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Extreme Weather Dumps sub-Antarctic Kelp Rafts on New Zealand

An unusually large amount of storm activity in southern New Zealand over the past 12 months has provided new insights into how extreme weather events can impact marine biology.

A study published in the Journal of the Royal Society Interface (https://goo.gl/hj7QjJ) used DNA and geological evidence to establish the origins of kelp rafts driven onshore by cyclonic winds in April and July 2017. The researchers, led by Prof Jon Waters of the University of Otago, found that numerous kelp rafts driven onto Dunedin beaches by a storm on 21 July 2017 had travelled at least 1200 km from Macquarie Island. The unusually strong southerly winds drove these rafts north across the Subtropical Front, a major ocean barrier, allowing them to reach mainland New Zealand.

“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”, Waters says.

Some of the key evidence for long-distance rafting comes from exotic rocks found attached to some of the kelp rafts. “These rocks clearly show that many of the rafts have come a long way, from very distant geological sources,” says co-author Prof Dave Craw.

The study also found that rocky-shore animal species such as limpets and chitons were able to raft with the kelp to reach Dunedin. “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,” Waters says.