Te Wero Nui

Combatting Caulerpa

Exotic Caulerpa, an invasive seaweed species, has been discovered in the North Channel, northwest Te Kawau Tūmaro ō Toi | Kawau Island.

Ngāti Manuhiri Settlement Trust, NIWA and Biosecurity New Zealand are working together to contain and remove the patches of Caulerpa in our rohe, read on to see how you can help.

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Te Wero Nui
Combatting exotic Caulerpa

Exotic Caulerpa is an invasive seaweed that colonises the seabed by forming large dense mats, killing our native seaweeds that many of our kaimoana, like snapper and crayfish, feed off.

It was first discovered in New Zealand in Blind Bay, Aotea in 2021 and most recently discovered in our rohe near Te Kawau Tūmaro ō Toi | Kawau Island in July 2023.

Exotic Caulerpa is easy to spread and hard to remove. A small fragment of the plant caught up in netting or on an anchor and released in another location is more than enough to help this invasive plant spread further.

That's why we're calling it 'Te Wero Nui' - it's a big challenge for us to tackle and get under control but it's important we move quickly. Our approach is remove, reduce, eliminate and that's what we've been doing since caulerpa was discovered in our waters in July 2023.

If you find caulerpa attached to your fishing or boating gear, do not return it to the ocean, bag it, record the location, report it, and take it home to dispose of in your home bin or compost.

Sightings can be reported through 0800 80 99 66 or by completing the online reporting form at report.mpi.govt.nz

What is Caulerpa?

Caulerpa is a seaweed that grows below the tidelines on hard, rocky surfaces and in sandy areas. It can grow up to 40 metres deep, forming dense mats with extensive root systems, suffocating native seaweeds, seagrasses and marine fauna.

They have green fronds up to 10 centimetres long in the shape of oar blades that rise from long runners or roots.

It's able to grow quickly and form large dense mats across the seabed which chokes other plants that our marine life depend on. This can displace fisheries and shellfish resources, and threaten biodiversity.

Caulerpa has been seen growing on scallops (pictured right) and dog cockle beds and while no formal research has been completed on the impacts of Caulerpa in New Zealand, the assumption is it will negatively impact these species.

It can reproduce from a small fragment and is often picked up by fishing gear or boat anchors which helps spread it to other areas. It is difficult to remove properly and should only be attempted by trained divers.

Two new types of non-indigenous algae were discovered in mid-2021 in Aotea, identified by NIWA researchers as Caulerpa brachypus and Caulerpa parvifolia.

Both types were given the status of Unwanted Organisms under the Biosecurity Act in September 2021 and are called exotic caulerpa to distinguish them from our native seaweeds.

Aotearoa New Zealand has a number of native Caulerpa that occur in similar habitats to exotic Caulerpa, these native Caulerpa could be impacted if exotic Caulerpa continues to spread.

What can you do?

Our best tool against exotic Caulerpa is awareness, familiarise yourself with what it looks like and share this knowledge with your friends and whānau.

Check your fishing and boating equipment for any pieces of Caulerpa that may have been caught up. If it looks like Caulerpa, treat it as Caulerpa, bag it, record the location, and take it home to dispose of it in the bin or compost, report the location to MPI

If you see Caulerpa in the water, do not try to remove it as this can help it spread further. Take a photo if possible, record and report the location to MPI.

If you're a diver willing to train in Caulerpa removal, please get in touch through the form below.

If you think you've spotted Caulerpa, do not attempt to remove it, note the location, take a photo and report it to Biosecurity New Zealand on 0800 80 99 66 or complete the online reporting form at report.mpi.govt.nz

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Removal methods

Our approach is remove, reduce, eliminate Caulerpa.

While eradication is our ultimate goal, our immediate focus is on removal and containment of the current outbreak.

Ngāti Manuhiri Settlement Trust, Biosecurity New Zealand/MPI, NIWA and experts from California USA, are working together to contain and remove the patches of Caulerpa. This involves meeting to strategise and develop an effective plan of action, a roadshow to raise awareness, and taking to the moana to initiate the cleanup process.

We will continue to survey the infestation and consider a range of options considered for removal, such as hand removal, salt, or chlorine treatments. Ngāti Manuhiri Settlement Trust kaitiaki will be involved in the process to ensure mātauranga Māori is utilised and protected.