Mussel power: Seven million kūtai deployed to help restore Hauraki Gulf ecosystem

The harvest of kūtai which will be placed in Kawau Bay. Photo / Ngāti Manuhiri Settlement Trust, Delma O

Seven million kūtai (green-lipped mussels) will be deployed into the Hauraki Gulf/Te Moananui-ā-Toi/Tīkapa Moana in a bid to reverse the decades-long impacts of destructive fishing practices, invasive species, climate change, and acidifying waters.

Ngāti Manuhiri Settlement Trust, as a partner of the Revive Our Gulf project, will place millions of kūtai in Kawau Bay on Monday, July 29.

“Kūtai are absolutely crucial to maintaining the health of our wai but our once abundant kūtai populations have been severely depleted by human activity and climate change,” trust chief executive, Nicola MacDonald said.

“By re-establishing these kūtai reefs we are taking solid and decisive action to reverse the human impacts on the Gulf, and give our wai a fighting chance to ensure it is stable enough to support us now and into the future.”

A boat harvesting kūtai. Photo / Ngāti Manuhiri Settlement Trust

Kūtai are ecosystem engineers, providing food, shelter, and protection for diverse species as well as filtering impurities from the seawater.

“In the 1950s and 1960s the extensive kūtai reefs of Te Moananui-ā-Toi were commercially dredged to the point of collapse. Despite the advent of mussel farming, wild mussels never returned in large numbers,” Revive our Gulf programme director, Katina Conomos, said.

“Healthy shellfish in the Hauraki Gulf are key to healthy marine ecosystems. We need to bring them back.

“We are developing knowledge for how to restore kūtai populations in Te Moananui-ā-Toi at scale. Ngāti Manuhiri Settlement Trust is a very committed partner to this kaupapa, and their bold leadership is essential to this mission.”

“Originally the spat, or baby kūtai, are collected from Te Oneroa-a-Tōhe (Ninety Mile Beach) and then grown to size on a mussel farm in Coromandel, and then brought here by barge.“

This deployment is the second conducted in partnership with the trust, and is part of a wider project to develop knowledge around the restoration of the kūtai reefs throughout Te Moananui-ā-Toi/Hauraki Gulf.

“One of the other problems we are facing across the Gulf is the spread of the invasive seaweed exotic caulerpa,” MacDonald said.

“Some of the techniques used to remove exotic caulerpa involve chlorine and benthic liners to smother it; however this can have a brutal scorching effect on the seabed and upset the conditions needed for our native plants and fish stocks to thrive.

“Kūtai can help to filter the wai and restore it to ideal conditions for our marine life to flourish, particularly kōura (crayfish) and tāmure (snapper).”

One of Revive Our Gulf’s core partners is the Nature Conservancy and its country director for Aotearoa, Abbie Reynolds, says the kūtai restoration project is an internationally recognised example of successful indigenous partnership.

“The way that this project works hand in hand with mana whenua is particularly exciting, upholding the mana of all involved, and we are honoured to be a part of this important conservation work with the wider benefits that it entails.”

University of Auckland Institute of Marine Science lecturer, Dr Jen Hillman, who is the science lead for Revive Our Gulf, describes this as cutting-edge marine research.

“We are learning as we go and it’s a huge ongoing effort. This scale of work that Ngāti Manuhiri are driving is a world first in restoring these types of shellfish.”