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Undaria seaweed risk to Auckland region’s waters

Undaria seaweed risk to Auckland region’s waters

13 July 2005

The Auckland Regional Council wants people to report sightings of the invasive seaweed Undaria, first identified in the Waitemata Harbour in September 2004 and now potentially threatening Auckland’s coastal waters.

Parks and Heritage Committee Chair Sandra Coney said today the Asian seaweed, farmed as a food crop in Japan, China and Korea, was first discovered in Wellington Harbour in 1987 and had progressively spread around the country.

“Our coastline is the jewel in the crown of Auckland’s environment. This seaweed can rapidly colonise coastal ecosystems and artificial structures and threatens the Hauraki Gulf and pristine Northland harbours.

“It can displace native kelps, restrict the lifecycle of shellfish like paua and poses a significant threat to aquaculture.

“I am also concerned about the possible impacts of Undaria on our regional parks - many of which have beautiful coastline with popular beaches and amenity areas.

“It was originally thought unlikely that Undaria could survive north of Gisborne because our waters are warmer. It appears that is not in fact the case.

“We want Aucklanders to help us determine how far this pest has spread,” Cr Coney says. “At this stage we don’t know enough. It has so far been found only in Westhaven and Viaduct Harbour.

“If people find this pest anywhere else they should call 366 2000.”

Cr Coney says stopping the spread of the seaweed could be expensive.

“There is a very big question regarding whether the ARC alone can take action to prevent any further spread, before the seaweed becomes too hard to manage.”

The ARC, which has a biosecurity role through helping to protect the region from unwanted plant and animal pests, wants to urgently discuss what options there are for central Government to help control the seaweed.

“The Council resolved today to raise this matter with the Minister for Biosecurity and the Minister of Conservation,” Cr Coney says.

“We will be asking those Ministers what options there are for the co-ordinated control of Undaria in the Auckland region and nationally.”

Despite Undaria being declared an unwanted organism under the Biosecurity Act 1993 and listed as one of the world’s 100 worst alien invader species by the International Union for the Conservation of Nature (IUCN), Biosecurity New Zealand does not regard Undaria as a priority and has not been willing to fund control measures. The Department of Conservation is understood to have no funding for a control programme after ending, unfinished, a successful programme that had removed about 20,000 Undaria plants per year from Stewart Island.

ARC Biosecurity Manager Jack Craw says several regional councils with less high value marine habitats than the Auckland region have also decided to take no action, because a Ministry of Fisheries national management strategy in 2000 concluded that the seaweed could not be eradicated.

“The ARC could tackle the seaweed but our expertise in dealing with a marine invader is untested. Any control programme would rely on voluntary cooperation from boaties and residents reporting infestations,” Mr Craw said.

The Parks and Heritage Committee has asked for another report next month on the distribution of the seaweed in the Auckland region and the estimated costs of eradicating or controlling it.


Photos of Undaria are available on the ARC website, courtesy of the Cawthron Institute. Please credit Cawthron Institute. Further information and images are also on the Department of Conservation website www.doc.govt.nz

Identification: Undaria is a golden brown seaweed with a frilly reproductive structure at its base, which native seaweeds do not have. Undaria also has a central midrib running the length of the main frond, which most native seaweeds do not have.

Notes for Editors: The seaweed Undaria pinnatifida was first discovered in Wellington Harbour in 1987 but nothing was done to contain its spread although its potential impacts were recognised. In 1997 an infestation on Stewart Island was discovered. Initial attempts to eradicate the seaweed failed however until a method of heat treatment was successfully developed to remove the seaweed from a heavily fouled sunken fishing vessel in the Chatham Islands.

The Stewart Island programme was effectively managed by the Department of Conservation although full eradication – the department got down to removing about 70 plants a year from about 20,000 - was not achieved before funding ran out.
Until recently it was thought the risk of the seaweed spreading north of East Cape and infesting marine reserves was relatively low because of warmer water temperatures.

The Government decided that parks and islands in southern waters should be targeted as a preferred management option for Undaria. The seaweed was first discovered in the Auckland Viaduct Harbour and Westhaven Marina in late September last year by a Japanese scientist. Later research indicated the seaweed had been around for up to five years. Isolated pockets of the seaweed have spread as far as Jellicoe Wharf but densities have mostly been recorded in western parts of the port. A delay in managing the spread of the seaweed increases the chance of it getting out of control in Auckland, particularly around high value areas.

Undaria can successfully compete against native species in coastal ecosystems and can rapidly colonise bare underwater space. It matures early – its growing season begins in September and it is broadly tolerant of different environmental conditions. It grows quickly reaching one to two metres long and can form dense canopies preventing other seaweeds from growing. Its spread can be helped by human activities. It can foul marine farms, boats and wharves as well as other artificial structures.


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