Situated 10 minutes drive along the waterfront from Auckland’s CBD is Ōkahu Bay. Looking out across the Waitematā towards Rangitoto there was once a carpet of kūtai / mussels forming extensive reefs in the Rangitoto channel. Working in partnership with Ngāti Whātua Ōrākei, the Revive Our Gulf project is working to establish kūtai beds and restore the mauri / life force of Ōkahu Bay.
For Ngāti Whātua Ōrākei, this work has been multigenerational, and follows a vision for Ōkahu Bay laid down almost 10-years ago in the Ngāti Whātua Ōrākei long-term ecological restoration plan:
“Waters fit to swim in at all times, with thriving marine eco-systems that provide sustainable kaimoana resources to a Ngāti Whātua Ōrākei community who have strong daily presence in and on the bay as users and kaitiaki”.Ngāti Whātua Ōrākei long-term ecological restoration plan (Kahui-McConnell 2012)
We hope to see Ōkahu Bay become a ‘living laboratory’ where others can come and learn about kūtai reef restoration and help to turn our big blue backyard back into a place that is once again filled with abundance.
Restoring the kūtai / mussel reefs of The Hauraki Gulf / Tīkapa Moana/Te Moananui-a-Toi.
Kūtai/mussels improve water quality As filter feeders, kūtai/ mussels are the ‘kidneys of the sea’ removing heavy metals, harmful bacteria, clearing the water and stabilising the seafloor. Equipped with a powerful pump, a mussel can filter vast…Find out more
Frequently Asked Questions
Can people harvest and eat these kūtai?
No, please don’t! Even if you happen to be uri o Ngāti Whātua Ōrākei. You’ll wreck our experiment and chances are you’ll get really, really sick. Kūtai accumulated heavy metals, contaminants and bacteria in their flesh and Ōkahu Bay frequently is on the Safeswim high-risk list. Our hope is that our grandchildren’s grandchildren’s grandchildren will one-day have tasty, edible, safe kaimoana from the Waitematā.
What is known about the historic beds in Ōkahu Bay?
Ōkahu Bay was once an important source of kai moana for Ngāti Whātua Ōrākei, with large shellfish beds of pipi and tuangi / cockles. Historical records from mussel dredging show that there were dense beds of green-lipped mussels in the Rangitoto channel and other places in the Waitematā. It’s not clear how close to the Ōkahu Bay shoreline these beds came, although we have found some large kūtai shells in and around the area we are working. All up, over 500 sq.km of kūtai reefs were dredge fished from the inner Hauraki Gulf between 1910 – 1965.
Why haven't the beds recovered on their own?
Generations upon generations of kūtai went into forming the reefs. Fishers in the day recall the kūtai coming up like ‘rolls of carpet’. Marine scientists believe this fundamentally damaged the habitat, removing structure critical to the settlement of kūtai larvae / spat like filamentous algae, hydroids and hard shell surfaces. Sedimentation adds to the challenge, where poor land use practices have resulted in the loss of filtering wetlands and deforestation allowing large volumes of sediment to flow into the Gulf, making the water more turbid and the seabed conditions more muddy.
Despite shellfish beds being one of the most threatened marine habitats on Earth, there is still a lot to learn about shellfish bed ecology. Our subtidal, soft-sediment kūtai (Perna canaliculus), a species unique to Aotearoa / New Zealand, present some specific challenges, with different habitat needs across its lifecycle when compared to well studied shellfish such as oysters.
Why is a shell-base being trialed at Ōkahu Bay?
Kūtai are quite hardy and can handle a moderate amount of sediment suspended in the water. However, they don’t like being buried in it. The shell hash base used in Ōkahu Bay (50m x 50m and approx. 30-50 cm high) will be used in a large-scale test to compare survival of kūtai placed on a shell vs soft sediment. We expect the shell to improve survival and encourage recruitment by lifting the kūtai out of the muck and providing an attachment substrate for juvenile mussels and other marine life.
Will this project make a difference to water quality and biodiversity in Ōkahu Bay?
A single adult kūtai can filter between 150–350 litres of seawater per day. Assuming each of our six plots has around 700,000 mussels that’s about 630+ million litres of filtration per day! It sounds big, but let’s not get too excited, it’s a drop in a bucket considering the volume of water in Ōkahu Bay (and tidal currents etc). However, we will be keeping an eye out for any localised improvements in turbidity across the beds. Biodiversity improvement should be more apparent and we expect to see more species, like crabs and shrimps, juvenile fish and starfish to show up around the beds within 6–12 months.
Why is kelp part of the experiment?
The presence of kelp (in our case Ecklonia radiata) is known to reduce the accumulation of sediments, reduce predation by starfish, and there is also evidence that kūtai growth is enhanced. By monitoring the health, growth rates and biological communities, it is hoped that the study will provide evidence that kelp can help to establish kūtai reefs.
Reflections on the Australian Coastal Restoration Network Symposium: Strengthening Partnerships
Last week, a delegation from Revive Our Gulf headed to Townsville to participate in the Australian Coastal Restoration Network Symposium. This two-day conference brought together specialists in coastal restoration, from across Australia, fostering collaboration and knowledge exchange. A New Zealand delegation and the infusion of Māori tikanga into the conference gave the conference a distinctive... Read more »
26 May 2023
12 months on at Ōkahu Bay
This kaupapa is long-term and intergenerational, and for that reason, milestones defined simply by the passing of time can seem a little arbitrary. But, time itself can also be a marker of progress. Although it’s early days, we were excited to reach the 12-month anniversary of the Ōkahu Bay mussel reefs. I will confess to... Read more »
20 December 2022
Ōkahu Bay 6 months monitoring
Weather delayed our 6-month monitoring of Ōkahu Bay, but results now out… Beginning to see some difference in survival of the kūtai on shell (S1..S3) ???? vs, those on bare sediment (M1..M3) ????. A few small 11-arm starfish moving in but the water was clearer this time. Visit the Ōkahu Bay project page
25 August 2022
Photogrammetry reveals Ōkahu Bay kūtai beds in stunning detail
You could be forgiven for thinking that the kūtai / green-lipped mussels have been hard at work clearing the murky waters of Ōkahu Bay. Unfortunately, we would need square kilometers of kūtai beds to get the water this clear! These images were stitched together from lots of smaller, close-up photos to form a composite image... Read more »
23 May 2022
Ōkahu Bay three month monitoring results
It's been 3-months since we deployed 60 tonnes of kūtai into Ōkahu Bay. Here's the results of the 3-month monitoring that we recently carried out.
8 March 2022
60 tonnes of kūtai for Ōkahu Bay
Today we finish the job of depositing 60 tonnes of mussels / kūtai into Ōkahu Bay. Over the past two weeks our friends at NIML/Sanford have made three trips across from the Eastern Firth of Thames, bringing 20 tonnes of kūtai on each trip.
30 November 2021