there in 1839, called the Galapagos "a little world within itself" and his observations of the islands' flora and fauna helped him formulate the theory of evo lution. Since then, the 13 major and six smaller islands and 42 islets have become a symbol of ecological vulnerability and unique plant and animal species. If we cannot save the 5,000 square miles of the Galapagos, where 97% of the land and all the surrounding seas are protected and there are teams of professional scientists and conservationists working around the clock, what hope is there of saving anywhere?

Yet this spill is just the latest in a long line of threats to one of the wonders of the world. There have been dreadful droughts when thousands of animals have died of starvation, but infinitely more influential to the islands' ecology has been man. Whalers may have begun the damage by killing at least 100,000 giant tortoises for meat and oil during the 19th and 20th centuries.

Settlers brought domestic animals such as cows, pigs, donkeys, goats, cats and dogs, as well as black rats. Pigs root up tortoise nests to eat the eggs. On some islands, the rats eat every hatchling. Dogs kill tortoises up to four years old. Goats compete for food, and donkeys trample nests. Of the several hundred thousand tortoises that roamed the islands before man's arrival, fewer than 15,000 survive today and the Galapagos has seen the extinction of three of the 14 species of giant tortoises, and only a single individual remains of a fourth.

Meanwhile tourism and fishing have wreaked havoc with the marine environment. The Darwin research station on the islands has conducted autopsies on sea turtles and found they died from swallowing plastic, tossed overboard from the cruise ships. Sea lions have been found with their sensitive muzzles cut from playing with tin cans that have fallen to the ocean floor.

There are strict laws in place but they are not always followed. Tourists have made many animals dependent on them for food. Scientists have recorded marked increases in the nervousness and aggressiveness of the sea lions.

From being a natural laboratory of wildlife, the islands are becoming a laboratory to see how man affects a whole ecology. Visitors to the islands unknowingly contribute to the spread of seeds, spores and insects from one island to the next on their clothes and soles of their shoes. Newly introduced fire ants, many of which are transported on planes and boats, are expected to upset the delicate balance of the in sect population, which in turn serves as the diet of many birds.

Tourism took off in the 1960s and 70s, encouraged by the Ecuador government's need for foreign currency to service its massive external debt. Its growth led directly to an increase in immigration from the mainland; most have turned to the sea for work. The islands are now the richest region in the country and the population has increased from 6,000 to about 16,000 in the past 10 years; it is growing about 12% a year.

At the same time tourists and the immigrants are increasing the pressures on the Galapagos' already scarce resources, from fresh water to seafood. Remote fishing villages now have discos, restaurants and hotels. Local divers have reportedly devastated black coral formations, turning their catch into jewellery for tourists

Fishing has become a flash point with bands of Ecuadoreans attacking conservationists and demanding greater lobster and shark quotas from the 7m hectare marine park. In the past few months, buildings and cars belonging to conservationists have been attacked and rare captive-bred giant tortoises have been taken "hostage".