EDITORIAL: Exotic Caulerpa incursion: A monumental failure in marine surveillance and biosecurity preparedness 

BARRY SCOTT (Editor)

First identified in Okupu/Blind Bay, on Aotea in June 2021(1)(2), then in the western bay of Ahuahu/Great Mercury Island a few months later(2), the invasive exotic caulerpa seaweed has now been found at Te Rāwhiti in the Bay of Islands(3). In all three cases the caulerpa was well established as ‘meadows’ of seaweed, suggesting it had been present at all three sites for a long period before detection. The first report was made by botanist, and Aotea local, Jack Warden while out fishing in a kayak in Okupu. He posted photographs of the unusual green alga on iNaturalist, where it was quickly identified by a caulerpa expert, Sergio Díaz-Martínez, in Mexico. Jack tagged a NIWA scientist in his post who notified Biosecurity New Zealand (BNZ) and arranged for samples to be collected from Blind Bay for identification. Analysis of those samples revealed that the species was Caulerpa brachypus. A second species that is equally invasive, C. parvifolia, was later found at some of the sites. Further surveillance by NIWA divers, under contract to Biosecurity New Zealand, identified further small patches of caulerpa in Tryphena and Whangaparapara harbours and then later a large infestation in the western bay of Ahuahu/Great Mercury. Controlled area notices (CANs) together with Rāhui were imposed at all four bays. 

CAULERPA THE ‘KILLER ALGA’

Variously described as ‘the killer alga’(4), the ‘foot and mouth disease’ of the ocean, and ‘kikuyu of the sea’, exotic caulerpa is one of the most serious invasive seaweeds in the world. It is its rapid and invasive nature that makes it such a serious threat to our marine environment. Caulerpa is a group of single celled, multi-nucleate (coenocytic), green macroalgae, comprised of a horizontal stolon (or rhizome) with erect green photosynthetic fronds, and colourless rhizoids that anchor the alga to both soft and hard seabed surfaces. Its ability to fragment allows for rapid clonal expansion and dispersal. However, there are marked differences among Caulerpa species in their ability to produce fragments and in the ability of the different tissue fragments to regrow. Nine native species of Caulerpa have been identified in New Zealand waters, but it is the exotic species that are problematic—a situation we are all familiar with for our land-based species, such as Clematis vitalba (Old Man’s Beard), which has become a serious problem weed, whereas the stunning white flowering native clematis, C. paniculata, is an integral and well adapted component of our native forests. The two Caulerpa species associated with the current incursion, C. brachypus and C. parvifolia, grow naturally in the warm waters of the Indo-Pacific region ranging from Africa to Australia, the Pacific Islands and southern Japan, but also now appear to thrive in the clear open waters of the bays and harbours of the north-east coast of the North Island. 

While Okupu was initially thought to be the index or primary site for the incursion, it is now more likely, given how well established the caulerpa is in Omakiwi Bay and the associated Te Rāwhiti channel, that the initial incursion was in the Bay of Islands, with fragments spreading from there by a vessel(s) plying the well-known ‘yachtie’ blue highways. Whole genome sequencing of samples of the two species from each of these sites should soon allow us to determine the probable initial site and the pathway of spread from there. 

FIRST RESPONSE: CONTROLLED AREA NOTICES, A PILOT AND PUBLIC ENGAGEMENT

Following the initial detection of caulerpa at Okupu in June 2021 and the placement of CANs at the infested sites, the first ‘on the ground’ response to test a method to control it was a small scale pilot mounted in December 2021 at Okupu(2). Two plots (2 x 12m2) were covered with rock salt and hessian mats to kill the caulerpa by osmotic shock. Subsequent monitoring revealed that the caulerpa, and most other organisms in the plots, were killed, but the caulerpa quickly re-established. Alarmingly, the patches in Tryphena and Whangaparapara harbours grew from 0.01 to 1840, and 10 to 1750m2, respectively, in the three-month period from the first surveys there in September 2021 to the time of the pilot in December 2021. No further attempts have been made by BNZ since then to control the growth and spread of these infestations on Aotea. 

A technical advisory group was set up in late 2021 to provide independent, expert and technical advice on methods/tools to manage caulerpa on Aotea. They reached the conclusion that with the tools available it would not be possible to eradicate caulerpa from the western bays of Aotea(5). No specific recommendations were made on how to control further spread, apart from the restrictions associated with the CAN, further research, and the implementation of a community ambassador programme. This operated over the summer of 2022/2023 to increase boatie awareness of caulerpa biosecurity risks. Disappointingly, no further removal/eradication methods were trialled on Aotea, despite the fact that successful eradication of exotic C. taxifolia, had been achieved in two lagoons in Southern California(6)(7), albeit in relatively small areas by comparison with the areas of infestation on Aotea. As of early 2022 these measured 1.5ha in Whangaparapara, 44ha in Blind Bay and 2.2ha in Tryphena. There is a feeling among many of us that BNZ gave up too easily and gave little consideration to the economic, social and environmental consequences of doing nothing. 

How California Dealt with it: Good surveillance, preparedness and a rapid response

Preventing the establishment of an exotic organism in any country is dependent on three key biosecurity elements:

• Good border controls and surveillance to detect the unwanted organism at an early stage before it can enter or soon after it has crossed the border,

• Good management plans in place to prepare for specific types of incursions, and

• Being able to mount a rapid response to the incursion. Ticking all three of these boxes is absolutely essential to prevent the establishment of such a highly invasive marine species as exotic caulerpa.

These good practice biosecurity measures are best exemplified by the successful eradication of two small incursions of C. taxifolia in two Southern Californian lagoons – Agua Hedionda Lagoon and Huntington Harbor – by the San Diego Regional Water Quality Control Board. Field containment and treatment by the Southern Californian Caulerpa Action Team (SCCAT)(6)(7) commenced within 17 days of detection, a response akin to that of an oil spill. For phase one of the eradication plan they placed tarpaulins over the seaweed then added hypochlorite pellets to release chlorine to kill it. This was then followed up with intensive surveillance and manual treatment by divers to remove all residual material from the site over a period of six years (2000-2006), and at a cost of US$7m. With a performance standard of three totally negative detections from consecutive surveys they were able to declare in July 2006 that both lagoons were totally free of exotic caulerpa(8). However, caulerpa popped up again in March 2021 when an incursion of Caulerpa prolifera was detected in Newport Bay, near Los Angeles, which triggered reactivation of the SCCAT and development of a Rapid Response and Eradication Plan(9). For this incursion suction dredging was employed as the primary treatment to remove caulerpa, as the topography and hydrology of the site was not suitable for their preferred method of tarpaulins and chlorine treatment. While regrowth of residual caulerpa fragments has since occurred, growth and spread has been prevented by a combination of manual weeding and strategic placement of hypochlorite pellets on the regenerating caulerpa. Since the initial treatment the native eelgrass has regenerated paving the way for ecological restoration of the site. 

Surveillance and ongoing treatment are continuing in California, but the SSCAT is confident that the outcome here will also be eradication. You can find out more about the Californian approach through a Webinar by marine biologists, Rachel Woodfield and Robert Mooney, that was part of the 2023 California Invasive Species Action Week Lunchtime Talks(10). 

How Biosecurity New Zealand has dealt with it 

In comparing California with what has happened at Aotea I am drawn to the conclusion that the level of surveillance, preparedness and response has been a monumental failure. Even though it is well known that Aotea is a sentinel site in New Zealand for marine invasives because of the prevailing currents and winds, and the patterns of yacht movement, there is very little surveillance of our waters. There is no regular MPI surveillance of any of the bays and harbours and only annual visits from Auckland Council Biosecurity divers, despite Aotea’s marine zone being recognized in the Auckland Unitary Plan as Outstanding Natural Landscape. Caulerpa is now the fourth invasive species to be detected in Aotea waters in recent years with sea squirt, fan worm and Asian Paddle crab being the first three. There is anecdotal evidence that locals in Okupu noticed the green seaweed but did not realise it was a serious invasive pest, highlighting the need for initiatives like Ahu Moana that are community led. Two pilots, led by Glenn Edney from the Tūtūkākā coast, have been underway at Schooner Bay and Katherine Bay and their associated communities over the last year. 

In contrast to the high level of preparedness in California, the level of surveillance and preparedness in New Zealand for a caulerpa incursion has been found wanting. This is despite caulerpa being highlighted as a potential serious marine invasive at several marine biosecurity conferences since the early 2000’s, and in a vast array of reports, conference proceedings(11), publications and management plans following the invasion in the Mediterranean in 1984 and subsequent invasions in Australia and the USA in 2000. It was such a high priority in the USA that a national management plan was developed in 2005(12). 

After detection at Okupu in June 2021, Biosecurity NZ did respond quickly but the lack of a management plan to control or eradicate meant the incursion totally got away on them. While it was always going to be difficult to contemplate eradication at Okupu, the relatively small incursions in Tryphena and Whangaparapara harbours could have been contained and probably eliminated if the response had been as rapid as in California, using the methods they used successfully. 

Since early 2022 there has been no further surveillance on Aotea. Locals have reported sighting caulerpa in the bays to the north of Whangaparapara, on the reefs on the outer Tryphena harbour and even on Goat Island around the SE coast! These reports are alarming given the very serious impacts this exotic seaweed is known to have on marine life. Experience in the Mediterranean has seen a 30% reduction in biodiversity and a 50% reduction in fish biomass in 6 years(13). 

Although there are CANs in place, commercial trawling and dredging, a very high-risk activity for spreading caulerpa, continues along the edges of the CANs. Given it can grow to depths of around 40m in clear waters, a complete ban on commercial trawling and dredging within the 40m contour around Aotea should be put in place immediately. Even with such controls, storms and currents will break up and disperse the caulerpa. This was very evident after 50 tonne-plus of caulerpa washed up on Okupu beach after cyclone Gabrielle in February of this year. This was visually confronting and really brought home to the community the magnitude and the scale of risk we are dealing with. Even the clean-up of this large volume of seaweed on the beach was poorly handled, with bags of caulerpa sitting on the beach for weeks. This event and general concern by communities on Aotea and around the Hauraki Gulf finally led to a public outcry in May over the lack of action and the potential social, environmental and economic impact on the Gulf. 

SO WHAT CAN WE DO?

After two years, it’s clear that a change in the response from government is needed now or we will soon have caulerpa in every bay on the Barrier and in many other places. There is also no doubt that communities will have a role to play in the next stage of this campaign, because they will bear the costs of caulerpa if it is not removed. We felt there had to be greater public awareness of the threats posed by caulerpa to create pressure on and to get faster action from both central and local government. We contacted Andrea Vance from Stuff and worked with her on a story that captured all the issues(14). We presented to the Hauraki Gulf Forum on the 12th of June alongside the Waiheke Marine Project (WMP). This community group have led the way in preparing for spread of caulerpa in the Gulf by initiating their own surveillance of the Waiheke bays using two remotely operated vehicles (ROV)(15). WMP also initiated a conversation with the Californian biosecurity group and had begun sharing this information with their members and the wider community through events such as the Waiheke Pestival. Submissions to the Minister of Biosecurity, Damian O’Connor, were made by Legasea, Revive our Gulf, and by the Chairs of Ngāti Rehua Ngātiwai ki Aotea and Ngāti Paoa Iwi Trusts(16). 

But things really hotted up when Te Rāwhiti environmental restoration and pest control specialist, Rana Rewha (Ngāti Kuta) found clumps of caulerpa on the beach at Omakiwi Cove, in the Bay of Islands(17). This resulted in a major reaction from the Northland Regional Council on the underwhelming response of government. While it is somewhat galling for Aotea that it takes an outbreak on the mainland to galvanise national action it is now great to hear from Biosecurity NZ that “nothing is off the table”, according to John Walsh, who is leading the response. The community of Te Rāwhiti have seen what has happened on Aotea and there is a commitment and determination that not just control but eradication should be the goal for “this maggot of the sea”, to quote Kaumātua Hone Martin from Te Rāwhiti(18). 

Community concerns about the incursion came to the fore at the Hauraki Gulf Forum on the 12th June. Both John Walsh (Director Readiness and Response Services, MPI) and Stuart Anderson (Deputy Director-General, MPI) were there alongside representatives from Auckland Council, Northland and Waikato regional councils, and most of the key environmental groups that are active in the HG. Chair Kate Waterhouse and I presented on behalf of AGBET our concerns about the management of the caulerpa incursion at Aotea(19). 

Among our key messages was a call for: 

• The establishment of a new, cross-agency collaborative response model to enable local surveillance, control and possible eradication. 

• Provision of funding to establish an Aotea specific response project, with locally based management, surveillance equipment and diving capability, training and compliance, and access to the full range of proven control and removal tools. 

• Banning the use of all bottom contact fishing methods along the west coast of Aotea to help control the spread of caulerpa, until there is data on the depth caulerpa can grow to in our waters so exclusion zones can be more robustly defined. 

An outcome of this hui was a letter to Minister O’Connor voicing the serious concerns of the Hauraki Gulf Forum that “the arrival of caulerpa is the most serious marine biosecurity incursion in our lifetime”. We are all waiting to see how the government responds. 

One significant step taken by MPI indicating they are at last taking this incursion more seriously has been the establishment of a Suction Dredge Technical Advisory Group to consider suction dredging as a tool for management of exotic caulerpa. This committee of 12 has a wide range of expertise and experience with the brief of preparing a report by the 30th of July. As co-chair of this committee, with Mata Hone Martin from Te Rāwhiti, I will be pushing strongly for this report to made public. It is disappointing that the initial TAG report released in February 2022(6) is still not readily available in the public demand. I did receive a redacted copy after waiting two months from an OIA request! To establish trust with communities there is a need for much greater transparency and openness from Biosecurity NZ. 

IN CONCLUSION: TIME FOR A STEP CHANGE IN RESPONSE TO HEAD OFF DISASTER

Exotic caulerpa in our waters is the most serious marine incursion of our time. The response so far has highlighted severe deficiencies in marine biosecurity surveillance, preparedness and our collective ability to respond. It is clear that marine biosecurity is the very poor cousin of land-based biosecurity. One cannot imagine such a slow response from government if we had an incursion of ‘foot and mouth’ disease, for example. There is a way forward but it is one that requires much greater inter-regional and inter-organisational cooperation, and urgency. Importantly, there needs to be greater empowerment of local communities by training, certifying and resourcing them to provide the level of surveillance and responsiveness needed to not just help manage this incursion but to prevent any new incursions remaining undetected for so long. We need look no further than to California for the level of preparedness and ability to respond rapidly to serious incursions like caulerpa. Until we have such management and response plans in place we cannot claim to be “a world leader in biosecurity” and our marine environment which is so important to us will decline and degrade. 

Postscript:

Since this article was written exotic caulerpa has been detected in the northern channel off Kawau island and very recent surveillance by NIWA at Aotea has confirmed, what the locals had already suspected, that caulerpa has been detected at Bowling Alley Bay, the Broken Islands (?) and the Southern end (?) of Port Fitzroy. We all know that the most effective measure to control this horrible weed is a rapid response. We await with bated breath to see when/if a rapid response is initiated as this will be a tipping point for control of caulerpa on Aotea. 

Acknowledgements:

We acknowledge the matters set out in the letter sent to ministers by Ngāti Rehua Ngātiwai ki Aotea together with Ngāti Hei in May. Until recently MPI’s processes and governance have failed to properly reflect the concerns of both ahi kā and the community on Aotea. 

We acknowledge the tireless work of Local Board Chair Izzy Fordham on the governance group to date as the only Aotea resident included. 

We acknowledge the people of Okupu and the western bays of Aotea who have been directly affected by this infestation and those whose vigilance lead to its discovery in the first place, and the work of Glen Edney in recording the spread of this marine scourge in Schooner Bay as part of the Aotea Ahu Moana project. 

We echo concerns about the slowness of the response and the poor and slow response from councils.

References:

1. iNaturalist, post by Jack Warden on 24th June 2021 https://www.inaturalist.org/observations/84272350 

2. Aotea Great Barrier Environmental News article by Barry Scott (Issue 45 Summer 2022) https://www.gbiet.org/en45- caulerpa-brachypus-invasion 

3. Susan Botting Stuff ‘Caulerpa invader seaweed found in Bay of Islands, Northland’ (19th May 2023) https:// www.nzherald.co.nz/northern-advocate/news/caulerpa-invader-seaweed-found-in-bay-of-islands-northland/ TEAPHVXLHVEY5KBAPIWDSO3YRU/ 

4. Kate Evans Killer algae’ for New Zealand Geographic (Issue 177 Sep/Oct 2022) https://www.nzgeo.com/stories/killer-algae/ 

5. Biosecurity New Zealand, Technical Advisory Committee report. Caulerpa Great Barrier Island 2021 Response. February 2022, Published by MPI, Wellington. 

6. Steering Committee of the Southern California Caulerpa Action Team. February 2005. Southern Californian Caulerpa taxifolia eradication program. Caulerpa taxifolia survey efficacy assessment at Agua Hedionda lagoon and Huntington Harbour. 

7. Steering Committee of the Southern California Caulerpa Action Team. May 2006. Final report on the Eradication of the invasive seaweed Caulerpa taxifolia from Agua Hedionda lagoon and Huntington Harbour, California. 

8. San Diego Regional Water Quality Control Board (2006). Eradication of destructive, invasive, non-native seaweed announced. 

9. Southern California Caulerpa Action Team (2021). Rapid response and eradication plan for the invasive green alga Caulerpa prolifera in Newport Bay. 

10. Rapid Response and Eradication of Caulerpa in California: Lessons Learned. Webinar by marine biologists Rachel Woodfield and Robert Mooney as part of the 2023 California Invasive Species Action Week Lunchtime Talks (5th June 2023) https://ucanr.edu/sites/invasivelunch/2023/ 

11. International Caulerpa taxifolia conference proceedings. January 31-February 1, 2002. San Diego, California, USA. 

12. Aquatic Nuisance Species Task Force (2005). National management plan for the genus Caulerpa. A report prepared by a Caulerpa Working Group under the auspices of ANSTF. 

13. Harmelin et al. (1999). 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. 

14. Andrea Vance, 21st May 2023. Stuff article ‘An environmental disaster on the scale of the Rena’ https://www.stuff.co.nz/ environment/132068603/killer-seaweed-invasion-is-an-environmental-disaster-on-the-scale-of-the-rena 

15. Craig Thorburn, Waiheke Marine Project, presentation Clearing up Caulerpa at Waiheke Pestival (23rd April 2023). 

16. AGBET Caulerpa Project https://www.gbiet.org/caulerpa 

17. Bay of Islands shudders as Caulerpa identified in more than a dozen locations. RNZ (30th May 2023) https://www.rnz. co.nz/news/national/490962/bay-of-islands-shudders-as-caulerpa-identified-in-more-than-a-dozen-locations 

18. CAN put in place in Omakiwi Bay to control the “maggot of the sea” to quote Kaumatua Hone Martin (12th June) https:// www.rnz.co.nz/news/ldr/491853/bay-of-islands-anchoring-ban-now-in-place-to-fight-caulerpa-spread 

19. AGBET presentation to Hauraki Gulf Forum, 6th June 2023. Summary of Key Points: Caulerpa Response https://www. gbiet.org/caulerpa