Caulerpa brachypus: a non-native seaweed

The non-native seaweed Caulerpa brachypus has been found in Blind Bay, Tryphena Harbour and Whangaparapara Harbour on Great Barrier Island (Aotea). This seaweed can spread rapidly and could affect native species. Find out about this unwanted organism and what's being done.

Caulerpa brachypus is a seaweed native to the Indo-Pacific region, ranging from Africa to Australia, the Pacific Islands, and southern Japan. It is considered an invasive pest in Florida, United States, and Martinique in the Caribbean.

Caulerpa brachypus has fronds up to 10 cm long that rise from long runners or roots known as stolons.  In Australia, it grows below the tideline at between 6 and 10 metres on both hard surfaces and in sandy areas. In favourable conditions, it can spread rapidly, forming vast, dense beds or meadows.

How Caulerpa brachypus can spread

Caulerpa brachypus can be spread through breaking into little pieces. This can happen, for example, by wave action or when anchors and fishing gear are moved into or through weed beds.

Fragments are also carried easily on coastal currents. Pieces can get tangled in or stuck on equipment (for example, nets, dive and fishing gear, and cray pots). It can survive out of water for up to a week or more if it's in a moist location (like in an anchor locker or a bunched-up fishing net).

How did this pest get to New Zealand?

It is not known how long this pest has been here or how it arrived. It may have been carried by a visiting international vessel or on a domestic vessel from another, as yet unidentified, infested area in New Zealand.

We do not know how long it has been in Aotea or the scale of the affected area.

What we're doing

Biosecurity New Zealand is working closely with Ngāti Rehua Ngāti Wai ki Aotea and the local community, along with Auckland Council and the Department of Conservation to collectively decide the most appropriate course of action.

A thorough dive survey of Blind Bay was carried out in August 2021. The seaweed was found to be widespread in the bay. It was also found in Tryphena Harbour.

Controlled Area Notice and Rāhui

To minimise the spread of Caulerpa brachypus, Biosecurity New Zealand placed a Controlled Area Notice (CAN) on Blind Bay and Tryphena Harbour, effective from Monday, 20 September 2021. Ngāti Rehua Ngāti Wai ki Aotea imposed a rāhui on the areas which took effect at the same time.

NIWA carried out surveillance checks for Caulerpa brachypus in other areas of the island and found it in a third location – Whangaparapara Harbour. As a result of this detection, the CAN was extended to cover this harbour from 12.01am on Saturday, 16 October 2021. 

The CAN and rāhui are in place until 30 June 2022.

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