Conservationists have reacted with horror to the news that cruise ships carrying up to 500 passengers have been given the green light to visit the Galapagos archipelago.

Voyages of Discovery is the first cruise company to take advantage of a controversial ruling allowing mass tourism into the islands. Until now, the fragile ecosystem has been protected by restrictions on the numbers of tourists allowed in the park at any one time. Passengers were limited to a maximum of 100 per ship — most carry far less.

The new ruling allows 12 cruise-ship visits a year, each carrying five times as many people.

David Yellow, of Voyages of Discovery, said: “Our ship will anchor in San Cristobal, where passengers will disembark to take tours in the traditional, small-scale way using local operators. Strict controls are in place; it won’t be a huge ship steaming into tiny bays and disgorging hundreds of tourists.”

Leonor Stjepic, the executive director of the Galapagos Conservation Trust, said: “We had a volcano erupt last week, but allowing cruise ships in is a far greater disaster. The islands are unique; we can’t start treating them like Ibiza.”