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.

• Size: Fronds grow up to 10 cm long.
• Appearance: Green fronds shaped like oar blades, rising from long runners or stolons. Grows between 2 and 30 meters below the tideline on both hard surfaces and sandy areas.
• Similar species: Looks similar to native seaweeds but has a distinctive oar blade-shaped frond.
• Habitat: Found on hard surfaces, sandy areas, and in both shallow and deeper waters, often forming dense mats that can extend up to 40 meters deep.

Late spring to early autumn (October to April in the Southern Hemisphere). 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. Surveys during warmer months can effectively identify new or expanding patches when the seaweed is at its most vigorous growth stage.

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

ORC is currently developing a marine biosecurity programme and needs to obtain more information on species distributions before pursuing management options. If you think you have spotted exotic caulerpa, please let us know by calling 0800 474 082 or emailing biosecurity@orc.govt.nz

Preventing the spread of Exotic Caulerpa is the best strategy, as removal of invasive marine pests is both difficult and expensive.

Cleaning your craft and gear for biosecurity purposes is an important way to help protect the marine environment. Just as regular maintenance keeps your equipment in good condition, biosecurity cleaning keeps the ocean healthy for everyone.

The three main types of marine biosecurity cleaning for boaties are: