A Kiwi who watched the catastrophe from the shore said the specialist dive and hydrographic vessel had sunk in a marine reserve, with water depths of more than 2km, and villagers were visibly upset.

It wasn’t immediately clear how much oil was on the $100m ship, which was surveying the reef near the village of Siumu when it ran aground, prompting the evacuation of its 75 crew and passengers.

The New Zealand Defence Force said it was working with authorities “to understand the implications and minimise the environmental impacts”.

Marine ecologist Phil Ross said tropical reefs like the one it hit were typically abundant with sea life and a rich diversity of corals.

“The reef is a long way offshore, so it’s likely as pristine a reef system as you can expect to see anywhere in the tropical Pacific.”

Ross expected the wreck would cause nearby corals to die, which had knock-on effects for the sea life that relied on it.

“The diversity of sea life is closely tied to these coral habitats. There’d be fish and invertebrates living within that coral matrix and those species will be very impacted.”

Ross said the biggest question looming over ecological fallout would be whether the Manawanui could be taken off the reef.

He said nearly all of the 184m Kea Trader was removed from New Caledonia’s Durand Reef after it grounded in 2017, and its ecosystems were able to recover.

“The big question here is whether the ship is coming off, or staying on there and then breaking up and losing all its oil: I assume it was well stocked with fuel.”

Aside from the immediate risk of oil spill, Ross – who was involved with 2011′s Rena disaster off Tauranga and the 2019 grounding of the MV Solomon Trader in the Solomon Islands – said the most significant environment impacts would come from metals as they broke down over time.

“If the ship isn’t coming off that reef, then the long-term impact very much depends on what salvage activity happens.”

Unlike the challenges that salvors faced after the MV Rena wreck, he said there would at least be a detailed inventory of what cargo and potential pollutants were on the Manawanui.

Jamie Morton is a specialist in science and environmental reporting. He joined the Herald in 2011 and writes about everything from conservation and climate change to natural hazards and new technology.

Sign up to The Daily H, a free newsletter curated by our editors and delivered straight to your inbox every weekday.