Robot submarines reveal coral catastrophe at Australia’s southernmost reef

Tiny underwater robots have captured devastating footage of coral bleaching at one of the world's most remote reefs, exposing a hidden environmental crisis off the West Australian coast.

Advanced Navigation's micro submarines, called Hydrus, surveyed Hall Bank reef near Fremantle in June, revealing a barren seafloor littered with pale, lifeless corals at the unusual latitude of 32°S.

The 7 kilogram robots created a detailed 3D digital twin of the seabed, documenting severe coral fragmentation at a site normally considered resilient due to its cold, turbid waters.

The mission comes after both the Great Barrier Reef and Ningaloo Reef suffered simultaneous bleaching events in March, triggered by marine heatwaves that pushed sea temperatures 4 degrees Celsius above summer averages.

“To truly understand the extent of coral bleaching, we need high-resolution, spatially accurate data that captures both the scale and the fine detail of change beneath the surface,” said Claudio Del Deo, co-managing director at marine consultancy O2 Marine, which collaborated on the project.

Three Hydrus units worked simultaneously, executing coordinated survey patterns across different reef sections to capture comprehensive data previously impossible with traditional diving or remotely operated vehicles.

Advanced Navigation senior AI engineer Alec McGregor said the technology revolutionises ocean data collection, which has traditionally been “slow, costly, and resource-intensive.”

“Sending divers or ROVs below 50 metres can cost tens or hundreds of thousands of dollars. Hydrus changes the equation — it can be deployed by a single person without support vessels,” McGregor said.

Hall Bank hosts a unique mix of tropical, subtropical and temperate coral species, making it a vital natural laboratory for studying climate adaptation.

Pictures: supplied

Advanced Navigation’s Hydrus unveils effects of coral bleaching at Hall Bank reef ecosystem.