"These brittle star beds are typically found in relatively shallow areas swept by swift currents—exactly the situation in the energetic waters atop the Macquarie Ridge seamount where Brittle Star City was found," Batson said.
Two species of brittle star have been provisionally identified in the horde. One occurs around New Zealand, while the other is found almost worldwide.
Hot Spots or Not?
The find challenges prior assumptions about seamounts, which have long been considered "hot spots" of marine biodiversity containing communities of creatures unique to particular chains or even single peaks, Rowden pointed out.
"It makes us question generalizations about the uniqueness of seamounts," he said.
"Dense aggregations of brittle stars have been seen elsewhere, so you've got to start thinking, How different are seamounts in general?
"I think we are beginning to deconstruct the very simple paradigms which were erected in the 1980s and 1990s and starting to erect new ones, which are a little more subtle," he added.
However, if full analysis reveals that the brittle star population is genetically distinct, "there is a very strong argument for their protection," he said.
Bottom trawling—the use of weighted, seafloor-dragging fishing nets—for deepwater species such as orange roughy has been shown to damage seamount ecosystems. While some parts of the Macquarie Ridge are closed to trawling, Brittle Star City is not.
Rowden added that his team hopes to establish how the distribution of deepwater species changes along the Macquarie Ridge "and whether we can relate that to such features as the circumpolar current—whether it acts as a boundary between north and south dispersal for various organisms."
According to the University of Otago's Batson, the discovery demonstrates how little scientists actually know about the oceans.
"The Brittle Star City discovery is another graphic reminder that the ocean is still largely unexplored," Batson said. "Only a few hundred of the estimated 30,000 to 100,000 seamounts have been studied in any detail.
"We can only speculate on what resides on the 99 percent of seamounts that have yet to be looked at. For all we know, there are Brittle Star Cities all over the world," he added.
"Then again, the one on the Macquarie Ridge may be unique. Either way, a habitat as vigorous and spectacular as Brittle Star City is well worth treasuring and protecting."
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