(Undaria pinnatifida)
Regional Surveillance Pest

(Undaria pinnatifida)

Regional Surveillance Pest

A large stalk floating in water.

Undaria is an edible Asian seaweed that grows on rocky habitat and marine structures. A mature Undaria plant is distinguished from native kelp by its “frilly” sporophytes (spore-producing structures) near the base of the plant, and a central rib along the fronds. It is an annual, growing rapidly in spring and early summer and then dying back. It was first discovered in Wellington harbour in 1987, and probably arrived on a vessel or in ballast water. It has spread rapidly on vessels and currents, becoming established along many parts of the New Zealand coastline.

Reasons for the Strategy

A dried stalk of plant laying on a wooden deck.

Undaria spread rapidly from Port Nelson onto the Boulder Bank and Haulashore Island, and is present on marine farms in Golden Bay. It has the potential to occupy rocky habitat along the Tasman and Nelson coastlines and modify the ecology and “natural character” of highly valued coastal areas such as Abel Tasman National Park.

Undaria is assessed at “5” on the infestation curve. The best option is for the Councils to continue surveillance on the distribution of Undaria, and to provide advice and education to vessel owners on identifying and controlling Undaria by removing it before spores are being produced. It has been declared an unwanted organism.


To gather information on the presence of Undaria in sites of high public value in the Tasman-Nelson region during the term of the Strategy.

Alternative Measures

The inclusion of Undaria in the Strategy, with a focus on education and surveillance, is appropriate to facilitate the voluntary control of the plant. The principal alternative
measure is to adopt a greater level of regional intervention, such as requiring all vessel owners to control Undaria on their vessels. However, this option would only be effective if adopted nationally and it is too widespread to achieve any significant benefits.

Biosecurity Act Requirement

No person shall knowingly sell, propagate, breed, release, or commercially display Undaria, under Sections 52 and 53 of the Act.