The Deepest Coral

At 125 metres, our scientists have discovered the deepest reef coral ever found on the Great Barrier Reef. The remarkable find of a community of reef corals was made on the outer edge of the Ribbon Reefs off the north of the Barrier Reef. There are coral communities on the Great Barrier Reef existing at considerably greater depths than we could ever have imagined. A team of scientists from the Catlin Seaview Survey has discovered reef coral living at 125 metres, the deepest ever found on the Great Barrier Reef. The extreme depth is over four times the depth of the shallow reef coral habitat (0-30 m) which scuba divers can access and which has made the Great Barrier Reef such an iconic natural feature. 
 Dr. Pim Bongaerts from the Global Change Institute at the University of Queensland, who led the expedition’s deep reef team, said: “It’s intriguing. When we began our survey we were amazed to see significant coral communities at depths of around 60 metres. However, it is truly mind-blowing to see reef coral at more than twice that depth – and FOUR times deeper than most scuba divers can reach.
 We found the plating Leptoseris corals at a depth of 125 metres. Although the corals are small and the community at such depth only consists of few species, it shows that there are viable communities living down there. The corals were attached to the rock surface and were certainly not individual corals which have fallen down to this depth. 
The discovery shows that there are coral communities on the Great Barrier Reef existing at considerably greater depths than we could ever have imagined.”

More about the Survey

The Catlin Seaview Survey is sponsored by global specialty insurer Catlin Group. It is backing scientific data collection in order to better understand climate change, its risks and to inform the decisions needed to manage the consequences. The Great Barrier Reef expedition is part of an ambitious programme to survey many of the world’s coral reefs which are under threat from climate change through warming oceans and acidification of seawater as well as by coastal pollution and unsustainable fishing practices. 

Using robots to study the deep reef

Dr. Paul Muir, a taxonomist from the Museum of Tropical Queensland and team member, says: “We had extremely calm seas so were able to deploy the ROV robot on the very front of the Ribbon Reefs. Normally this part of the reef is off limits because it is fully exposed to big ocean swells and quite dangerous for any boat to anchor. However, with unusually calm seas we were able to deploy our Remotely Operated Vehicle (ROV) off the very edge of the Australian continental shelf, where the depths quickly plummet to several hundred metres." 
He continues, “Working with the ROV at these depths proved very challenging and with over 250m of cable out to provide power and communications with the ROV, it was a real struggle to collect a specimen of one of these corals. However, after quite a long battle against the dragging tether we managed to get good close-up images of several of the deep corals and collected one precious specimen from 125m.”
The Catlin Seaview Survey team has been exploring the deep to beyond 100 metres throughout its expedition, and has usually found coral populations give way to species which are no longer dependent on light, such as sponges and gorgonian fans.
In addition to finding the deepest reef corals ever found on the Great Barrier Reef the team also collected the deepest Staghorn Acropora coral. This type of coral is the largest group of reef corals taking up the majority of space on the shallow reefs and taking a range of sizes and forms. Whilst they have been recorded in deeper waters, their presence at 73 metres on the Ribbon Reefs exceeds any previous record. Summarizing the significance of the find, Dr. Bongaerts said: “Most important of all, these discoveries show just how little we really know about the Reef and how much more is yet to be discovered. This poses lots of questions for us, but now we have specimens we’ll be able to analyse them much more closely and can expect our findings to reveal a far greater understanding of just what is going on to enable reef corals to survive at such extreme depths."