News Tasmania’s deep-sea coral reef: The marvel you never knew existed
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Tasmania’s deep-sea coral reef: The marvel you never knew existed

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Solenosmilia variabilis coral reef, with seastars, sponges and urchins on the flanks of an underwater mountain south of Tasmania. Photo: CSIRO
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More spooky than pretty, and you won’t reach them with a snorkel and flippers – or even scuba gear – but newly discovered deep-sea coral beds south of Tasmania are rich with life never seen before.

The coolest thing these coral beds and reefs were found thriving on the flanks and, surprisingly, in the crevices of underwater mountains and on hillocks close to the sea floor.

This was the news brought back this week by CSIRO and Marine Biodiversity Hub scientists who spent a month aboard the research vessel Invesigator exploring a cluster of underwater mountains located in and near the Huon and Tasman Fracture marine parks.

Squat lobster, thought to be a new species. Photo: CSIRO

Because of the extent and biodiversity of these coral reefs, this seamount cluster is recognised as a globally significant ecological area.

The scientists found – living among the bioluminescent squids, ghost sharks and spook fish – more than 100 new species of marine life, including lobsters, molluscs and corals.

And for the first time, courtesy of new technologies, the scientists were able to access unexplored rocky habitats between the seamounts that were known to support deep-sea corals, in particular the main reef-building stony coral, Solenosmilia variabilis.

The deep-sea coral Calyptrophora octocoral playing nice with a brittlestar. Photo: CSIRO

The expedition surveyed 45 seamounts in total, investigated seven in detail and ventured down to the sea floor. Hi-tech camera systems travelled two metres above the floor in depths to 1900 metres, collecting 60,000 stereo images and some 300 hours of video for analysis.

Live imagery from the deep-tow camera systems revealed dense coral reefs, as well as hundreds of animals including feathery, solitary soft corals, tulip-shaped glass sponges and crinoids (also known as sea lilies) attached to the seafloor. Their colours ranged from delicate creams and pinks to striking purples, bright yellows and golds.

Coral all the way down

Chief voyage scientist Dr Alan Williams of the CSIRO said it would take months to fully analyse the coral distributions, but the researchers were cheered to find healthy deep-sea coral communities on many smaller seafloor hillocks and raised ridges away from the seamounts, to depths of 1450 metres.

A deepwater hippolytid shrimp with large hooked claw, which it uses to clean coral and get food. Photo: CSIRO

“This means that there is more of this important coral reef in the Huon and Tasman Fracture marine parks than we previously realised,” said Dr Williams in a prepared statement.

“We have identified the precise depth range in which the diverse Solenosmilia community thrives.”

He said that on the larger seamounts – those that peak in 1000 to 1250 metre depths below the sea surface – corals dominate the top 100 to 200 metres.

Damage from fishing persists 20 years later

The more detailed sampling was done on seamounts previously impacted by bottom fishing but for more than 20 years had been protected.

There was some hope that these coral communities would have begun to recover, given the length of time the area had gone unmolested. In the main, this wasn’t the case – but some life was returning to areas that had been wiped clean.

Hat maker crab, thought to be new species. Photo: CSIRO

“While we saw no evidence that the coral communities are recovering, there were signs that some individual species of corals, featherstars and urchins have re-established a foothold,” said Dr Williams.

These corals are markedly different to shallow tropical corals: they live in a cold environment without sunlight or symbiotic algae – where coral provides algae with shelter, gives coral reefs their colours and supplies both organisms with nutrients.

Deep-sea corals instead feed on tiny organisms filtered from passing currents, and protect an assortment other animals in their intricate structures.

Corals and creatures help each other out

Dr Williams said there were many instances of mutually beneficial relationships among the samples collected in a small net. Brittlestars were found curled around corals, polychaete worms had tunnelled inside corals, and corals had grown on the surface of shells.

But these deep-sea corals are fragile, slow-growing and vulnerable to human activities such as fishing, mining and climate-related changes in ocean temperatures and acidity.

Dr Williams said there was an urgent need to map the locations of deep-sea corals in the world’s oceans, and learn more about the resilience of coral-associated communities.

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