Caulerpa - Killer Seaweed Invasion on Aotea Great Barrier Island

Caulerpa under a kelp forest on Aotea Great Barrier Island (Photo: Glenn Edney)

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, and soon afterwards the incursion was found to have spread to Ahuahu, Great Mercury Island. 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.

Despite ongoing reporting on the growing issue, including in our summer 2022/23 Environmental News and our winter 2023 Environmental News, little has been done to adequately stop the spread. In addition, the press has recently reported on Caulerpa’s expansion into the Bay of Islands; however, due to the concentration of Caulerpa in this area, particularly in Omakiwi cove and its associated channel, it suggests that it is likely to be the primary site for the incursion - how the community and Northland Regional Council didn’t notice it earlier is a mystery.





Current Enforcement and Next Steps

Aotea Great Barrier Environmental Trust have been pushing for a serious government response to this issue. We want to see:

  1. Containment and eradication to be attempted immediately to contain the spread.

  2. Immediate increase in surveillance to prevent further spread.

  3. A fit for purpose whole of Government response that is proportionate to the scale of the impact of this incursion.

CONTROLLED AREA NOTICES (CAN)

To minimise the spread of exotic Caulerpa species, Biosecurity New Zealand has placed a Controlled Area Notice (CAN) on 3 affected harbours at Great Barrier Island – Blind Bay, Tryphena Harbour, and Whangaparapara Harbour, and over an area of the south western coastline of Ahuahu Great Mercury Island. Mana whenua for the islands have imposed a rāhui on the same areas. These controls are in place until 30 November 2023.

The CAN means that you cannot anchor a vessel in the three harbours under controls – Blind Bay, Whangaparapara Harbour and Tryphena Harbour:

  • Anchoring is only allowed in an emergency (for example to seek shelter in a storm) or with a permit from Biosecurity New Zealand for some limited circumstances (for example if you live at Aotea and need a vessel for routine transport, or for scientific research). A permit is not required in an emergency. To apply for an exemption permit you need to email the application form to: caulerpa@mpi.govt.nz

  • Rod and line and hand line fishing is allowed from the shore, or from structures fixed to the shore – for example wharves and jetties.

  • All other fishing remains prohibited. Spear fishing, gathering kina and crayfish, longlining, net fishing and drift fishing are not allowed.

For more information from MPI, you can view their page here: Exotic Caulerpa seaweeds at Great Barrier, Great Mercury islands, and Bay of Islands (Te Rawhiti inlet).

funding for aotea caulerpa response

Caulerpa at Blind Bay (Photo: Jack Warden)

We are calling for immediate release of funding from MPI and Local Government 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. The locally based management needs to inform a new, cross-agency collaborative response model to enable local surveillance, control and possible eradication.

ban the use of all bottom contact fishing methods

Aotea Great Barrier Environmental Trust seeks to ban the use of all bottom contact fishing methods (dredge, trawl and bottom long lining) along the west coast of Aotea and near other suspected sites, until there is data on the depth caulerpa can grow to in our waters and exclusion zones can be defined. This is a precautionary measure, but one we believe is necessary.


Resources and more information

Beachcast caulerpa at Okupu (Photo: Sid Wales)

For more information on the issue, and how concern has heightened over the past few months, please take your time to read through the following resources:

Caulerpa spread across the sea floor (Photo: Glenn Edney)