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The waters around the Galapagos Islands, a hotspot of biodiversity off the coast of Ecuador, have been invaded by more alien species than previously thought.

While the number of invasive species on land across the World Heritage Site听, relatively little was known about those in the marine environment.

Now field surveys have found 48 invasive species off the coasts of the islands, in addition to five known non-native species. The organisms probably hitched a ride on ships from around the world.

These surveys were undertaken only in certain habitats around two of the larger islands, so the actual number of invasive species is likely to be much greater. 鈥淔rom our knowledge of similar听studies, I wouldn鈥檛 be surprised if the number was twice [as many],鈥� says team member Jim Carlton of Williams College in听Massachusetts.

The alien species included worms, mussels, crabs and听sea squirts.听There were also tiny moss animals, such as听Amathia听verticillata, which kills seagrass and messes up fishing gear.

Seventeen of the newly-identified invaders had been spotted around the Galapagos archipelago before, but had been wrongly thought to have been native species.

The impact of these alien species on听the islands鈥� ecosystems is not yet known. But听it is likely to be negative judging from experiences elsewhere, and could threaten the islands鈥� hundreds of endemic marine species. 鈥淲hat we know is a number of these [invasive] species clearly have had impacts elsewhere in the world,鈥� says Carlton.

Invasions in other places suggest that even more harmful species could soon be headed for the waters of the Galapagos, the team warns, including soft corals that could grow rapidly over local coral, and the prospect of venomous听lionfish听crossing from the Caribbean through the听Panama Canal.

The听Galapagos Marine Reserve is protected, but it will be hard to stop further invaders because it is difficult to check for tiny species on the hull of every visiting boat.