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Invasive Seaweed from Asia: WAKAME

Wakame (U. pinnatifida), has been regarded as a noxious invasive seaweed in countries other than its native distribution area. Its introduction to other waters was believed to be through the ballast water of cargo ships from Asia because the spores (gametophytes) contained in the water can survive the long-distance trip.

In New Zealand, Undaria pinnatifida was declared as an unwanted organism in 2000 under the Biosecurity Act 1993. It was first discovered in Wellington Harbour in 1987 and probably arrived as hull fouling on shipping or fishing vessels from Asia.

Wakame is now found around much of New Zealand, from Stewart Island to as far north as Karikari Peninsula. Even though it is an invasive seaweed, in 2012 the government allowed for the farming of wakame in Wellington, Marlborough and Banks Peninsula.

It spreads in two ways: naturally, through the millions of microscopic spores released by each fertile organism, and through human activities, most commonly via hull fouling and with marine farming equipment. It is a highly successful and fertile species, which makes it a serious invader.
However, its impacts are not well understood and vary depending on the location.

This invasive seaweed can change the structure of ecosystems, especially in areas where native seaweeds are absent. By forming a dense canopy which shades the sub-canopy, it can impact the growth of the slow-growing native seaweed species by limiting the underwater solar irradiance and space, thus outcompeting and excluding these native species. For instance, in New Zealand the native coralline algae which are important for paua (edible marine snail) settlement were partially displaced by wakame, resulting in decreased paua recruitment.

Moreover, this invasive seaweed can affect not only the biodiversity of flora, but also the fauna communities which are based on these phytogroups. wakame can grow on reefs which offer refuges for fish, and gradually lead to habitat loss of fishes that dwell on the reefs. Study carried out in the Nuevo Gulf showed that its removal from invaded sites resulted in an increase in the biodiversity at those locations.

NIMPIS, 2002 states that U. pinnatifida has the potential to become a problem for marine farms by increasing labour and harvesting costs owing to fouling problems on fish cages, oyster racks, scallop bags and mussel ropes, which restricts water circulation through cages. The Department of Conservation of New Zealand in its brochure "Gorse of the Sea" state that Undaria could foul mussel farms, salmon farms and boats. Heavy infestations of Undaria may also clog marine farming machinery and heavy fouling of boats is thought to seriously decrease their efficiency.

Information extracted from:  http://www.fao.org/fishery/culturedspecies/Undaria_pinnatifida

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