Millions of dead tuatua litter Northland coastline

The "tuatua apocalypse" that Whangārei woman Lisa Hoeta found while visiting Ahipara recently. Photo / Supplied

Millions of tuatua have died on Northland's west coast and again global warming could be to blame.

It comes just one week after half a million green-lipped mussels perished in hot weather combined with low tides on the same coastline.

Whangārei resident Lisa Hoeta was visiting the beach at Ahipara along Ninety Mile Beach on Northland's west coast last Thursday, when she was shocked to see the beach littered with, "millions of tuatua".

"I thought it was a tuatua apocalypse," she exclaimed.

She also said there was a huge number of dead sea snails.

"It was a sight to behold, that's for sure, I've never seen anything like it in all my life, the entire beach is just covered in them."

Hoeta said she visited the beach over two days, and on the first day the tuatua had popped through their burrows beneath the sand and they were all over the beach.

On the second day the beach was covered in sea birds and crabs, who were out to make the most of the shellfish spread.

"It was like crab city," she said.

More mass shellfish mortalities: Millions of young tuatua have presumably perished due to being "stressed out" by the heat caused by a combination of low tides and high temperatures.

"There were crabs for miles and people were running out off the beach, because they were being bitten by them, that's how many there were."

Hoeta says that the beach was covered with them for several kilometres, "it looked like the beach was made of pebbles," there were so many, she said.

Coastal science professor Chris Battershill said the mass deaths of tuatua was linked to extended periods of extreme weather linked to climate change.

"There have certainly been die-offs in the past and some times this is due to a mass settlement of pipis, they grow to huge densities then become weak through lack of food. So when a hot spell occurs, they succumb. The issue is that the frequency of these die-off events seems to be increasing."

"The marine environment is a complex one with many overlapping cycles. Through our actions with a number of additional pressures on the ocean such as pollution, enrichment, our role in global warming generally, we are taking out the resilience of 'normal' marine food webs and dynamics."

Auckland University marine scientist Dr Andrew Jeffs said the same forces that killed green-lipped mussels along the same coastline a week ago were likely behind the mass shellfish mortalities.

"Midday spring low tides with hot sunny days. The mostly baby tuatua are basically getting too hot and stressed in the sun."

However, he said it may also be linked to other effects also such as the region's drought:

"The nutrient supply that promotes the growth of microscopic plants that the tuatua filter feed may have been short of nutrients given the lack of rain in the North which washes nutrients off the land and into the sea. This could have also contributed to this."

Jeffs says as global warming tightens its grip in the region, we are likely to see more events like this.

Millions of dead tuatua on Northland's west coast could be caused by climate change. Photo / supplied.

With regards to the sea snails, Jeffs said: "It is quite possible the snails were killed by low tides and high temperatures, too."

In March 2017, millions of tuatua died and washed ashore at Waihi, however research confirmed that the event was the result of strong sea swells.

However, Jeffs was not aware of any strong swells at the time of this particular event.

He admits, "it is unusual for this to happen when there hasn't been a storm or large wave surge for a period," he said.

Ministry for Primary Industries (MPI) director of diagnostic and surveillance services Veronica Herrera is encouraging locals to report similar events as soon as they are noticed.

"This mortality event wasn't previously reported to MPI to investigate. However, since receiving this information we have dispatched fishery officers to investigate the area and collect samples.

"We strongly encourage everyone to let MPI know when mortality events like this occur because it helps us quickly get to the bottom of potential issues and enables us to rapidly source samples."

"When MPI are made aware of such events, we try to get samples as soon as possible to test for any possible presence of exotic diseases. MPI has previously investigated shellfish mass mortalities on Ninety Mile Beach and identified several possible causes including bacterial diseases. These diseases are often poorly understood, and are part of MPI's ongoing research programmes."

Hoeta said seeing so many dead shellfish was a real concern.

"Aotearoa is known for its kaimoana, if the environment is changing and causing issues with their spawning and wellbeing that could have a huge impact on whether our children and their children even get to enjoy eating them.

"Culturally it's part of our life, it's just what we do, but if they're not surviving we may have to re-evaluate that and what we as kaitiaki can do to help them, it's sad."

To report a mass shellfish death call MPI on 0800 80 9966.