Coastal areas of Antarctica were long thought to be isolated from the rest of the world through natural barriers and processes that made the icy continent impenetrable to outside organisms. Now, the discovery of invasive moss-like marine organisms pokes holes in that theory, suggesting that the southernmost ecosystem may soon be at risk from invaders.

Membranipora membranacea is a small bryozoan native to European waters that forms crusty white, lace-like colonies on inhabited algae. Like many plants, animals, and bacterium, M. membranacea travel through global waters by hitchhiking on kelp rafts driven by winds and currents. At this very moment, researchers estimate there are more than 70 million kelp rafts floating in the Southern Ocean, each like a living, floating “island” that hosts passengers from their original location as well as those picked up on route.

"Although this way of natural expansion was known in other natural ecosystems in the planet, in Antarctica, this phenomenon has taken a special scientific relevance as a potential mechanism to introduce new species in the Antarctic ecosystems", said researcher Conxita Àvila, from the Department of Evolutionary Biology, Ecology and Environmental Sciences and IRBio, in a statement.

A collaborative team of researchers from the Faculty of Biology and the Biodiversity Research Institute (IRBio), as well as the Institute of Marine Sciences (ICM-CSIC), the British Antarctic Survey (BAS), and the University of Hull collected 14 kelp rafts between 2016 and 2017 near Deception Island, a volcanic region of Antarctica. For the first time, they report finding the invasive and “ecologically harmful” M. membranacea along Antarctic shorelines.

The bryozoan has not previously been reported this far south, which means it could have a big ecological impact on the biodiversity of the region in the future. The species grows quickly and can easily colonize kelp rafts. As the moss-like organism expands, it limits the ability of local kelp to reproduce and grow and makes them more prone to breaking during storms through its hardened exterior.

"Moreover, the encrusting colonies can settle on other surfaces (plastics, boats, etc.), and plankton larvae can be transported by ballast water and survive during months. All these factors would affect the environmental balance should the species settle in Antarctica,” explained researcher Blanca Figuerola of ICM-CSIC.

The findings demonstrate that natural invasion may happen at any time and may be much easier than previously thought. Previous research has found that oceanic currents may be connecting Antarctica to the rest of the world. The drifting of algae and plastics driven by wind and marine currents can help facilitate the movement of non-native objects and living organisms to habitats already vulnerable due to climate change-related effects. Antarctica’s geographic location and proximity to South America make it particularly vulnerable to invasive species. This, coupled with high temperatures and fast ice melting across the planet, make the continent at-risk of ecosystem-altering invasions from foreign organisms.

"The Antarctic is warming, presenting new opportunities, both caused by humans and nature [sic], for animals and plants to enter Antarctic waters, changing the existing unique local communities forever,” said Huw James Griffiths of BAS.

The authors say that the effects of “passengers” in Antarctic ecosystems are largely unknown and require future monitoring in the coming years.