Sea creatures set sail on rafts of kelp

By Julian Swallow 15 September 2010
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Barnacles, sea stars and other animals are unlikely adventurers, travelling the high seas on clumps of kelp.

AFTER A 600-KM JOURNEY from the sub-Antarctic, a variety of crustaceans, molluscs and other small marine animals have washed up on a beach in New Zealand.

Scientists say this confirms theories that these unlikely adventurers are able to travel vast distances to settle in new homes.

Associate Professor Jon Waters and Dr Ceridwen Fraser, zoologists from the University of Otago, believe that prevailing winds and water currents carried the bull kelp and its aquatic hitchhikers on the Antarctic Circumpolar Current. They drifted northwards from the Snares and Auckland island chains all the way to NZ’s South Island.

Travelling ecosystem

The team analysed six southern bull kelp specimens found on St Clair Beach in southern Otago in February 2009 and May 2010, and turned up large goose barnacles and another nine marine species, including sea spiders, snails and sea stars. The discovery solves the enduring mystery of how these animals – many sedentary – move between the continents.

Ceridwen told Australian Geographic the animals likely survived the crossing by “sheltering in the protective hollows and munching at the kelp; they eat away and eventually eat out nice protective burrows that they can shelter in.”

Vast quantities of bull kelp have been spotted floating along the current, which is driven by prevailing westerly winds at subantarctic latitudes, says Marine ecologist Professor Steve Smith with the Southern Cross University in Coffs Harbour, NSW. The new study addresses one of the ‘missing links’ in the movement of these creatures across the Southern Ocean, he says. “It provides the first real evidence for rafting as an important mode of dispersal.”

Iguana raft

Although the study focused on small crustaceans and molluscs, Ceridwen says past studies have suggested larger animals might also be able to use floating wood and seaweed to raft across oceans. The revelation sounds like it could be the sequel to the hit movie Finding Nemo.

“Iguanas were found washed up on a beach on an island in the Caribbean after a hurricane – these lizards had never before been found on the island, and it is thought they rafted over on floating wood in the storm,” she says. “Other marine creatures such as fish can also use the floating kelp as habitat and travel with it across open ocean they might otherwise avoid.”

While Ceridwen says the ability of small animals to travel and establish new colonies is “a great survival strategy, especially in the face of climate change,” her discovery may have darker implications as a method of dispersal for more invasive pests, such as Undaria seaweed.

The research is published today in the Proceedings of the Royal Society B journal.