Exotic caulerpa are highly invasive seaweed species that form dense underwater fields, smothering the seafloor and outcompeting native species for space. They can disrupt local ecosystems, crowding out important marine life like sponges, mussels, scallops, and even native Caulerpa species.

These seaweed species pose significant risks to recreational, cultural, and commercial marine activities. Once established, they are challenging to remove and can spread easily through fragmentation.

Exotic caulerpa have spread rapidly from only a few known sites to areas such as Great Barrier Island and other parts of the northern North Island. There are no known locations of Caulerpa in the South Island, and due to its temperature limits, it is very unlikely to establish here.

• Size: Fronds (leaves) grow up to 10 cm long.
• Appearance: Green fronds shaped like oar blades, rising from long, horizontal runners (called stolons) that can reach up to nine metres long.
• Distinctive features: Fronds resemble oar blades. Exotic caulerpa creates dense underwater fields where nothing else can grow.
• Similar species: Looks similar to native seaweeds but has a distinctive oar blade-shaped frond.
• Habitat: Grows between 2 and 35 metres below the tideline on both hard surfaces and sandy areas. Found in both shallow and deeper waters, often forming dense mats that can extend up to 40 metres deep.

Late spring to early autumn (October to April). These Caulerpa species thrive in warm water conditions, which promote rapid growth and expansion of their mats. During these months, their bright green fronds are more developed and visible, making detection easier.

It is an offence to breed, knowingly communicate, exhibit, multiply, propagate, release, or sell, an unwanted organism (Biosecurity Act 1993).

www.orc.govt.nz/exoticcaulerpa