Undaria
Undaria pinnatifida
Undaria
Japanese or Asian kelp
This species is in New Zealand
General Information
The kelp Undaria pinnatifida (Undaria) is native to Japan where it is cultivated for human consumption. It is a highly invasive opportunistic seaweed which spreads mainly by fouling on boat hulls. It can form dense stands underwater, potentially resulting in competition for light and space which may lead to the exclusion or displacement of native plant and animal species.
Undaria is present in almost all of New Zealand's international ports and harbours ranging from Auckland down to Bluff including Stewart Island and, recently, the Snares, Fiordland and Chatham Islands. It is also found along the top of the South Island. With the exception of a recent small find in Fiordland (April 2010), it is currently not known to have established on the West Coast of the South Island, or large areas of the North Island's West Coast.
Undaria in Fiordland
In April 2010 a single mature undaria plant was found on a line mooring a barge to the shoreline in the remote Sunday Cove in Breaksea Sound. Subsequent investigation found moderately low numbers of plants on the mooring line and the seafloor in the area. It is thought, however, that undaria is not well established in the area.
MAF Biosecurity New Zealand, Environment Southland (Southland Regional Council), and the Department of Conservation have joined forces to try and eliminate undaria from Sunday Cove.
As no further mature plants have been discovered since the original find, regular diving inspections are being carried out so that any new plants found can be removed before they have a chance to reproduce.
Further work is also being done to educate boat owners about good maintenance and hull cleaning to prevent further marine pests reaching Fiordland.
- Fact sheet on Fiordland undaria treatment
(1018 KB) - Biosecurity Magazine – Pest species undaria in Fiordland - P. 26 (1433 KB)
Description
- Undaria Marine Pest Guide (138 KB)
The appearance of Undaria pinnatifida differs depending on its maturity.
Mature plants (as shown above) are a brown/green/yellow colour and grow up to one to two metres. They have a very visible midrib up the plant. They have a holdfast (which anchors them), a stipe (or stem) and a sporophyll (a spiral shaped reproductive structure which produces spores) found at the base of the stipe.
Juvenile Undaria plants (illustrated below) have a holdfast and stem and an undivided blade (they appear as a single leaf). The distinctive midrib starts becoming apparent once the plant grows over five centimetres.
Key identification features
Undaria can look similar to the New Zealand kelp Ecklonia radiata BUT Undaria has a distinctive midrib up the middle of the blade plus the distinctive sporophyll.
Undaria sporophyll
Where Undaria pinnatifida is found
Undaria grows from the low intertidal area to subtidal depths of around 15 metres. It grows on any hard surface including shells, reefs, ropes, wharf piles, vessel hulls, moorings and other artificial structures.
It can form dense "forests" in sheltered reef areas.
Impact
The impacts of Undaria pinnatifida are not well understood and are likely to vary considerably depending on the location. It can change the structure of ecosystems, especially in areas where native seaweeds are absent (Ministry of Fisheries, 2001), and potentially impact on biodiversity.
The weed also has the potential to become a nuisance for marine farms by increasing labour and harvesting costs due to fouling problems.
Spread
While natural spread of Undaria is generally very slow it is easily spread on the hulls of vessels, aquaculture and other marine equipment.
Its spread can be prevented by:
- ensuring vessel hulls and marine equipment are free of fouling, and moored boat hulls are thoroughly coated with antifouling paint
- regularly cleaning hulls in a facility with collection and land-based disposal of fouling material
- minimising the movement of excessively fouled structures from one location to another
Commercial Use
The Government has revised the regime for the commercial use of undaria (May 2010). Outline of the revised regime and supporting documentation.
Media Releases
- Areas designated for Undaria farming
- 19 January 2012 - Working together in Fiordland to oust Undaria - 8 July 2011
- Plastic wrapping Bluff Port protects Fiordland
- Environment Southland media release on detection of Undaria in Fiordland - 23 April 2010
- Government allows increased commercial use of seaweed - Release from Biosecurity Minister David Carter - 7 May 2010
Page last updated: 1 February 2012