In July 2024, in partnership with the Ngāti Manuhiri Settlement Trust, we deployed seven million kūtai (green-lipped mussels) across six sites at Martins Bay, and another two sites North-West of Motuora Island.
Having already conducted several surveys of the deployments this year, a team of SCUBA divers were back in the water in August to undertake our one-year check in on the kūtai and piece together some of the insights we’re able to gather from this kaupapa.
Ngāti Manuhiri and Revive Our Gulf kaimahi operating our ROV.
What did we find earlier this year?
SCUBA divers were in the water in February to do the first formal check-in on the kūtai, seven months on from our initial deployment. What they found at the three sites they visited were potential signs of stress amongst the kūtai, impacting their growth and density.
As a result, our team followed up with ROV visits to each of the sites, collecting video footage of the seafloor to get a first-hand look at what’s going on and pull together a more fulsome view of the entire deployment. The surviving kūtai were showing clear signs of stress: despite being considered resilient ecosystem engineers there comes a point where even the mighty kūtai struggles with the combinations of stressors that persist across the Hauraki Gulf.
The changes in these kūtai highlights the complexity of our seafloor environments, not only at these sites but across the entire Hauraki Gulf. It will be difficult to pinpoint a single tipping point for these kūtai – rather, it is likely to be a combination of things that have impacted these deployments: water temperatures, food quality, and extreme weather causing sediment and untreated sewage overflows all compounding to exacerbate the already stressful environment.
Sponges and ascidians growing on the kūtai at Martins Bay.
One year on, has anything changed?
Our August check in confirmed that, while they were still putting up a fight earlier this year, many of the kūtai were beyond recovery. The number of empty shells had significantly increased since our earlier monitoring, with thick layers of sediment settling on some of the kūtai.
While there may not be many living kūtai left, there are still plenty of signs of life: sponges, ascidians, whelks and chitons were all spotted in and amongst the shells. A school of jack mackerel were seen swimming near the bed at Motuora Island. Several Octopus dens were spotted amongst the empty kūtai shells, with two Wheke (Gibbs Octopus) seen during our observations – no doubt drawn to the area due to a sudden abundance of kai (food), the likes of which haven’t been seen in over 80 years.
A Gibbs Octopus in its den and a white-striped anemone (Anthothoe albocincta) at Motuora.
So what’s next for these kūtai?
Our resource consents require us to continue monitoring these deployments, even when experiments don’t work out the way we want – and there’s still so much we can learn from what we see happening below the surface.
There are still live kūtai at both Martins Bay and Motuora Island that are useful to be monitored. There is also a significant amount of learning we can do on the ecological benefits and value of shell beds, as well as looking at the whole life cycle of kūtai and identifying at which stage intervention has the most profound impact.
How differently each site responds to these projects at this early stage demonstrates just how difficult restoration work can be. Even areas that are geographically not considered to be far apart are responding in unique ways, each attracting different species and predators, with different rates of mortality and kūtai growth.
Every time we observe these kūtai, it helps us get one step closer to figuring out the ideal combination of density and location for a deployment by showing us what we’re getting right, as well as what areas we need to dive deeper into so we can bring back the once extensive kūtai beds that carpeted the floor of the Hauraki Gulf.