Secrets of the Coral Sea revealed

By Karl Gruber 20 January 2016
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Researchers have discovered ancient “living fossils” and rare corals in previously uncharted depths in the Coral Sea.

A TEAM OF researchers has used a sophisticated underwater remotely operated vehicle (ROV) to reach previously unexplored depths of the Osprey Reef in the Coral Sea, off the north-eastern coast of Australia.

Osprey Reef belongs to the Coral Sea Commonwealth Marine Reserve, located east of the Great Barrier Reef, and covers almost one million A popular spot for divers, only the reef’s shallow diving spots had previously been explored in detail.

“On its seaward side, beyond the depths accessible to divers, Osprey Reef has until now been a mystery,” said lead researcher Professor Gert Wörheide of the Department of Earth and Environmental Sciences and the Geobio-Center of the Ludwig-Maximilians-Universität München in Germany.

Footage taken for the Deep Down Under expedition to Osprey Reef using the MARUM Cherokee ROV. (Copyright: MARUM University of Bremen)

Gert first explored Osprey Reef more than 20 years ago, when he found ancient organisms – so called ‘living fossils’, which have existed in the waters unchanged for millions of years – in shallow reef caves, and decided more sophisticated equipment was needed to explore deeper.

Fourteen years later, in 2009 – thanks to a grant from the German Research Foundation and working with colleagues from Germany and Australia – Gert was finally able to conduct the exploration, named the Deep Down Under expedition.

With the help of the ROV, equipped with cameras and a robotic arm, the researchers explored depths from 92m down to nearly 800m, taking photos, videos and collecting samples.

They published their findings this month in the journal Marine Biodiversity.

ROV coral sea

Cherokee ROV, supplied by MARUM – University of Bremen, in the water at Osprey Reef, Coral Sea. (Image copyright copyright MARUM – University of Bremen)

Secrets of the deep 

“Our most significant findings were the discovery of a relict fauna community consisting of rock sponges, glass sponges, brachiopods and stalked sea lilies,” said Gert. These populations were much more dominant tens to hundreds of millions of years ago, in the Paleozoic and Mesozoic eras, he said.

Their exploration also revealed different communities at different depths. In between 92m and 150m, for example, the ROV identified mostly ‘gorgonian’ corals, bush-like corals usually found in tropical waters, also known as sea whips and sea fans. Deeper down, to 450m, where almost no light gets through, the ROV found found black corals, hydro corals and soft corals.

ROV coral sea

Large spider crab (unknown species) reacting to ROV lights, from about 700m depth. (Image copyright copyright MARUM – University of Bremen)

Further down, the ROV found three different communities, depending on the type of substrate. In sandy plots, only traces of the fauna was found, such as tracks and burrows. “Those are probably from worms and crabs who live burrowed in the sediment,” explained Rob Beaman from James Cook University in Cairns, the first author of the study.

In the rocky spots covered by a thin layer of sand, the ROV found glass sponges, brachiopods, bamboo corals and spoon worms, as well as sea cucumbers and small crustaceans.

But the most interesting and densely populated habitat was that of large rocks, which were home for some unusual creatures, said Gert.

“On these rocky outcrops we found several species of glass sponges, among them two species new to science, Aspidoscopulia australia and Aspidoscopulia ospreya, which we officially named in 2011. We also found a species called Psilocalyx wilsoni, which was the first finding of this species since it was discovered during the Dutch Siboga expedition in 1899-1900 in Indonesia,” he said.

“Glass sponges formed large reefs for example in the Jurassic of Europe, but are now mainly restricted to the deep sea and colder regions, like Antarctica, where they occur in large numbers and biomass,” he added.

“These findings of rare species highlight the uniqueness of this habitat and its importance as a biodiversity hotspot.” 

ROV coral sea

The glass sponge Psilocalyx wilsoni found at about 500m depth. (Image copyright copyright MARUM – University of Bremen)