Massive mussels in NZ waters replicated in new research

A team of scientists are trying to replicate an almost extinct type of mussel that once played an important role in the ecology of the Hauraki Gulf.

Horse mussels used to line the sea floor in many parts of Aotearoa, but over the past two decades they have been decimated by destructive fishing methods.

The research is moving from lab to ocean, in the hope of giving fish and shellfish more places to live and help to restore struggling fisheries.

Horse mussels are not your average mussels that you can find along rocky shores, beaches and in supermarkets.

They are massive, growing up to nearly half a metre long.

Horse mussels once covered estuaries and harbours across Aotearoa, but they have been mostly wiped out by some types of commercial fishing, such as scallop dredging.

Over the years, sediment has also washed off land and smothered the mussel beds.

University of Auckland marine scientist Jenny Hillman said without the mussels, the sea floor had not been the same.

"We have degraded our coastal systems, to a huge level because of taking too much and the way we take as well.

"So, a lot of it has been dredging, in this case a lot of it has been dredging for scallops, but the scallop and the horse mussel habitat overlap.

"Because of the way that you dredge, you take everything, even if it's not what you want."

Horse mussels were now functionally extinct, which means the existing population can not reproduce fast enough.

Hillman told Checkpoint they were once home to sea life like snapper and scallops.

"They increase biodiversity just by increasing this habitat that other things can live on, that's the shells.

"But also, around as well, so you get things like small fish."

She said the shells also influenced how nutrients can travel through the sea.

"The movement of nutrients, oxygen, ammonium things like that...are really important for our global cycles."

So to help bring back the marine life that once thrived along the sea bed, Hillman and a team of scientists are trying to mimic the role once played by the dense mussel beds.

They will be made from crushed up recycled green-lip mussel shells leftover from farms, that would otherwise be thrown into landfill.

It is estimated about 35,000 tonnes of mussel shells are thrown away every year, costing more than $5 million.

"[We'll be] taking that, making it into this concrete, we're calling it concrete but it's completely natural, then putting it back into the sea.

"[It's] to create this circular economy, that then revives the sea."

The team is planning on planting them in six spots across the Hauraki Gulf, to help give struggling fisheries a second chance.

With teeming fisheries, they hoped it will attract local and international tourists.

Taylor Kielczewski, one of the students working on the project, said in the trial run, they had seen results as early as three months.

"The first experiment we will be running is on scallop predation, we'll be putting juvenile scallops in the mimic area and also the bare sediment to see where they'll survive longer."

It is part of restoring an ecosystem that critics say has taken a hammering from bottom trawling and dredging.

Auckland University marine science Professor Simon Thrush said if Aotearoa continued to fish this way, the health of our oceans will continue to drop.

"If we keep going as we currently do, then certainly we maintain degraded habitats, that have already been impacted by trawling.

"It is problematic because the ocean does a lot for us."

But Thrush said if some commercial fishing methods were to be banned, alternatives needed to be properly thought out.

"There's massive opportunities for technological innovation; there's massive opportunities for thinking about how we manage and understand the sea floor by looking at it in more detail.

"[Also] having meaningful maps of what the sea floor looks like."

The University of Auckland mussels research received $1 million in funding from the Ministry of Business, Innovation and Employment for the next three years.