Marine scientists surveying a large undersea mountain chain were amazed to find millions of tiny starfish swirling their arms to capture food in the undersea current.

An expedition by 19 scientists, including five from Australia, studied the geology and biology of eight Macquarie Ridge sea mounts.

They are part of a string of underwater volcanoes — dormant for millions of years — that stretches 875 miles from south of New Zealand toward Antarctica.

Expedition leader and marine biologist Ashley Rowden said starfish usually cover only slopes away from the top of the undersea mountains.

"It got us excited as soon as we saw it," Rowden said of the site, dubbed "Brittle Star City."

"It was unique in that it [the vast brittle star grouping] hasn't been found on the tops of sea mounts before ... [and] it was over a relatively large area" of about 60 square miles, he said.

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The starfish are about 0.4 inch across, with arms about 2 inches long.

The sight of the starfishes' sweeping, mucus-coated arms in the strong current "was like herds of wildebeests sweeping majestically across the plains," Rowden said.

The expedition began March 26 and returned to port in New Zealand's capital Wellington on April 26. Commitments of key scientists in the group delayed discussion of the findings until now.

The scientists also investigated the world's biggest ocean current — the Antarctic Circumpolar Current — amid expectations they would find evidence of climate change in the Southern Ocean.

While the expedition's cameras found a wide range of corals, a high density of cardinal fish and the huge bubblegum coral, the vast collection of brittle stars was the highlight of the voyage.

"I've personally never seen anything like this — all these animals, the sheer volume — all waiting for food from the current," expedition member and marine biologist Dr. Mireille Consalvey said Monday. "It challenged what we as scientists thought we knew."

Melbourne-based marine biologist Tim O'Hara, a brittle star specialist, said the vast collection of brittle stars, or ophiuroid ophiacantha, is "like a relic of ancient times."

He said the find was like a flashback to 300 million years ago when there weren't many fish and the early relatives of brittle star used to carpet the sea floor.

"Normally fish would prey on them and eat them ... so for whatever reason there's a lack of fish predation there and it's seen this particular animal flourish," he said.

O'Hara, who was not part of the voyage, said the speed of the sea current in the area may partly explain why fish were not feeding on the tiny animals.

The Circumpolar Current merges the waters of the Atlantic, Indian and Pacific oceans and carries up to 150 times the volume of water flowing in all the world's rivers, oceanographer Mike Williams said.

Australian oceanographer Steve Rintoul, who was not involved in the expedition, said there have been few measurements of the Antarctic Circumpolar Current, which "strongly influences regional and global climate" by carrying vast amounts of water and heat across oceans.

Fewer than 200 of the world's estimated 100,000 sea mounts that rise more than a half a mile above the sea floor have been studied in any detail.