24 April 2024
Kia ora koutou
In this update we look at progress in the Exotic Caulerpa Accelerated Programme and advise on two new locations of exotic caulerpa in the Hauraki Gulf.
Good progress in surveillance and removal projects
Collaborative work between Biosecurity New Zealand, regional councils, and mana whenua is well underway, testing technology to find and contain caulerpa and then remove it, where possible, from some affected areas.
Just yesterday, NIWA divers, working closely with Ngāti Manuhiri partners, entered the water at Iris Shoal near Kawau Island to survey the caulerpa patches there.
NIWA divers prepare to enter the water at Iris Shoal - Photo: Ihipera O'Kane, Te Au ō Moana
Following tikanga and in perfect weather conditions, the divers were underway, collecting information to inform suction dredging, which is expected to start on Friday (26 April). While the caulerpa at Iris Shoal is in a small and sparsely spread area, it is in a difficult marine environment with changing depths, tides and currents. The work is expected to continue until approximately 11 May (weather permitting).
In Northland, where large-scale suction dredge technology is being trialled, the current focus is installing equipment to separate sand from material sucked from the seabed.
The barge that carries the mechanical suction dredge is currently in Opua for the attachment of two trommels (sand separators) which will allow sand to be separated from the dredged exotic caulerpa so the process is faster and more efficient. We are optimistic that the equipment will be ready for operational use shortly.
Two large trommels are mounted on the suction-dredging barge at Opua - Photo: Northland Regional Council
As a part of this project, Northland Regional Council (NRC) has begun an intertidal trial in collaboration with local hapū, Patukeha and Ngāti Kuta. This work is to test and find the best treatment (salt, bleach, chlorine granules, dishwashing liquid, or matting e.g. harakeke) to remove exotic caulerpa in an intertidal zone. This is an add-on to the suction dredge trial as the large suction head cannot be used over shallow, rocky areas.
At Aotea Great Barrier Island, a project led by Auckland Council is testing how to manage the perimeters of identified priority areas of exotic caulerpa. What we learn from this trial will inform how we can best slow the spread of ‘creeping’ expansion in areas of infestation. The work is planned to begin in early May, focused on the Man o’ War Passage (Port Fitzroy), Motuhaku Island (Port Abercrombie) and Katherine Bay.
To enhance public awareness, staff are working with Department of Conservation to get signs installed at a number of smaller Auckland islands - Rangitoto, Motutapu, Motuihe, Tiritiri Matangi, Motuora and Kawau. Posters are now in place at 28 boating clubs in priority regions. Online, an exotic caulerpa digital campaign runs through to June, with targeted interest-based ads on Facebook, Met Service, and other broad-reaching platforms.
New detections of exotic caulerpa in Hauraki Gulf
These new detections are disappointing but not unexpected, given the ability for exotic caulerpa to be moved over long distances on vessels and marine equipment.
We’re working with partners and those people most closely associated with the new affected areas to determine the most appropriate response to this discovery.
The immediate focus is undertaking some rapid, targeted surveillance to better understand what we are dealing with and whether removal of the exotic caulerpa is feasible.
The new population at Mokohinau Island was brought to our attention by scientists working in the area who submitted photos of suspected caulerpa.
The Rakino Island incursion was found by Auckland Council staff carrying out surveillance for exotic caulerpa and who sent us photos.
NIWA’s Marine Invasives Taxonomic Service scientists have confirmed exotic caulerpa from the images. Analysis of samples will be required to formally identify the actual species at the new locations.
The Mokohinau Islands are administered by the Department of Conservation and are uninhabited but a destination for boating, fishing and diving.
The exotic caulerpa was found at a depth of approximately 23 metres in the Edith Passage just east of Motupapa and Hokoromea Islands.
Rakino Island, near Motutapu and Waiheke Islands, has a small number of residents, and is also a marine recreational area. Approximately one square metre of exotic caulerpa was found in Woody Bay at a depth of about seven metres.
Exotic caulerpa is currently found at five other upper North Island locations - Aotea Great Barrier Island, Ahuahu Great Mercury Island, Waiheke Island, Kawau Island and Te Rāwhiti Inlet in Northland.
Technical advice reports available online
Actions and decisions made for the exotic caulerpa response are being informed by scientific advice. Recently, new technical reports have been posted to our caulerpa web page.
These include technical advice on a long-term management strategy for exotic caulerpa (February 2024); Aotea exotic caulerpa removal trial (National Institute of Water and Atmospheric Research (NIWA)), February 2024); and impact of exotic caulerpa on native species – Phase 2 report (NIWA, December 2023).
Nāku noa, nā
The Caulerpa response team
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For more information about exotic caulerpa seaweeds in New Zealand visit the Ministry for Primary Industries Biosecurity New Zealand website.