Vast new marine metropolis found near NZ

NIWA

DEEP DOWN: Dense aggregation of brittlestars on rock with arms feeding in water current.

NIWA

PRETTY COLOURS: Close up of corals and sponges on seabed.

WATER WONDERS: Close up of invertebrates on seabed. Includes corals, seastar and sponges.

NIWA

NEW UNDERWATER COLONY: Map showing the location of Macquarie Ridge.

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A vast new underwater colony labelled "Brittlestar City" has been found south of New Zealand by government scientists.

Details of the major find have been announced by the National Institute of Water and Atmospheric Research at a biodiversity conference in Oslo over the weekend.

Millions of starfish-like creatures have been found on a peak 90 metres below the sea surface on the subsea Macquarie Range stretching 1,400km south of New Zealand.

They dubbed the peak, filmed with a robot submarine in April, Brittlestar City after the five-armed creatures related to starfish, sea cucumbers, sea lilies, and sea urchins.
Tens of millions live arm tip to arm tip in a swirling circumpolar current flowing over and around it at roughly four kilometers per hour.

It allows Brittlestar City's life to capture passing food simply by raising their arms, and it sweeps away fish and other hovering would-be predators.

Discovery of this marine metropolis highlighted a month-long April expedition to survey the Macquarie Ridge aboard the NIWA’s research ship Tangaroa.

Scientists photographed brown-black brittlestars numbering hundreds per square meter and estimate tens of millions of them populate the 100 square km flat top of the seamount.

"We were excited to see such a huge assemblage of brittlestars on the Macquarie Ridge seamount," NIWA ecologist Ashley Rowden said in a press release from Science Daily at the conference.

"Not only is it amazing to see a vast array of one type of organism but the implications of the find for our understanding of the relative uniqueness of seamount assemblages are potentially far-reaching.".

The eight biologists on board believe some species collected have never before been recorded in the region while some may be new to science.

An abundance of deepwater cardinal fishes was found sheltering below a rock ledge on the seamount. In the lee of the rock, biologists believe, the fish could both conserve energy and access food.

Cod were found in the folds of a large bubblegum coral (nearly two meters high, and likely hundreds of years old). These fish were also believed to be finding shelter from the current and perhaps benefiting in other ways from their close association with the coral.

Rowden said aggregations like this had never before been observed.

"It's this sort of information will allow us to improve our knowledge of biodiversity in the deep sea, and how best to manage it," Rowden said.

- © Fairfax NZ News