Exotic Caulerpa

What does it look like?

Exotic caulerpa is a bright green seaweed with long horizontal runners that can extend up to nine metres, producing many upright fronds. The fronds are flattened with a smooth, distinct mid rib, reaching up to one centimetre wide and typically 15 centimetres long (up to 60 centimetres in deeper water). The small leaf like pinnules attach directly opposite each other along the mid rib.

Two species, Caulerpa brachypus and Caulerpa parvifolia, look identical and can only be distinguished through genetic testing. Both are referred to as exotic caulerpa.

Exotic caulerpa is found below the tideline, from around 2 to 30 metres deep. It grows on hard substrates as well as sandy and muddy seabeds in areas with moderate to high salinity and may also be found washed up on beaches after storms.

Why is it a problem?

Exotic caulerpa reproduces primarily by mainly rapid growth from the runners. It can spread as fragments in the water with storms and currents. It can also be spread by human activities like boating, diving and fishing.

Exotic caulerpa poses a serious threat New Zealand’s marine ecosystems as it spreads rapidly forming vast, dense fields. The plant covers more than 1,500 hectares (August 2024) of the upper North Island seabed. Density ranges from thick carpets in some areas to sparsely distributed plants in others. It can compete with other species for space and upset the balance of local ecosystems.

Caulerpa is easily spread by small pieces on vessels and marine equipment. The seaweed can quickly spread and smother other algae, seagrasses and invertebrate communities, thereby out-competing native species for food and light. This species also produces toxic compounds that are detrimental to other marine species.

Control methods

Physical removal methods at a site must only be done with a consent issued by Ministry of Primary Industries (MPI). You must notify us or MPI if you suspect the presence of this organism. Phone 0800 80 99 66 or online at report.mpi.govt.nz
Take a photo of the pest and note the location and any landmarks.

You can also help prevent the spread of marine pests by:

• Regularly cleaning your boat’s hull – keep fouling growth to no more than a light slime layer.
• Applying a thorough coating of antifouling paint and keep it in good condition.
• Ensure your hull is clean and free of fouling before you travel to a new area.
• Clean and dry any marine equipment (e.g. ropes, lines and pots) before using in a new area.
• Inspect areas on your boat that retain water for signs of marine life.
• Check for aquatic weeds tangled around anchors, trailers and other equipment.

More information

New Zealand has some native species of Caulerpa but the two species identified in 2021 showed similar characteristics to the highly invasive Caulerpa taxifolia, which has been problematic overseas. Caulerpa taxifolia has been listed as a Notifiable Species under New Zealand’s Biosecurity Act since 2001. 

Related links

• Marine pests NZ
• Interactive Caulerpa map
• NZ Marine Pest ID guide pdf
• MPI: Exotic caulerpa in New Zealand - where it is and the work underway
• MPI: Exotic caulerpa seaweeds in New Zealand
• Marine biosecurity: what are marine pests