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.

Exotic caulerpa has 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.
• Similar species: Looks similar to native seaweeds but has a distinctive oar blade-shaped frond.
• Distinctive features: fronds resemble oar blades. Exotic caulerpa creates dense underwater fields where nothing else can grow.
• Habitat: Grows between 2 and 35 metres below the tideline in 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