Caulerpa Brachypus, the Invasion by this Non-native Seaweed
BARRY SCOTT (with Biosecurity New Zealand and NIWA)
In July 2021 Biosecurity New Zealand announced that an invasive non-native seaweed had been detected in Blind Bay. Underwater surveillance by NIWA showed that it was very widespread across the seabed in this bay. An extension of this surveillance to neighbouring bays revealed that pockets of the seaweed were also present in Tryphena and Whangaparapara harbours. Following discussion with Aotea mana whenua, Aotea Great Barrier Local Board, Auckland Council and the Department of Conservation, Biosecurity New Zealand imposed legal controls on Blind Bay, Tryphena Harbour, and Whangaparapara Harbour in the form of a Controlled Area Notice (CAN). Mana whenua supported this response with the establishment of a rāhui over the same areas. Detection of this highly invasive seaweed is of considerable concern, so what do we know about it and what are the future plans for managing it?
Background
Non-native Caulerpa brachypus on edge of Blind Bay Harbour (Photo: Jack Warden)
In June 2021, an image of a seaweed in Blind Bay that appeared to be non-native to New Zealand, was posted on the citizen website iNaturalist(1),(2) by Jack Warden, a resident of Aotea Great Barrier. Sergio Díaz-Martínez, a researcher from the National Autonomous University of Mexico who had previously worked at NIWA, spotted the entry and noted it appeared to be a Caulerpa species not present in New Zealand. He tagged a NIWA scientist who swiftly notified Biosecurity New Zealand and arranged for samples to be collected from Blind Bay. The Marine Invasive Taxonomic Service at NIWA identified the samples as Caulerpa brachypus (Harvey, 1860), a non-native marine macro-alga not previously detected in New Zealand(3). C. brachypus is a seaweed native to the Indo-Pacific region, ranging from Africa to Australia, the Pacific Islands and Japan. It has blade-shaped fronds that are up to 10 cm long, arising from long runners known as stolons. There are two native species of Caulerpa in New Zealand that could be confused with C. brachypus; C. articulata and C. brownie, but their morphology is very different(4). A close relative, C. taxifolia, listed as a Notifiable Organism under the Biosecurity Act, has been bred for use in the aquarium trade, and has become established as a serious aquatic weed In NSW(5).
Biosecurity New Zealand response
Following the initial detection of C. brachypus in Blind Bay, through a Mana – Enhancing Agreement, Biosecurity New Zealand in partnership with Aotea mana whenua, Aotea Great Barrier Local Board, Auckland Council and the Department of Conservation responded to the incursion.
Non-native Caulerpa brachypus on edge of Blind Bay Harbour (Photo: Jack Warden)
The response, which operates under a formal structure outlined under the Coordinated Incident Management System (or CIMS), set out to understand the distribution of the exotic Caulerpa, contain the known sites of infestation, and work collaboratively on potential management and surveillance options. Almost immediately they commissioned NIWA to carry out a dive survey of Blind Bay to determine the extent of the invasion. Video footage showed extensive spread of this seaweed across the floor of the bay(6). Further dives in Tryphena Harbour revealed pockets of C. brachypus in this harbour as well(7). As this species can have impacts on native marine organisms and ecosystems, to minimise its spread, Biosecurity New Zealand placed a Controlled Area Notice (CAN) on Blind Bay and Tryphena Harbour on 20th September 2021. Mana whenua supported this response with the placement of a rāhui over the same areas.
Further surveillance in September showed an exotic Caulerpa species was also present in Whangaparapara Harbour, so the CAN controls and rāhui were extended over this bay as well on 16th October 2021. The CAN and rāhui are in place until 30th June 2022(8).
In essence, the CAN makes it illegal to take any marine life (e.g. fish, shellfish, crayfish, seaweed) from the three affected harbours. Vessels that have anchored in the three areas require a permit from Biosecurity New Zealand to lift anchor and move.
These rules are in place because C. brachypus is easily broken up and spread by activities such as dredging or anchoring.
For full details of the CAN rules, maps of the controlled areas and what to do if you think you spot C. brachypus go to the MPI web site: www.biosecurity.govt.nz/caulerpa (4),(7)
Two Species
After the initial confirmation that the Caulerpa species found in Blind Bay was C. brachypus, further molecular analysis was carried out on samples from Tryphena and Whangaparapara harbours. Surprisingly, two closely related species were found to be present in Tryphena: C. brachypus and Caulerpa parvifolia. Only C. parvifolia has been found in Whangaparapara Harbour. Both species are very similar in morphology and growth habit and can only be distinguished by genetic testing. While this is scientifically interesting, that knowledge does not alter response operations. While the source of this introduction is currently unknown it is thought likely to have been introduced on fishing or boating equipment, such as an anchor or anchor chain.
Native Caulerpa Articulata (Photo: Dr John Huisman)
Pathway Going Forward
Managing marine invasions is even more difficult than managing the invasion of weeds on land. The ability of C. brachypus and C. parvifolia to reproduce asexually from small vegetative fragments, and the growth habit of spreading by stolons along the sea floor, make this incursion particularly challenging.
To help them in this task, the governance group has set up a technical advisory group (TAG) of nine international and national experts, together with mana whenua representatives to provide mātauranga input, to brainstorm how this invasive species might be controlled and managed. The TAG is charged with providing independent, innovative and technical advice on potential tools to manage C. brachypus and C. parvifolia.
Initially they will focus on identifying tools and techniques that are available or need to be developed to manage Caulerpa on a large scale. They will consider whether the tool or method has the potential to suppress, contain, control or eliminate Caulerpa, whether a commercial benefit could be obtained from harvest to off-set control costs, and whether the tool or method could be used on other species in New Zealand. The response team is also interested in knowing whether there are any new and innovative treatments on the horizon that could be considered in the medium to long term, and what sort of re-invasion risk Caulerpa poses.
As a preliminary approach, NIWA, under contract to Biosecurity New Zealand, carried out small scale treatment measures in Whangaparapara and Tryphena Harbours, applying salt to kill the seaweed by osmotic shock. The treated areas were covered with hessian and tarpaulins to contain the salt and shade out any plants that survived the initial treatment. Salt has been used successfully to manage the spread of C. taxifolia in NSW, Australia(9).
The salt will affect some local marine species in the small areas that are treated, but they are likely to recolonise the treated area within months. Where possible, some species such as scallops were removed from the treatment area before the salt was applied. This method may not be a viable treatment for the widespread infestation in Blind Bay, so alternative methods may need to be explored.
Surveillance of Our Coastline for Invasive Species
As disappointing as this invasion is, the identification of the species by an informed member of the community highlights the important role citizen science, through such media as iNaturalist, can play in keeping New Zealand free of other invasive pest species. Given the New Zealand coastline is over 15,000 km in length, it is almost impossible for regulatory bodies to survey every bay, harbour and fiord of the coastline. Instead, they regularly survey potential ‘hotspots’ such as points of arrival by commercial ships and yachts.
Biosecurity New Zealand contracts NIWA to carry out the marine high risk site surveillance programme where regular winter and summer checks are made of all the major ports and Opua Marina, Bay of Islands (where most overseas yachts arrive).
However, many New Zealanders dive at various locations around the country, so it is important they are aware of the species present and inform MPI if they come across what they believe is an unknown species. Suspected sightings can be reported to Biosecurity New Zealand’s pest and disease hotline: 0800 80 99 66.
Good information can be found at: https://www.marinebiosecurity.org.nz/what-are-marine-pests/
Postscript
The recent Biosecurity New Zealand updates (23 December 2021 and 28 January 2022) had a mixture of good and bad news. NIWA divers found that the patches of Caulerpa in Whangaparapara and Tryphena harbours had grown from 10 to 1750 square metres in the former and from 0.01 to 1840 square metres in the latter since their September dives (Update 5). Where a thick layer of coarse salt was applied in plots in Whangaparapara and Tryphena Harbours no Caulerpa was seen indicating the treatment method is effective (Update 7). The challenge now is whether this treatment can be scaled up.
Acknowledgments
I would like to thank Lesley Patston (Principal Adviser, Biosecurity Communications, Ministry for Primary Industries/Manatū Ahu Matua), David Yard (Principal Advisor Response, Biosecurity New Zealand/Tiakitanga Pūtaiao Aotearoa) and Barb Hayden (Science Advisor Marine, NIWA/Taihoro Nukurangi) for generously sharing information, answering my questions and checking final copy of this article.
References:
iNaturalist link: https://www.inaturalist.org/observations/84272350
Marine Pests post: https://www.marinepests.nz/news/local-fisherman-first-to-detect-invasive-seaweed-at-aotea-great-barrier-island
Biosecurity Response Sheet: https://www.mpi.govt.nz/dmsdocument/46393-Caulerpa-Great-Barrier-Island-2021-Biosecurity-Response-Fact-sheet
Link to controlled area notice: https://www.mpi.govt.nz/dmsdocument/47623-Information-sheet-on-Caulerpa-brachypus-and-the-Controlled-Area-Notice
Glasby et al. (2005). Experimental use of salt to control the invasive marine alga Caulerpa taxifolia in New South Wales, Australia. Biological Conservation 122: 573-580. https://www.sciencedirect.com/science/article/abs/pii/S0006320704004124
Link to video footage of Caulerpa brachypus on seabed of Blind Bay: https://www.facebook.com/watch/?v=1455558218133461
Caulerpa brachypus update: https://www.mpi.govt.nz/biosecurity/major-pest-and-disease-threats/caulerpa-brachypus-a-non-native-seaweed/
Creese et al. (2004). Eradicating and preventing the spread of the invasive alga Caulerpa taxifolia in NSW NSW Fisheries Final Report Series No. 64. ISSN1440-3544.