The Galapagos Islands hosts at least 53 invasive species, ten times as many as previously thought.

The survey was conducted by a team of scientists with the Smithsonian Environmental Research Center, Williams College and the Charles Darwin Foundation, and published this week in the journal Aquatic Invasions.

Researchers began their search for non-native species in 2015 by hanging underwater settlement plates from docks on Santa Cruz and Baltra, two the archipelago's larger islands. Scientists monitored the species that attached to and grew on the plates.

The team of ecologists also sampled mangrove roots, as well as searched previous studies of Galapagos invaders.

The survey revealed 48 non-native species, mostly sea squirts, marine worms and moss animals, or bryozoans. Of the 48 species, 30 were new. Another 17 of were previously described but erroneously thought to be native.

The final species, the bryozoan Watersipora subtorquata, was first found in 1987 but wasn't identified until now. James Carlton, an emeritus professor of the Maritime Studies Program of Williams College-Mystic Seaport, scraped the species off the hull of a boat more than two decades ago.

"I carefully stored them away and faithfully kept them all these years," Carlton told UPI. "The 2015 survey offered me the chance to get the samples in front of the eyes of some expert bryozoan taxonomists."

Researchers found the bryozoan species still growing near where Carlton had found it before.

"It's still there," Carlton said. "Had I not collected it in 1987, its arrival would have been dated 2015. An accurate history of invasive species in the region is hard to come by. What we're doing is establishing a new baseline."

Watersipora subtorquata is one of several bryozoan species detailed in the new study of Galapagos invaders. Most bryozoans form colonies, and some can grow quite large.

Another one of the colonial byrozoan species identified by Carlton and his research partners is Zoobotryon verticillatum, which was recently renamed Amathia verticillata. The species is sometimes called spaghetti bryozoan or spaghetti weed. In California and Europe, the invader is known for clogging pipes, fouling fishing gear and killing seagrasses.

"We've seen colonies of spaghetti weed measuring about three feet long and a foot wide, so it's an impressive colonial animal," Carlton said. "In Southern California, I've seen colonies measuring three by six."

"Especially with climate change, these are the kinds of species that are going to benefit from a warmer Galapagos," Carlton said.

Almost all of the non-native species now found in the Galapagos arrived on the bottoms of boats. Though tourist traffic has picked up in recent decades, researchers estimate the majority of invasive species make their way to Galapagos waters on the hulls of commercial shipping vessels. And with the expansion of the Panama Canal, the risk of invasion is increasing.

Conservationists are especially worried that the Indo-Pacific lionfish, currently wreaking havoc in the Caribbean, could make its way through the Panama Canal.

To prevent the arrival of the lionfish and other damaging invaders, Galapagos authorities have created an aggressive invasive species prevention program. All international vessels entering the Galapagos Marine Reserve are inspected by divers. If non-native species are spotted on a boat's hull, the vessel must leave and be cleaned before returning.

While the prevention program is a positive, Carlton said it isn't foolproof.

"A lot of these species begin their lifecycles as tiny organisms, sizes perhaps too small for underwater divers to spot," he said.

For some time, scientists have known non-native species are making their way to the Galapagos. In 2015, researchers realized they didn't have a great sense of the scale of the invasion.

"Now, we've kind of gotten the grasp on that," Carlton said. "The next step is to nail down what the impacts on the native species."

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