Undaria

Undaria is a large invasive seaweed that can grow between 1-2 metres long. It can form dense forests in sheltered areas and compete with native species for light and space.

Description

• Large invasive seaweed, growing between 1-2 metres long.
• Mature plants are brown, green and yellow in colour with a crinkly appearance.
• A distinctive midrib (stem) up the middle of the plant
• They have a holdfast (anchor) which attaches them to surfaces, and a sporophyll (a spiral shaped reproductive structure which produces spores) found at the base.
• Undaria looks similar to the New Zealand kelp Ecklonia radiata, however undaria has a prominent midrib up the middle plus a distinctive sporophyll at the base.

Undaria can tolerate a broad range of temperatures and light levels and grow on a variety of hard surfaces including reefs, ropes, wharfs, vessel hulls and moorings. Undaria is prolific throughout Canterbury coastlines.

It spreads by producing millions of spores and is also frequently transported as biofouling on vessels.

What you need to know

It can spread rapidly and form dense underwater forests; potentially resulting in competition for light and space which may lead to the exclusion or displacement of native plant and animal species.

It has the potential to become a nuisance for marine farms by increasing labour and harvesting costs due to fouling problems.

Management approach

Unwanted organism: An unwanted organism is an organism classified as a pest by the Ministry for Primary Industries (MPI) because it is capable of causing harm to the natural environment, physical resources or human health in Aotearoa/New Zealand.

Rules

Any species declared a pest cannot be sold or be in a place where plants are being sold. Pests cannot be propagated, bred, multiplied, communicated, released, cause to be released, or otherwise spread.

See the MPI website for more information about unwanted organisms.

Control

Protect Canterbury's beautiful waterways and marine ecosystems by keeping a clean hull.

Limiting the fouling on your hull stops pests from catching a ride with you into uncontaminated areas or transferring from your vessel to others when moored or berthed in a marina. Keeping your vessel in good shape will also improve its fuel economy and speed.

Check out our handy guide to good boat maintenance practices..

For more information on undaria and other invasive marine species visit the Marine Biosecurity Porthole website.