Japanese Kelp – Undaria pinnatifida 

Also known as 'wakame', Japanese kelp is ranked within Europe’s top 100 most invasive species (NNSS, 2020). Highly adaptable, it can survive anywhere between high tide and 15m deep and in a range of environmental conditions (Oakley, 2007; Wade et al, n.d.). Consequently, the species has spread throughout much of the globe. Japanese kelp reproduces very rapidly via spores that float through the water, and with a growth rate of 1cm per day the species can spread by 100s of meters annually (NBN Atlas, 2024; Wade et al, n.d.). It can grow to around 2m in length, appearing as large wavy leaves with raggedy edges (fig. 1), secured to a solid substrate (Oakley, 2007). 

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 & 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 et al, n.d.). The species then made its way across the English Channel to the UK via boat hulls, first recorded in 1994 (Wade et al, 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 (as of January 2025) was in South Queensferry in 2016 (NBN Atlas, 2024). 

Impacts:
Once Japanese kelp has become established it can quickly outcompete native species such as 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 grow and spread 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). 

Management: 
Epstein and Smale (2017) found no management techniques currently being 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 as a non-native under the Wildlife and Countryside Act 1981 meaning it is illegal to encourage or allow its growth in the wild (Wade et al, n.d.).