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Waters off Galápagos have way more alien species than previously known

  • The waters off the Galápagos Islands have nearly 10 times more alien marine invertebrates than previously recorded, a new study has found.
  • The study recorded a total of 53 non-native marine invertebrates (animals that lack a backbone, such as marine worms, sea squirts or moss animals) in the waters off two islands in the archipelago, up from five that were previously known.
  • Researchers suspect there are many more non-native species present in the Galápagos waters that remain to be discovered.

The waters off the Galápagos Islands have nearly 10 times more alien marine invertebrates than previously recorded, a recent study has found.

Located 1,000 kilometers (620 miles) off Ecuador, the Galápagos Islands are home to a unique mix of iconic plants and animals, including giant tortoises, Darwin’s finches, marine iguanas (Amblyrhynchus cristatus), and the Galápagos prickly pear (Opuntia echios). But ever since humans first arrived on the islands in the 1500s, the archipelago has seen an influx of more than 1,700 alien species, mostly introduced by humans.

While the non-indigenous species on land, such as feral cats, goats and wild blackberry, are relatively well-understood, those in the coastal waters off the islands have largely remained a mystery.

To fill this information gap, a team of researchers surveyed the seas around Santa Cruz and Baltra, two of the larger Galápagos islands. They were particularly interested in the fouling communities — organisms that settle and grow on artificial marine structures like docks, piers, hulls and harbors. With tourism, trade and transport traffic increasing in the Galápagos, these fouling communities can shed light on species that may have been introduced from other areas, researchers say.

“We know from research in other global regions, such as North America and Australia, that a large fraction of the introduced species present are associated with fouling communities, and especially artificial habitats such as docks, piers, pilings, and walls,” Gregory Ruiz, a marine biologist with the Smithsonian Environmental Research Center and co-author of the study, told Mongabay. “In essence, fouling communities and artificial substrates are ‘hotspots’ for invasions.”

However, very little research in the Galápagos has focused on such fouling communities, Ruiz added, even though the amount of artificial substrate like docks has increased in recent times.

Introduced species often settle and grow on man-made structures like this cargo dock on San Cristóbal Island in the Galápagos. Image by Inti Keith/Charles Darwin Foundation.

To see what kinds of animals grow on artificial structures around the islands, Ruiz and his colleagues hung artificial plates made of polyvinyl chloride (PVC) from three docks and allowed species to attach and grow on them for up to 14 months. They also collected samples from mangrove roots, decayed mangrove wood debris, and dock pilings, and scanned through literature and museum collections.

Overall, the team recorded a total of 53 non-native marine invertebrates (animals that lack a backbone, such as marine worms, sea squirts or moss animals) in the Galápagos. Prior to this study, only five non-native species of marine invertebrate were known.

Some 30 of the recorded species, which were newly discovered during the study, could have been living on the islands for decades, the researchers say. At the same time, 17 species that scientists have previously considered to be native will now be treated as introduced species.

“The most surprising result is the sheer number of different introduced species that we detected in our surveys, resulting in a 10-fold increase in the documented number of marine invaders in the Galápagos,” Ruiz said. “This is even more surprising when you realize the search effort was very modest, limited to only a few locations on a small portion of only two islands in the archipelago.”

Ruiz said the study was just the start of a broader analysis. “It would surprise me if there are not many more introduced species present that remain to be discovered,” he said.

John E. McCosker, the emeritus chair of aquatic biology at the California Academy of Sciences, who was not involved in the study, said he also suspected there were many more introduced species than recorded in the study.

“The authors only worked on two major islands that have human involvement, but all of the islands are now visited by tourists and commercial fishing, so there must be more introduced species, and the authors admit that,” he said.

Moreover, identifying which species are native to the Galápagos and which ones are truly introduced isn’t always straightforward. Ruiz and his colleagues, for example, were able to quickly identify some species because they are well known in other parts of the world, but for others, it took a lot of work and consultation.

“We are still uncertain about the status of many additional species detected in our surveys,” Ruiz said. “We consider these cryptogenic, meaning that we are uncertain about their geographic origins and native distributions.”

One challenge in identifying introduced species, McCosker said, is the lack of baseline information on the marine invertebrates of the Galápagos. Without this point of reference, “it is impossible for biologists to properly understand how and when these creatures were introduced,” he said. “I’m certain that as time goes on, we’ll discover that many invertebrate species that we thought were native were actually introduced.”

Ruiz said his team was working toward building baseline knowledge.

“In the case of Galápagos, many of these species could have arrived long ago and simply gone undetected until now. Certainly, ships have been arriving to Galápagos since the 1500s, and no doubt that marine species were on these vessels,” he said. “A primary goal of our work is to establish a baseline knowledge for Galápagos, to understand whether new species are still arriving, the potential impact of these species, and how best to minimize the risks of new invasions.”

The moss-like Amathia verticillata, a marine invertebrate, is known for fouling pipes and fishing gear and killing seagrasses. Image by Dan Minchin/Marine Organism Investigations.

Some of the introduced species are already a cause for concern, the researchers say. The moss-like Amathia verticillata, for example, is known for fouling pipes and fishing gear, as well as killing seagrasses. Similarly, researchers have seen the introduced date mussel (Leiosolenus aristatus) bore into coral in the Galápagos.

The impacts of many of the recorded alien marine species are, however, still unknown.

“The Galápagos Islands have one of the most stringent biosecurity programs in the world to stop new invasions,” Ruiz said. “We are working with resource managers and researchers in Ecuador to help advance invasion science that supports this important effort.”


Carlton, J. T., Keith I., and Ruiz, G. M. (2019). Assessing marine bioinvasions in the Galápagos Islands: Implications for conservation biology and marine protected areas. Aquatic Invasions 14(1), 1-20. doi:10.3391/ai.2019.14.1.01

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