Exotic Caulerpa, an invasive seaweed, has been discovered in New Zealand waters and poses a significant threat to our marine and coastal environment.
Exotic Caulerpa grows rapidly, expanding both underwater (up to 40m deep) and in intertidal zones. It can grow up to 3 centimeters in length each day, forming dense mats that smother and displace native seaweeds and marine life. It spreads easily by fragmentation which makes it difficult to control and presents challenges for removal efforts.
Overseas studies of similar species have shown a 50% reduction in biomass and a 30% reduction in biodiversity in 6 years where exotic Caulerpa is allowed to take over. It’s a threat to our marine taonga, our shellfish and to our way of life.
Exotic Caulerpa has been seen growing on scallops and dog cockle beds and is a serious threat to our work in kūtai / mussel reef restoration.
What we’re doing
Revive Our Gulf is collaborating with our Tangata Whenua partners, Auckland Council, and Biosecurity New Zealand, to increase surveillance for exotic Caulpera in the Hauraki Gulf. We are working to accelerate our marine monitoring programmes to build capability and capacity in surveillance and monitoring and supporting Te Wero Nui, the community convening response of Ngāti Manuhiri.
Restoring the kūtai / mussel reefs of The Hauraki Gulf / Tīkapa Moana/Te Moananui-a-Toi.
What you can do
Keep your boat & gear clean Exotic Caulerpa can be easily spread as small pieces on vessels and marine equipment. Before moving locations, inspect your anchor, chain, and gear for any seaweed. Report any findings, and bag and bin at home.
More info (MPI)
Respect the closures Familiarise yourself with the Closed Area Notices (CANs) and rāhui in place at various locations. Know where these are and respect the rules. Don’t anchor or fish.
More info (MPI)
Report it if you see it Keep an eye out for exotic Caulerpa species and report suspected sightings to MPI/Biosecurity NZ. Take a photo, if possible, and note the location.
Learn to spot exotic Caulerpa (Youtube MPI)
How to report exotic Caulerpa (MPI).
Tell others about it Tell 5 people about exotic Caulerpa and ask them to tell 5 more. Our best chance is early detection so the more people aware and able to spot new infestations the better.
Frequently Asked Questions
What is exotic Caulerpa
Caulerpa is a family of seaweeds. In Aotearoa New Zealand we have native species of Caulerpa, but two pest species, Caulerpa brachypus and Caulerpa parvifolia are new arrivals and a serious problem. They are considered ‘Unwanted Organisms’ under the Biosecurity Act September 2021, and hence they’re being referred to as exotic caulerpa to set them apart from our native seaweeds. The classification as an Unwanted Organism means that special permission is needed to handle and remove them.
Where has it been found?
Exotic Caulpera was first discovered in New Zealand in Blind Bay, Aotea in 2021 and has been since discovered in areas of the Hauraki Gulf and Bay of Islands. Refer to Biosecurity NZ for latest information on the location of exotic Caulerpa.
Where is it from, and how did it get here?
These exotic Caulerpa species are native to the Indo-Pacific region, ranging from Africa to Australia, the Pacific Islands, and southern Japan. They most likely arrived as a stowaway on a boat anchor or anchor chain.
What does it look like?
Caulerpa brachypus and Caulerpa parvifolia are closely related and appear identical. They have green fronds up to 10 centimeters long in the shape of oar blades that rise from long runners or roots known as stolons. They can be found growing below the tideline at between 2 meters and 30 meters on both hard surfaces and in sandy areas. When established, exotic Caulerpa can cover large areas of the seafloor in dense mats.
Why is it such a threat to our marine ecoystem?
Exotic Caulerpa can grow quickly and form large dense mats across the seafloor which smother photosynthesising plants and suffocate filter feeding animals that other marine life depend on. It is displacing fisheries resources, and threaten biodiversity.
Experience in the Mediterranean with Caulerpa taxifolia has seen a 30% reduction in biodiversity and a 50% reduction in fish biomass in 6 years. This sort of damage would be devastating for the Hauraki Gulf, which is already under significant pressure. The area at risk is currently considered to be the top of the North Island down to the Bay of Plenty.
What is being done to remove it?
Because exotic Caulerpa spreads by fragmentation (it can spread by seed too!) you have to be really careful when removing it. Overseas experience has been that small areas can be treated with benthic mats. Chlorine pumped under the mat, or in the form of pool tablets, is sometime used to accelerate die off. Larger infestations will need to be treated with vacuum dredging. A vacuum dredging trial is currently underway in Aotea Great Barrier and up at Omakiwi Bay Bay of Islands.
 Harmelin, Mireille, et al. Impact of Caulerpa taxifolia on Mediterranean fish assemblages: a six year study. Proceedings of the workshop on Invasive Caulerpa species in the Mediterranean. UNEP, January 1999.
Exotic Caulerpa surveillance – The Noises islands – Aug 2023
In the picturesque last days of winter around The Noises, Revive Our Gulf and Coast & Catchment, conducted video surveys around the Island group. Our goal? To check for the presence of two invasive Caulerpa species: Caulerpa brachypus and Caulerpa parvifolia. The marine habitats surrounding The Noises are diverse – including rocky reefs, kelp forests,… Read more »
1 September 2023
Our letter to Ministers about Exotic Caulpera
Revive Our Gulf partners recently wrote to the Ministers of Biosecurity and Conservation to express our extreme concern about the threat posed by exotic Caulerpa to Aotearoa / New Zealand’s coastal waters. A response from the Minister of Biosecurity, Hon Damien O’Connor, was received in early June.
16 May 2023