On this page
- Eradication of exotice caulerpa is unlikely
- Technical advice on the response to the discovery of exotic caulerpa (February 2022)
- Technical advice on a long-term management strategy for exotic caulerpa (February 2024)
- Technical advice on suction dredge treatment (July 2023)
- Aotea exotic caulerpa removal trial (February 2024)
- Impact of exotic caulerpa on native species – Phase 1 interim report (April 2023)
- Impact of exotic caulerpa on native species – Phase 2 report (December 2023)
Eradication of exotic caulerpa is unlikely
From the outset of our response to exotic caulerpa in mid-2021, the scientific advice and international experience has told us that eradication (full and permanent removal) of this pest is highly unlikely given the:
- large size of the incursion in New Zealand
- the lack of any control tool internationally that would work at this scale.
Despite this, experts have continued to explore and trial options for killing the seaweed in the hope of finding techniques that could help remove, for example, new and small outbreaks or knock back larger populations to try to reduce further spread.
Technical advice on the response to the discovery of exotic caulerpa (February 2022)
Response actions and decisions are informed by scientific advice. Since the discovery of exotic caulerpa in New Zealand in 2021, groups of international technical and scientific advisors with expertise in marine algae, control methods and Mātauranga Māori, have convened to advise on the situation and recommended actions.
The first Technical Advisory Group (TAG) met in December 2021 to provide advice on the incursion in New Zealand and the most appropriate response to its discovery.
The group concluded that:
- the scale of the New Zealand incursion is beyond that at which successful eradication has ever been achieved internationally
- eradication within each infected area is not possible with the current set of tools available
- the most appropriate course would be to aim for suppression and containment, with a long-term management plan required to limit further spread.
Technical advisory report: Caulerpa Great Barrier Island 2021 response [PDF, 951 KB]
Technical advice on a long-term management strategy for exotic caulerpa (February 2024)
A further group of technical advisors met in July 2023 to advise on a long-term strategy for exotic caulerpa management. While recognising strong community desires to eradicate exotic caulerpa, the group reports that this is not currently a realistic objective. It set 6 objectives for future management.
- Prevent establishment outside the current infested region.
- Slow the spread within the existing infested areas.
- Protect and restore the mauri of high-value affected sites where it can’t be eliminated.
- Minimise impacts on the environment, communities and customary practices.
- Increase understanding of the behaviour and impacts of exotic caulerpa.
- Ensure investment in exotic caulerpa management and marine biosecurity enables the development of better tools and capability for more effective marine responses.
Exotic caulerpa strategic Technical Advisory Group report [PDF, 12 MB]
Technical advice on suction dredge treatment (July 2023)
In June 2023, an advisory group gathered to advise on the use of diver-controlled suction dredging to remove exotic caulerpa.
The group recommended an immediate scientific trial to provide vital information on the method’s potential in our unique environmental conditions and the remote locations of our caulerpa infestations.
Exotic caulerpa suction dredge Technical Advisory Group report [PDF, 933 KB]
Aotea exotic caulerpa removal trial (February 2024)
This proof-of-concept trial set out to evaluate the use of diver-controlled suction dredging for local elimination of exotic caulerpa.
In this trial, NIWA tested suction dredging alone and in combination with secondary treatments of chlorine dosing and benthic matting at 3 locations in Tryphena Harbour, Great Barrier Island. The 3 sites were monitored immediately after the treatment and one and 2 months after.
Aotea caulerpa removal trial: suction dredging, benthic covers, and chlorine dosing [PDF, 7.2 MB]
Impact of exotic caulerpa on native species – Phase 1 interim report (April 2023)
Biosecurity New Zealand commissioned NIWA to assess the impacts of exotic caulerpa on the ecosystem and taonga species at Aotea Great Barrier Island.
In a multi-year study, NIWA monitored 18 permanent sites in the 3 affected bays at the island – Blind Bay, Tryphena Harbour, and Whangaparapara Harbour.
They looked at any effects on native species, as well as how the caulerpa itself was affected by wave energy and light availability, including storms.
In the interim report, observations suggested that exotic caulerpa might be having a negative impact on the condition and population dynamics of taonga species. However, the report states that further sampling and analysis is required before the extent of any impacts on most of the habitats would be known.
Impact of exotic Caulerpa on native species at Aotea/Great Barrier Island – Phase 1 [PDF, 1.9 MB]
Impact of exotic caulerpa on native species – Phase 2 report (December 2023)
NIWA returned to the 18 permanent sites in June 2023 and found that exotic caulerpa cover had increased significantly at shallow sites in Okupe/Blind Bay but was variable at deeper sites. As in Phase 1, taonga species kina and tipa (scallops) appeared to have been negatively affected in areas with dense exotic caulerpa.
However, this research is part of an ongoing programme and as such, this is an interim report. It finds that continued monitoring is required to allow robust conclusions on the role exotic caulerpa is having on the functioning and population dynamics of target species and habitats.
Impact of exotic caulerpa on native species at Aotea Great Barrier Island field report (trip 2) [PDF, 3.8 MB]
