New reefs found in the Great Barrier Reef ‘twilight’ zone



An international research team led by researchers from James Cook University using a high-tech underwater robot have discovered diverse coral reef communities living in the unexplored deep waters along the Great Barrier Reef shelf-edge.

Tom Bridge, a PhD Candidate in JCU’s School of Earth and Environmental Sciences, said the findings were a first for this depth of the Reef.

“These reefs occur in an area known as the mesophotic zone, or ‘twilight zone’ because of the lower light levels found there. They have been virtually unexplored because the reefs occur well below the depths accessible to most scuba divers,” Mr Bridge said.

The last few years have seen an increasing interest in deep water reefs around the world, however this was the first investigation of such habitats on the Great Barrier Reef.

Mr Bridge said the study used a recently developed robot, an Autonomous Underwater Vehicle (AUV), to investigate reef and seabed communities up to 150 metres deep along a 500 km length of the Great Barrier Reef.

Together with an international team of scientists, including University of Sydney scientist Dr Jody Webster and Dr Robin Beaman of JCU Cairns, Mr Bridge examined three sites offshore from Cairns, Townsville and Mackay.

Mr Bridge said the sites, which were located on the edge of the continental shelf, outside the outermost mapped reefs, all contained diverse coral communities comprised of a unique combination of corals.

“Some corals were members of species commonly encountered on shallow-water reefs, while others represented types rarely seen by scuba divers,” Mr Bridge said.

“Bathymetric maps of the GBR shelf-edge suggest that these deep reef habitats may be widespread in the Great Barrier Reef Marine Park, however the vast majority of them are currently unexplored.

“Understanding more about the ecology of these habitats is important due to their unique biodiversity, but also because they may provide important refuges for coral reef species from climate change impacts such as coral bleaching. There is growing evidence that some deeper reefs are buffered from these sorts of disturbances. Therefore, it is important to know more about them and to use that knowledge to better protect the biodiversity of the Great Barrier Reef”

Mr Bridge said the AUV, which records a variety of data, was operated by the Australian Centre for Field Robotics at the University of Sydney.

Mr Bridge said the vehicle took stereo-images of the sea floor in the first instance. “These images overlap so they can be stitched together into a ‘mesh’, to form a 3D image of the seafloor”.

“We then used these 3D images to obtain accurate estimates of the rugosity, or topographic complexity, and slope of the substrate, which we used to explain the distribution of the reef communities.

“The AUV also collected a variety of other environmental data including multibeam swath bathymetry, conductivity-temperature-depth, turbidity and chlorophyll.”