In September 2026, twenty Australian university students departed Brisbane for Fiji aboard CSIRO research vessel (RV) Investigator on a CAPSTAN sea training voyage . While in coastal waters off Queensland, the students were involved in several shipwreck surveys that led to an intriguing observation.
A shipwreck surrounded by mysterious holes on the seafloor.
For some onboard, this wasn’t the first time they’d seen such a thing.
Bathymetry (seafloor mapping) of Althea II shipwreck (shown in red) surrounded by a ring of mysterious holes on the seafloor. Image: CSIRO.
The CAPSTAN team were mapping the wreck of Althea II , a popular dive wreck lying in 40 metres of water off Bundaberg in Queensland, when they made the discovery.
Lara Picton, an honours student studying geology at the Queensland University of Technology , described what they saw.
"It was really exciting to watch as we mapped the site in detail. What initially looked like a few depressions in the surface turned out to be widely spanning," Ms Picton said.
"The entire wreck is surrounded by an almost perfect circle of holes in the seabed, each typically 8 metres in diameter and 2 metres deep. We identified around 300 holes and they extend approximately 100 metres from the wreck in all directions and are the only features on an otherwise flat seafloor."
Those aboard speculated that source of the holes might be biological. A drop camera was deployed from RV Investigator to investigate further and collect vision to test this theory.
The wreck of Althea II is an oasis for marine life surrounded by a ring of mysterious holes in the seafloor. Image: CSIRO.
The site was teeming with marine life of all shapes and sizes including large fish such as rockcod. The vision collected pointed to the holes being the result of bioturbation.
Maddison Cross, a PhD candidate studying marine biology at the University of the Sunshine Coast , explained how marine life can reshape the seafloor.
“Fish, crustaceans and other marine life disturb the seafloor sediment as they feed, crawling, excavating and finding things hidden in the seafloor and may also dig burrows to lay protected within,” Ms Cross said.
“The process of livings organisms moving and mixing sediment is called ‘bioturbation’. The organisms responsible act as ecosystem engineers and can dramatically alter the shape of the seafloor,” she said.