Seaweed busts isolation theory

Clumps of kelp found in Antarctica floated more than 20,000 kilometres to reach their destination, researchers have revealed.

The feat represents the longest biological rafting event ever recorded, but also serves as worrying proof that Antarctic ecosystems are not as isolated and protected from the rest of the world as previously thought.

In a paper published in the journal Nature Climate Change, a team of scientists led by Ceridwen Fraser of the Australian National University say the genomic confirmation that kelp successfully crosses several ocean currents to end up in the Antarctic means that the nature of the continent’s biology needs to be extensively rethought.

It was often thought that a combination of climate, temperature and ocean movement served to keep Antarctica effectively cut off from the rest of the world, meaning that its ecosystem was to a large extent buffered from invasive species and waterborne pollution.

The theory, however, has never been without contention. In the 1990s it became clear that deep ocean biological communities in the Antarctic and the Magellan region of South America were quite similar, although this was largely ascribed to the fact that both landmasses had once been part of the Gondwanaland supercontinent and retained ecological commonalities when they drifted apart.

By 2005 that view was challenged when scientists from the British Antarctic Survey found spider crabs from the North Atlantic off the coast of the Antarctic Peninsula. The scientists, led by Andrew Clarke, said the finding raised the question of whether the shared marine communities between the Antarctic and South America really resulted “from history … or from a previously unrecognised low level of faunal exchange”.

In the latest research, Fraser and her colleagues up the ante on the level of incursion dramatically.

Using the kelp as an example, they found that storms and ocean eddies easily push floating material across ocean currents. The apparent uniqueness of Antarctica, they say, has little to do with isolating barriers but is simply a product of the fact that most of the temperate species that get pushed towards it aren’t adapted to survive the cold.

Such species, they note, “frequently disperse to the region”. Rising ocean temperatures due to global warming, they add, will likely make it easier for some of these so-far-unsuccessful rafters to establish themselves, thus changing the composition of Antarctica’s biology.

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