Caulerpa - Killer Seaweed Invasion on Aotea Great Barrier Island

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

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

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:

• Waiheke Marine Project - Clearing up Caulerpa (Craig Thorburn’s presentation at Waiheke Pestival).

• Presentation to the Hauraki Gulf Forum - Aotea Great Barrier Environmental Trust’s chair, Kate Waterhouse, and one of our Trustees, Barry Scott, recently presented a series of key points to the Hauraki Gulf Form (12 June 2023). The Trust noted that until recently MPI’s processes and governance have failed to properly reflect the concerns of both ahi kā and the community on Aotea - resulting in concern, anger and now grief from the community over the further spread around the coast. A summary of the key points raised at this event can be read here: Summary of Key Points: Caulerpa Response.

• Video of caulerpa spread at Schooner Bay, Aotea Great Barrier Island.

• Biosecurity New Zealand - Controlled Area Notice (CAN) and the Technical Advisory Report on Caulerpa.

• RNZ Article - Bay of Islands anchoring ban now in place to fight caulerpa spread.

• Californian Reports -

  • A petition to the US Secretary of the Interior

  • San Diego Regional Water Quality Control Board: Eradication of Destructive, Invasive, Non-native Seaweed Announced

  • The Caulerpa Working Group: National Management Plan for the Genus Caulerpa

  • Southern California Caulerpa Action Team: Rapid Response and Eradication Plan for the Invasive Green Caulerpa Prolifera in Newport Bay.

• Scott Simpson - Questions to Minister O’Connor

• NIWA Documents:

  • Situation Report: Aotea and Ahuahu Island exotic Caulerpa Delimitation - 17-18 July

  • Situation Report: Aotea and Ahuahu Island exotic Caulerpa Delimitation - 19 July

  • Situation Report: Aotea and Ahuahu Island exotic Caulerpa Delimitation - 20 July

  • Situation Report: Aotea and Ahuahu Island exotic Caulerpa Delimitation - 21 July

  • Situation Report: Aotea and Ahuahu Island exotic Caulerpa Delimitation - 22 July

  • Situation Report: Aotea and Ahuahu Island exotic Caulerpa Delimitation - 23 July

  • Situation Report: Aotea and Ahuahu Island exotic Caulerpa Delimitation - 24 July

  • Situation Report: Aotea and Ahuahu Island exotic Caulerpa Delimitation - 25 July

• Biosecurity New Zealand have set up an interactive map showing all areas of New Zealand that are suffering from invasive species - Ever wondered if any marine pest species are present in your local bay or harbour? Or keen to check if a marine pest is already known to be in a spot before you report it? A new interactive marine pest map is available on the marine biosecurity portal that can help users to determine what non-indigenous species have been detected at a specific location. 

• AGBET’s “Stopping the Spread: Aotea Caulerpa Response Phase 2: Discussion and Recommendations for the 2021-2023 Governance Group”

• Cawthorn - Report on Prioritising Surveillance Sites for Exotic Caulerpa in Northland

• Aotea’s Suction Dredge Trial - information from the media:

  • Jamie Morton (NZ Herald) - Caulerpa seaweed: Super-spreading scourge to be sucked from seabed in new trial

  • Science Media Centre - Officials to trial removing invasive seaweed Caulerpa – Expert Reaction

• AGBET’s (Kate Waterhouse) article on the “need to know” facts on Caulerpa.

• RNZ Article - Caulerpa invasive seaweed threat spreading - what you need to know

• NZ Herald Article - Aotea/Great Barrier Island: Fears invasive seaweed could cause environmental disaster