Undaria (Wakame) Action Plan

Colour photograph of Wakame (Undaria pinnatifida) plant.


Undaria pinnatifida is a brown macroalgae, originally endemic to Japan. Introduction to Tasmanian waters is suspected to have occurred via ballast water discharged from ships transporting woodchips from the mill at Triabunna. A specimen was first found and identified in 1988 by a local marine botanist sifting through algae washed up on a beach at Rheban on Tasmania's east coast.

A subsequent survey estimated at least 400 tonnes of the algae was present, but the area of infestation was limited to the Triabunna-Rheban region (10 km of coast). A 1994 distribution survey indicated the infestation had spread to over 80 km of coast, from Coles Bay in the north and south to the Narrows (Marion Bay).


This brown algae can grow to 2 metres at maturity. It has an obvious central stem to 10 cm wide that extends for the length of the plant. The blade may be up to 1 metre wide and extends from the tip of the plant for half to three-quarters the length of the plant. Undaria looks similar to the native algae Ecklonia which is in the same family. However, Undaria is clearly identified by the sporophyll (the reproductive segment) which has the appearance of a convoluted or 'frilly' mass of tissue attached to the lower quarter to half of the stem. The Ecklonia stem is bare (see the identification guide).

Action Plan

It was obvious after the initial 1994 survey that an eradication program was not feasible. As a control measure the Department made provision for three licences to wild harvest, process and sell Undaria back to Japan. Because this product originated in Tasmania's unpolluted waters, it has potential to command a high price as a Japanese delicacy with many healing powers.

Further Spread

In January 1997, a diligent photographer observed a small stand of Undaria growing in the Tinderbox Marine Reserve and raised the alarm. The algae was removed, however the specimens indicated that at least one 'seeding' period had already occurred. Outbreaks have now been documented at Tinderbox Marine Reserve, Fortescue Bay, Canoe Bay, Norfolk Bay, Marion Bay and Great Oyster Bay/Schouten Passage.

By reviewing the movement of outbreaks it is now evident that human intervention is spreading the algae.

Environmental Impact

This algae is a very prolific and hardy species. Its growth rate has been measured at 1 cm per day! It can establish a colony on reef or seagrass beds. Because of its amazing growth rate, this weed effectively starves the natural understorey plants of light. As these plants die, the fish move away to find feed elsewhere. This creates extra feeding pressure on adjacent areas. Ecosystems in areas of mass infestation have completely changed.

The weed is capable of quickly sinking buoyed lines with its weight. Aquaculture farm nets require constant cleaning, increasing labour and product costs.

In mooring areas and marinas, boat hulls quickly become infested increasing the likelihood of the weed spreading throughout the State.

What Can You Do?

Undaria is easily spread by boat owners not cleaning and washing boats, trailers, fishing equipment etc after leaving an infested area. A piece of the algae left on a net or anchor will survive for 1-2 days, sometimes more. Microscopic spores floating in water in the bottom of your boat will stay alive for a similar period of time.

On the SlipClean and antifoul boat hulls regularly using environmentally acceptable biocides.
At the Boat RampRemove all pieces of weed, shells and fish from your boat and gear.
Drain bilges, hulls, buckets, gear etc
and let them dry.
At HomeHose all gear, boat and trailer well away from stormwater drains and water courses.
Dry all ropes, wetsuits and other gear.