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University of Otago marine science researchers found kelp rafts washed up on southeastern New Zealand beaches had come from South Georgia in the South Atlantic and Marion Island off the coast of South Africa, while kelp found in Tasmania had come from the Kerguelen Islands in the southern Indian Ocean.
Lead author Associate Prof Ceridwen Fraser said the research emphasised the power of genomic tools for tracking species movements.
"Tens of millions of kelp rafts are drifting around the Southern Ocean, all the time connecting these coasts."
Simulated oceanographic modelling also revealed a "startling finding" that more than 10% of particles released from South Georgia reached southern New Zealand, and more than 6% reached Tasmania.
"This allowed us to build a picture of kelp rafts travelling frequently in vast numbers around the Southern Ocean and connecting land masses.
"And it’s not just the kelp itself. It’s carrying a whole lot of organisms with it," she said.
Kelp rafts could be a grouping of several plants up to 12m long, and could carry crustaceans, arthropods, isopods, crabs, molluscs, worms and starfish.
Co-author and Universidad de Concepcion researcher Dr Erasmo Macaya, of Chile, said the research showed how floating species were able to cross major oceanographic barriers, sometimes reaching the Antarctic where they were not presently part of the ecosystem.
"We also found, for the first time, the kelp was usually fully reproductive — with both male and female plants travelling — which shows they have high potential to complete the life cycle and to colonise the new territories, when the conditions will be suitable."
Many organisms were trying to shift their distributions south as the north was getting too hot, Prof Fraser said.
"Kelp and its passengers can disperse really well and reach distant land masses so are in a really good position to colonise new territory as it warms up and becomes habitable for them.
"It’s an interesting challenge which scientists are going to have to face — perhaps shifting away from the idea of conservation being about maintaining the status quo, and instead looking at managing the change to maximise biodiversity and ecosystem outcomes."