Antarctica vulnerable to invasive species carried by plastic and organic debris, oceanographic model finds

Antarctica’s unique ecosystems could be threatened by the arrival of non-native marine species and marine pollution from landmasses in the Southern Hemisphere, according to new oceanographic modeling.

In a study published today in Biology of global changeScientists from UNSW Sydney, ANU, the University of Otago and the University of South Florida suggest floating objects may be reaching Antarctic waters from more sources than previously thought.

“The increasing abundance of plastics and other human-made debris in the oceans means there are potentially more opportunities for biota to reach Antarctica,” says lead author Dr Hannah Dawson, who conducted the study as part of her PhD at UNSW and is now based at the University of Tasmania.

Non-native species, including a range of small marine invertebrates, can reach Antarctica by drifting on floating objects such as kelp, driftwood, pumice and plastic. Until now, scientists thought these species drifted only from remote, uninhabited islands in the Southern Ocean. However, this new study suggests they can reach the Antarctic coastline from all southern continents.

“We knew that kelp could be transported to Antarctica from sub-Antarctic islands, such as the Macquarie and Kerguelen Islands, but our study suggests that floating objects can reach Antarctica from much further north, including South America, New Zealand, Australia and South Africa,” says Dr Dawson.

Co-author Professor Crid Fraser from the University of Otago says kelp could deal a double blow to Antarctica’s marine ecosystem.

“Giant kelp and giant kelp are very large – often over 10 metres long – and create forest habitat for many small animals, which they can take with them on their long rafting trips to Antarctica,” she explains. “If they colonise Antarctica, marine ecosystems could change dramatically.”

Modeling the Southern Ocean

Using modeled surface current and wave data from 1997 to 2015, the team tracked the movement of floating debris from various land-based sources in the Southern Hemisphere to Antarctica, providing valuable new information on the frequency and pathways of marine dispersal.

“We were able to analyse the frequency of these rafting connections by simulating dispersal pathways over 19 years of different oceanographic conditions,” said ANU co-author Dr Adele Morrison.

“We found that floating objects reached the Antarctic coast in each of the simulated years. There seems to be a constant bombardment of anything that floats, whether it’s seaweed or a plastic bottle.”

Dr Dawson compares the computer modelling process to the game of “Poohsticks” from the children’s classic Winnie the Pooh.

“Imagine throwing a stick into a river and then running downstream to see where it ends up. That’s essentially what we’re doing with our modelling, using simulated ocean currents, instead of a river,” says Dr Dawson.

“We released millions of virtual particles, representing drifting objects, from each of the source land masses and modeled their trajectories over 19 years of estimated surface ocean currents and surface waves. After running the simulations, we could see where they would likely end up landing.

“The shortest time for particles to reach the Antarctic coast was from Macquarie Island, south of New Zealand, with some arriving in just under 9 months. On average, the longest journey was made by objects released from South America,” she explains.

Warmer waters

The research also highlights the regions of the Antarctic coastline most at risk from the arrival of non-native species.

“Most of these floating objects arrive at the tip of the Antarctic Peninsula, a region with relatively warm ocean temperatures and often no ice. These factors make it a good place for non-native species to establish themselves,” says UNSW Scientia Professor Matthew England, who is also a co-author.

The dramatic decline in Antarctic sea ice in recent years makes these rafting connections particularly worrying.

“Sea ice is very abrasive and therefore acts as a barrier to many non-native species from successfully establishing themselves around Antarctica,” says Dr Dawson.

“If the recent decline in Antarctic sea ice continues, living things floating on the surface, or attached to floating objects, could find it easier to colonize the continent, which could have major impacts on ecosystems.”