Northern invaders threaten Antarctic marine life

The Antarctic Polar Front, a strong ocean front formed where cold Antarctic water meets warmer waters to the north, has historically been seen as a barrier preventing movement of marine life.

But the study has found the Antarctic Polar Front is often crossed by floating kelp that can form rafts carrying crustaceans, worms, snails and other seaweeds across hundreds of kilometres of open ocean.

"So far, the northern species don't seem to be surviving long in the cold, icy Antarctic. But with climate change and warming oceans, many non-Antarctic species could soon colonise the region," said lead researcher Dr Ceridwen Fraser, from the ANU Fenner School of Environment and Society.

"We now know marine species from the north can easily get into Antarctic waters. The Antarctic is one of the world's fastest warming regions, and the consequences of new species establishing there could lead to drastic ecosystem changes," Dr Fraser said.

The evidence was collected by surveys of floating kelp. On three different ship voyages in 2008, 2013 and 2014, researchers counted drifting seaweed species in both sub-Antarctic and Antarctic water.

"Although we saw more seaweed north of the Polar Front, we still found lots of kelp in Antarctic water, especially just south of the Front," said co-author Professor Peter Ryan, from the University of Cape Town.

Dr Fraser said the study will help scientists to plan strategies for conserving Antarctica's unique marine life.

"We've been focusing a lot on minimising plants and animals being accidentally carried into the Antarctic by humans, for example with ship ballast water," Dr Fraser said.

"This research shows that some species can also get into the region without our help."

The research has been published in the journal Ecography.