8 October 2026
Kia ora tatou. In this issue:
Research provides growing evidence base
Exotic caulerpa tool development wins award
Video and briefing for sport fishers
Next Revive Our Gulf online Community Forum
This year’s research report summaries
Next issue: We'll report on a review of Controlled Areas.
Research provides growing evidence base
The 2025/26 exotic caulerpa research programme has improved the understanding of the pest’s spread, biology, and impacts, providing a growing evidence base for long-term management decisions.
Research is one of five key workstreams in the Exotic Caulerpa National Strategy agreed by partners.
Most of this year’s research projects were done by New Zealand-based providers Earth Sciences New Zealand, Cawthron Institute and University of Auckland, along with tool developers Flying Fish Technologies, Advanced Aquarium Technologies and Commercial Dive Specialists.
Taken together, the research indicates that because of fluctuations in biomass, exotic caulerpa is possibly not causing as significant long-term ecological impacts in New Zealand as initially thought. For example, researchers say there are no major direct effects on scallops at current low exotic caulerpa cover. However, juvenile snapper nursery habitat is at risk if exotic caulerpa invades seagrass.
Pictured above: New Zealand research shows that mature snapper feed on crustaceans and other creatures amongst exotic caulerpa (as pictured above), while young snapper avoid it.
The research includes evaluations of advanced surveillance and treatment tools that have been developed by New Zealand’s exotic caulerpa programme. These assessments highlight the challenges of achieving large-scale suppression or eradication of established exotic caulerpa infestations.
Also, this year’s research indicates that Caulerpa brachypus and Caulerpa parvifolia differ significantly in their ecology and potential risks, challenging assumptions that the species can be managed as a single pest. One main difference from the management perspective, for example, is Caulerpa parvifolia is more cold-tolerant.
Pictured above: A map showing the exotic caulerpa species at several locations. This is based on sampling by Earth Sciences New Zealand, Cawthron Institute and University of Auckland.
For more detailed summaries of 11 of the new research reports, see the last item of this email.
Exotic caulerpa tool development wins award
Commercial Dive Specialists won the Outstanding Initiative Award for the Rehabitat containment chamber, at the NZ Marina and Boatyard Conference in Tauranga on 24 September.
Rehabitat is a system that was developed with Biosecurity New Zealand co-funding to address exotic caulerpa.
Created by Brook McRae and his team, Rehabitat uses a containment chamber placed over an affected area of seabed. A controlled treatment neutralises the exotic caulerpa while containing the process and minimising disturbance to the surrounding environment.
The system has been developed through extensive prototyping and field trials and can be deployed in different sizes to respond to outbreaks at varying scales.
Commercial Dive Specialists has worked with Biosecurity New Zealand, iwi, regional councils and research organisations to develop and trial the technology. While initially designed to treat exotic caulerpa, the system also has potential applications within marinas.
Pictured above: Founder Brook McRae (right) and Alexandre Rissatto of Commercial Dive Specialists celebrate their Outstanding Initiative award.
View an interview with Brook McRae about the development of this tool.
Video and briefing for sport fishers
New Zealand’s 55 sport fishing clubs got a chance to view a new 1-minute marine biosecurity video featuring exotic caulerpa, during their national council’s AGM in Whitianga in mid September.
The video is one of two produced by the Protect Our Paradise programme for the fishing clubs to use during their pre-event briefings and on their social media. The Council’s own communications staff and the Tairua-Pauanui Sport Fishing Club helped with filming. These clubs have a total of 35,000 members between them.
The videos explain what recreational fishers need to do to avoid spreading marine pests. One video highlights the threat of exotic caulerpa and is for use from North Cape to East Cape, and the other video is more generic.
Jackie Bedford from Biosecurity New Zealand also updated the delegates on the Exotic Caulerpa programme and how fishers, as frequent visitors to coastal areas, can help with reporting sightings of bird flu.
Pictured above: Tim Evans, President of the Tairua-Pauanui Sport Fishing Club, pictured with Biosecurity New Zealand’s Jackie Bedford, organises some Protect Our Paradise collateral to spread the marine biosecurity message at his club.
Next Community Forum, Tuesday 27 October
The next online Exotic Caulerpa Community Forum hosted by Revive Our Gulf will be held on Tuesday 27 October, running from 1.30 to 3pm.
This forum is a space for Hauraki Gulf communities, iwi and agencies to come together, share information, ask questions, discuss progress and consider how national direction is translating into locally led surveillance, monitoring and removal efforts.
This could also be useful to people outside the Gulf who are interested in exotic caulerpa, as there are briefings from Biosecurity New Zealand and others.
This year’s research report summaries
Following is a short summary of 11 of the research outputs .
Understanding impacts on fisheries
Earth Sciences New Zealand (ESNZ)
Juvenile snapper nursery habitat at risk if exotic caulerpa invades seagrass
No major direct effects on scallops at current low exotic caulerpa cover.
Further research on impacts of exotic caulerpa on seagrass and scallop survival is needed.
Sexual reproduction
Cawthron Institute
High light levels trigger sexual reproduction and die‑offs.
Gametes (reproductive cells) develop into young algae within approximately 35 days.
Population dynamics
Cawthron Institute
Die‑offs are temporary; populations are rebounding - generally this is occurring on stable substrates like rock and reef.
Fragmentation dominates; anchors remain the key vector. Caulerpa brachypus is less widespread than Caulerpa parvifolia.
Genetic sequencing
ESNZ
Caulerpa brachypus in New Zealand is a unique gene variation; Caulerpa parvifolia matches the Australian one.
The two exotic caulerpa species can be reliably distinguished in the field. Globally, records are often misidentified.
Rocky reef impacts and population dynamics
University of Auckland
Offshore reefs show active spread of exotic caulerpa but low density on hard substrates. Patches vary by site in regard to growth and density.
Impacts are currently low but could increase once dense meadows form.
Students are continuing this work.
Fragmentation research
University of Auckland
Used lab-based experiments only on Caulerpa parvifolia
Fragments proved to be highly resilient, eg to cold and darkness, and they regenerate quickly after exposure.
In a simulation of boat anchor locker conditions, with no sediment, viability of fragments was 12–24 hours.
Surveillance strategy
ESNZ
A risk-based framework is used that combines habitat suitability, spread pathways (ocean currents and vessel movements), site value and surveillance history to prioritise where surveillance should occur.
It focuses surveillance on the highest-priority locations where exotic caulerpa is most likely to be present and where early detection would provide the greatest management benefit.
The framework integrates past detections and non-detections to estimate the current probability of presence and avoid duplicating effort in well-surveyed areas.
This report recommends using the most effective survey methods under suitable conditions, with diver surveys generally providing the greatest detection capability.
Novel large-scale surveillance tools
Flying Fish Technologies (FFT)
Underwater piloted gliders rapidly cover large areas; covering approximately 96.5 kilometres of transects and approximately 337,000 square metres of seabed in eight days, far exceeding what is done by divers working with remotely operated vehicles.
A machine‑learning based detection model achieved approximately 92 percent accuracy in simple habitats with high exotic caulerpa density or abundance, but weaker accuracy in coastal, turbid (stirred-up) or visually complex habitats.
The FFT AI model needs more training data for complex or turbid sites.
UV‑C impacts and marine macroalgae health index development
ESNZ
UV‑C causes exotic caulerpa to experience strong stress and biomass loss but requires repeated treatments.
Rhodolthis (red algae) and native caulerpa are also impacted by UV-C.
Shows promise for suppression in the right setting; not eradication.
Rehabitat (chlorine treatment) efficacy and impacts
Cawthron Institute
Chlorine treatment chambers reliably achieve target concentrations and are able to be maintained well.
Bleaching is observed in both undaria (invasive kelp) and exotic caulerpa, but complete death is uncertain. More time is needed to assess if there is any recovery after bleaching.
Non‑target macroalgae and macrofauna are also affected but recover within months; organisms in the sediment are largely unaffected.
UV‑C long‑term control
Advanced Aquarium Technologies (AAT)
UV‑C suppresses exotic caulerpa but resilience means variable field outcomes.
Non‑target impacts and scalability uncertainties remain.
The full research reports can be viewed on the MPI website - or use the QR code below.
Nāku noa, nā – The Exotic Caulerpa Programme team on behalf of the exotic caulerpa management partners.
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For more information about exotic caulerpa seaweeds in New Zealand visit the Ministry for Primary Industries Biosecurity New Zealand website.