Up to ten new species of starfish, sponges and brittle-star have been found during an expedition to investigate life on a range of underwater hills.

The animals were found as researchers for the Census of Marine Life discovered a unique marine habitat inhabited almost exclusively by brittle-stars.

Tens of millions of brittle-stars, a relative of the starfish, were found carpeting the flat top of a 750m (2,500ft) seamount. The habitat is part of the 870-mile (1,400km) Macquarie Ridge, a range of marine mountains running south from New Zealand. The suspected new species await confirmation by a detailed analysis of their structures and comparison with known species.

Researchers named the seamount habitat “brittle-star city” because of the vast numbers of the animal. Brittle-stars were thought to be the only animals able to keep their footing amid unusually strong currents.

The Antarctic Circumpolar Current sweeps across the flat tops of the seamounts after being funnelled by the geology of the region through a gap in the ridge. Currents rush over the ground at more than 2mph (4km/h) to create difficult and rare conditions for wildlife to survive in. Scientists have calculated that about one million cubic metres (35 million cubic feet) of seawater rush through a 50-mile stretch every second.

The brittle-stars, which have five arms around a small circular body, collect food by raising them into the current to snatch plankton and fragments of organic matter. It is thought that they have taken over the top of the seamount because the current is so strong that it sweeps away many of the predators that would otherwise control the population.

Researchers were intrigued to find other ways in which the wildlife adapted to the inhospitable conditions. Among the creatures to adapt to cope are deepwater cardinal fish, Epigonus species found sheltering below a rock ledge. By hiding from the worst of the current the fish are able to conserve energy before darting out to grab a meal.

Seamounts are among the least understood marine habitats, with fewer than 200 of the estimated 100,000 around the world that rise at least a kilometre above the sea floor having been surveyed in detail.

Mike Williams, of the National Institute of Water and Atmospheric Research in New Zealand, said that the expedition, a joint New Zealand and Australian project, should also help to determine how quickly climate change was affecting the temperatures of oceans and currents.

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