Sponges and black corals are among the spectacular species filmed by researchers surveying the underwater depths of rocky reefs in the Hauraki Gulf / Tīpaka Moana.
Using a remotely operated vehicle (ROV), the research team from Te Herenga Waka / Victoria University of Wellington was able to film at depths of 30 to 110 metres, taking footage of reef communities in and around three marine protected areas.
"We sent the ROV down 62 times, filming at reefs off the Coromandel coast near Cape Colville and Te Ruamāhua / Aldermen Islands, as well as off the north Auckland coast at Mokohīnau Islands. We found a stunning diversity of marine communities, including protected species such as black coral, and lots of marine sponges," said Professor James Bell, a marine biologist at the university.
The team has used this footage to create 3D models of the reefs, work that involved "stitching" together thousands of images collected by the ROV.
These models will provide a baseline for monitoring changes in recently created high protection areas in the gulf. Recreational and commercial fishing, discharge of waste, and disturbance of sea life through drilling or construction are banned in these areas.
It's the first time 3D models have been developed in New Zealand to monitor changes in mesophotic reefs – reefs found at depths of 30 to 150 metres, said Dr Matteo Collina, a postdoctoral research fellow at the university, who played a key role in building the models.
The research team also collected images of reefs in "control areas" that lie outside protected zones. "This information will allow us to assess how reef communities within a protected area recover and change over time compared with reefs in unprotected areas," said Professor Bell.
Video footage showed clear signs of previous human impacts in areas that are now protected.
"We found some dead black corals with fishing line wrapped around them. It's most likely the fishing line had been there long before the protected zones were created in 2025. The footage shows the potential damage that lost gear can do to fragile marine species," he said.
The survey work was funded by the Department of Conservation (DOC), which is responsible for monitoring and managing the Hauraki Gulf's marine protected areas.
"Using ROVs is an important step in applying new technologies to better understand these newly protected areas and how they recover over time," said Emma Kearney, marine technical advisor at DOC.
"Mokohīnau and Te Ruamāhua / Aldermen Islands are significant biodiversity hotspots, especially the deeper reef habitats that are beyond the reach of most divers. Working with specialists such as James and using ROVs gives us a unique opportunity to learn more about the remarkable species and ecosystems these protected areas are designed to safeguard," she said.
