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Published 22 March 2018

Unexpected visitors - how the 2017 Dunedin Kelp Rafts came to New Zealand

Beach cast kelp rafts at Victoria Beach, Otago, with attached exotic granite rock - Jon Waters

A University of Otago study investigating the effects of major storms on marine species by studying the sub-antarctic kelp rafts has been published this week in the British interdisciplinary "Journal of the Royal Society Interface"

An unusual amount of storm activity in southern New Zealand over the past 12 months provided fresh new insight into how extreme weather events can have an impact on marine biology. 

The University of Otago team, led by the Department of Zoology’s Professor Jon Waters, used DNA and geological evidence to establish the origins of kelp rafts driven onshore by cyclonic winds in April and July, 2017.

After the storm on 21 July, numerous kelp rafts were driven onto beaches surrounding Dunedin and have come all the way from the remote sub-Antarctic Macquarie Island, well over 1000 km away from coastal Dunedin. The unusually strong southerly winds in the storm drove these rafts north, across the Subtropical Front - a major ocean barrier, allowing them to reach mainland New Zealand.

Video courtesy of the University of Otago

As the rafts travelled from so far away, several of them carried rare and unexpected passengers with them including several rocky shore species of limpets and chitons that travelled with the rafts for over 1200km across the sea.

Some of the key evidence of the rafts long journey, came from chunks of exotic rock attached to the kelp “These rocks clearly show that many of the rafts have come a long way, from very distant geological sources”, says study co-author, Professor Dave Craw from the University of Otago’s Department of Geology.

“While we have long suspected that kelp rafts can drift for long distances, these findings represent some of the longest natural rafting events ever documented anywhere”, Professor Waters says. “We’ve often wondered how some coastal species come to be distributed so widely across the Southern Hemisphere. It’s now becoming clear that storms might play a really big part in this”

For further information on this study contact