Japanese Kelp – Undaria pinnatifida 

Characteristics:
Also known as Wakame, this species is ranked within Europe’s top 100 worst invasive species (NNSS, 2020). Highly adaptable, it can survive anywhere between high tide and 15m deep (Wade, Ames and McKee, n.d.), and in a range of environmental conditions (Oakley, 2007). Consequently, the species has spread throughout much of the globe. 
Undaria pinnatifida reproduces very rapidly via spores that float through the water, and with a growth rate of 1cm per day (NBN Atlas, 2024) the species can spread by 100s of meters annually (Wade, Ames and McKee, n.d.). It grows to about 2m long, appearing as large wavy leaves with raggedy edges (fig. 1), secured to a solid substrate (Oakley, 2007). 

Native Range and Distribution:
Wakame is a popular foodstuff in many East Asian cuisines, and is farmed in its native countries of Japan, China and Korea (Yamanaka and Akiyama, 1993). Its first appearance in Europe was in France in 1971, believed to have been carried on a shipment of Pacific Oysters. Subsequently, the species began to be deliberately farmed in the country (Wade, Ames and McKee, n.d.)
The species quickly hopped the English Channel to the UK via boat hulls, first being identified in 1994 (Wade, Ames and McKee, n.d.). Globally the species has been identified in South and North America, Scandinavia, and New Zealand, as well as various parts of Europe (NNSS, 2020). 
Today, the species has only been identified once in Scotland, tending to be more concentrated around the English Channel (fig. 2). Its single Scottish sighting was in South Queensferry in 2016 (NBN Atlas, 2024). 

Impact:
Being so prolific, Japanese kelp can quickly outcompete native species once it has become established. For example, Japanese kelp is known to outcompete Oarweed (Laminaria digitata) and Sugar kelp (Saccharina latissimi) (NNSS, 2020). 
Additionally, its ability to grow on any solid substrate means it can be a problem in terms of biofouling. It will happily grow on boat hulls, pontoons, rope, buoys, etc (NNSS, 2019), potentially interfering with their function and wracking up significant cleaning costs (NNSS, 2020). 
However, it has also been found to bring some moderate benefits, acting as habitat for various marine species (Oakley, 2007). 

Controls: 
Epstein and Smale (2017) found no management techniques currently employed in the UK and Ireland to prevent the spread of Japanese Kelp. Other countries, such as Australia and New Zealand, use techniques like ballast water management, public awareness campaigns and monitoring for potential infestations (Epstein and Smale, 2017). 
While not actively removed in the UK, the species is listed under the Wildlife and Countryside Act 1981, meaning it is illegal to encourage or allow its growth in the wild (Wade, Ames and McKee (n.d.).