Credit: Dave Allen

Posted on 14 September 2020

Early signs of success at mussel ‘restoration stations’

Commercial mussel lines are great at catching mussel spat, but are predominantly made of plastic. The Awhi Mai Awhi Atu project, led by Associate Professor Kura Paul-Burke (University of Waikato), is investigating the feasibility of using natural fibre lines to help restore kuku/mussel beds in Ōhiwa Harbour.

In 2007 there were 112 million baby kuku in a continuous 2km reef – by 2019 there were less than 80,000 in the entire harbour. Kuku, also called kutai, are a taonga (treasured) species for the local iwi, and crucial to the health of this ecosystem. 

Knowledge sharing 

Last week the research team deployed the lines, accompanied by Whaea Roka Ngarimu-Cameron and her students who helped weave the lines at a wānanga in August. Roka is a renowned weaving expert who has been awarded a Queen’s Service Medal for her services to Māori and the Arts, and we are honoured she has shared her mātauranga and expertise.

“These are the ‘second generation’ of lines – last year we deployed lines made from either harakeke, tī kouka or kiekie to check how well the spat would attach to each. The tī kouka lasted the longest, up to 5 months. This year’s lines are thicker and bushier to hopefully attach even more kuku, and different designs and compositions to see which lasts longest as well as the highest yield,” says Kura.

“It’s lovely to use a traditional resource in a new way,” says Roka, who is using her mātauranga to overcome the material science challenges.

"Last year’s lines eventually broke where they were attached to the buoys, so this year each line has a core of pirita for strength with either tī kouka, pīngao or neinei woven around it. I’m am very interested to see how the kuku like pīngao and neinei – and how long they last! Our ancestors said that tī kouka was the strongest, but they may not have used the others for this kind of hard-wearing use despite them being hardy plants. Pīngao was precious for her beautiful golden colour so only used for tukutuku and prized kete.”

Restoration stations 

As the kuku grow, they weigh down the lines. 

“When we checked last year’s lines, we couldn’t see them and thought they’d gone adrift,” says Kura. “Then we realised they were so heavy that they were totally submerged! There were 20,000 kuku per line, that’s about 50kg. The new bushier lines should be even better. 

The lines – with their kuku – eventually sink to the bottom and biodegrade, where the hope is that the kuku attach to the harbour floor as the foundation for a new bed. Kuku naturally grow together in clumps “as a whānau”, so the fact they fall together on the line is important. The project has set up of these ‘restoration stations’. 

A couple of weeks ago, the research team discovered early signs of success – three early-stage kuku beds, all near the stations where the first-generation lines were deployed this time last year. 

Zero waste, zero impact 

The lines are woven from pirita plus either  kouka bio-waste (leaves that have naturally fallen from the tree), pīngao or neinei. They eventually biodegrade into the water column, reducing microplastic pollution in the harbour, in kaimoana and in ourselves. 

About Ōhiwa Harbour 

Three of the four kuku beds in the harbour have disappeared in the last 10 years, affecting the harbour’s kaimoana (seafood), mahinga kai (cultivation) and mauri (vital essence), and reducing the ability of mana whenua to express manaakitanga (expression of respect and hospitality to visitors through provision of kaimoana). 

The exact causes of this ecosystem degradation are not yet fully understood. 

The harbour has been affected by human activities, and initially we suspected overharvesting for kaimoana was the main problem... but there was a rāhui in place for 8 years and in that time the number of pātangaroa [sea stars] exploded, and they love eating kuku. We don’t yet know why there’s been such a dramatic increase, or what all of the ecosystem impacts are, says Kura. 

 

Notes to editors

About the Sustainable Seas National Science Challenge – The vision of Sustainable Seas is for Aotearoa New Zealand to have healthy marine ecosystems that provide value for all New Zealanders. It brings together scientists, social scientists, economists, and experts in mātauranga Māori and policy. It is funded by MBIE and hosted by NIWA. 

About the National Science Challenges – Sustainable Seas is one of 11 National Science Challenges. These align and focus Aotearoa New Zealand’s research on large and complex issues, bringing together scientists and experts from different organisations and across disciplines to achieve a common goal.

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