In August 2024, we partnered with Ngāi Tai ki Tāmaki to deploy approximately 56 tonnes of kūtai (green-lipped mussels) back into the Hauraki Gulf in an effort to support the re-establishment of soft sediment kūtai beds.
Having already completed our six-month observation in February 2025, a team of SCUBA divers were back in the water in August to undertake our one-year check in on the kūtai and start to build a picture of how each of the sites are doing.
There were mixed results, which isn’t always a bad thing – particularly for this deployment. While our overarching goal is to re-establish self-generating kūtai reefs, this kaupapa with Ngāi Tai ki Tāmaki has an additional aim: to test how suitable different sites are for kūtai restoration.
A total of fourteen deposits, each with approximately 4 tonnes of kūtai, were placed across three sites: the Tāmaki Strait (Mid-Tāmaki), Te Pounui-o-Peretū (Ponui) and Rotoroa Island (Rotoroa). Four plots were visited for our one-year check-in: two at Mid-Tāmaki and one each at Ponui and Rotoroa, with further monitoring taking place in October and December 2025.
Ngāi Tai ki Tāmaki and Revive Our Gulf kaimahi monitoring sites in October and December 2025.
How are the kūtai doing?
This varies across the beds we visited. At Ponui, while the kūtai have largely survived their first year, they haven’t grown very much. It’s a similar story at Rotoroa, where there’s been a slightly higher rate of mortality than at Ponui, but growth in the size of the kūtai hasn’t been as evident.
Where we’ve seen the most change is at the Mid-Tāmaki beds. While there has been a more noticeable level of mortality, it isn’t at a level we’re concerned about at this stage – and the positive news is the kūtai that have survived are showing high growth rates, between 5-9 cm on average!
Despite the difference in survival rates between the beds, all four that were visited in August now have a similar density of kūtai thanks to the varying sizes of the original deployments.
White encrusting sponge growing on the kūtai at the Mid-Tāmaki beds.
Has there been any change in the surrounding environment?
This also varies depending on the sites we looked at. The Ponui bed showed little signs of epibiota (organisms that live on the surface of another) or predators, while the Rotoroa and Mid-Tāmaki beds showed various combinations of species at the sites.
At the Rotora bed, there were several large sea cucumbers, various sponges, ascidians and small gastropods. At the Mid-Tāmaki plots, there were various sponges (Dysidea sp), mussel’s beard hydroid (Amphisbetia spp) and seaweed (Carpophyllum flexuosum). A common sight at both beds were a white encrusting sponge growing on kūtai shells, as were various species of triplefin fish.
There were also several predators and pests seen throughout this round of monitoring, although their density was similar to pre-deployment levels. Mediterranean fan worms (Sabella spallanzani) were located at all sites, while low levels of Eleven-armed starfish (Coscinasterias muricata) and clubbed tunicates (Styela clava) were seen in varying combinations across the Rotoroa and Mid-Tāmaki plots.
Mussel’s beard hydroid and Dysidea sp. sponge growing on the kūtai at the Mid-Tāmaki beds.
So what does this all mean?
We’re starting to get a good idea of the impact these deployments have had at each of the different sites – but even a year in, it’s still too early to tell what the impact will be. Around the world, we see that marine restoration efforts are most likely to settle into their more long-term patterns after at least two to three years and start generating some longitudinal data.
What’s encouraging is that we’re seeing different results and responses at each of the sites, which supports the aim of this kaupapa to test the suitability of different sites for kūtai restoration, meaning we’ll have lots of evidence to draw from to inform future restoration mahi.
What’s next for these kūtai?
Ongoing monitoring will be crucial to help build long term data sets, seeing how trends play out, and observing how the kūtai grow and impact their surrounding environments.
Our next formal observation with divers is due in August 2026, at the 24 month mark for this deployment. In addition, we have just completed some additional monitoring with Ngāi Tai ki Tāmaki using our ROV, which we’ll continue to do periodically as it helps to build a more comprehensive picture of each of the sites.