There are two almost identical species of exotic Caulerpa now known to be in New Zealand waters – Caulerpa brachypus and Caulerpa parvifolia. Together they are referred to as exotic Caulerpa and were first found in New Zealand in July 2021 at Aotea Great Barrier Island.

Photo credit: NIWA

Exotic Caulerpa is a highly invasive seaweed that forms dense underwater fields, smothering the seafloor and outcompeting native species for space. It can disrupt local ecosystems, crowding out important marine life like sponges, mussels, scallops, and even native Caulerpa species. This seaweed poses significant risks to recreational, cultural, and commercial marine activities. Once established, it is challenging to remove and can spread easily through fragmentation.

This invasive species has now been found in Ahuahu Great Mercury Island, Te Rāwhiti Inlet in Northland, Kawau Island, Waiheke Island, Mokohinau Islands, Rakino Island, Fantail Bay, Coromandel Peninsula, and Omaha Cove/Leigh Harbour (although this was a small, discrete patch which has been removed). An interactive map of the known locations can be found here.

Photo credit: NIWA

Fortunately, there are no known locations of Caulerpa in the South Island but if you are travelling north then please keep your boat and gear clean by following these steps:

• When at sea, before moving to a new location, check you anchor and anchor chain, as well as any other gear (e.g. fishing line, cray pots, dive equipment).
• If you find seaweed attached, remove it and bag or contain it securely so it can’t get back into the water. Take it ashore for disposal in a rubbish bin.
• If you can’t contain it securely while at sea, put it back into the waters it came from.
• If you find you’ve picked up seaweed when you’re back at shore, remove it and put it in the rubbish.

If you think you have spotted exotic Caulpera then take a photo, if possible, and note the location. Then either:

• freephone 0800 809 966
• or complete the online form at report.mpi.govt.nz 

Further information can be found here.