Scientists discover never-before-seen deep reefs in Hauraki Gulf teeming with life

Scientists have discovered never-before-seen deep reefs in the Hauraki Gulf that are teeming with life.

The survey is part of a Department of Conservation (DoC) project to explore, map and protect reefs that occur in New Zealand's coastal regions beyond the reach of most scuba divers.

Researchers from Te Herenga Waka-Victoria University of Wellington and DoC spent four days in the Hauraki Gulf, using an underwater drone funded by the George Mason Charitable Trust to reach depths of 30 to 90 metres.

They explored the Alderman and Mokohinau Islands and the Colville and Craddock Channels. Their footage reveals deep reefs buzzing with life and colour, filled with thousands of fish, unique black corals, cup corals, and huge sea sponge gardens.

Professor James Bell, a Victoria University marine biologist was thrilled with what he saw. 

An underwater shot of the reef.
An underwater shot of the reef. Photo credit: Supplied

"We saw these amazing 3D sponge gardens, we also saw protected species, there were quite a few large black corals similar to Fiordland," he said.

They also saw a rare orange wandering anemone called Alicia.

"They weren't wandering, they were all sat on the black corals, something I hadn't seen before," he said.

A total of 28 deepwater sites were explored in the voyage, where organisms are part of 'mesophotic communities', meaning middle light communities. There is no longer enough light for photosynthesis so the seaweed is replaced by animals.

"Nobody has actually quantified the abundance of plants and life in these areas before. They're really important for fish species, especially ones we like to eat. We think a lot of those fish are associated in those environments because they find food there and shelter there," Prof Bell said.

Prof Bell said he was pleasantly surprised with how healthy the mesophotic reefs were, and how little damage there was from humans.

"We saw lots of fish on many of these reefs including prized recreational fish like snapper, kingfish and tarakihi, and lots of other species like pigfish, red moki, twospot demoiselle, scorpion fish, trevally. These reefs are hotspots for fish activity," he said.

The scientists found many fish.
The scientists found many fish. Photo credit: Supplied

The project is being funded by DoC, and their marine science advisor Mathilde Richer de Forges said it's about understanding where New Zealand's biodiversity is located.

"The importance of this ecosystem is really key to the health of a thriving moana, and that's something we can't oversee - we can't forget about them," she said.

That's why DoC is using this research to form a coastal and marine ecosystem classification map of deep reefs around the country, to protect those habitats from fishing and human activity like boat anchors.

"Once we can classify them we are able to identify which ones are vulnerable or which ones are rare so we can manage them," said de Forges.

It's hoped the rich biological diversity of the sites means there are also many previously undescribed marine species.