Undaria pinnatifida: on the invasion potential of the commercially important Asian kelp in Europe

Non-native invasive species were the most common driver of species extinctions in the last 500 years and continue impact ecosystems worldwide. Globalization and population growth facilitate their spread and increase native ecosystems' vulnerability. In light of the Climate Crisis, marine primary producers have gained increasing attention – as a potential solution and an impacted group. A marine primary producer that has gained much attention due to its near ubiquitous worldwide spread as an invasive species is the brown macroalga Undaria pinnatifida. Native to East Asia cultivated intensively, it was introduced to Europe in 1972. By 2009, it had spread until The Netherlands. In this study, a new, self-sustaining population of U. pinnatifida was discovered Sylt, Germany, marking its to date (2024) northernmost introduced population. Two strikingly different phenotypes were observed, yet genetic analysis and field observations revealed high similarity and exchange between them. They were distinct from other European and native populations with the population in France (Brittany) the most likely source of the German U. pinnatifida. Experiments demonstrated gametogenesis and better growth under cold conditions of the German gametophyte isolate and resulting sporophytes compared to a native Chinese isolate, indicating a potential cold adaptation. Further studies are required to prove the latter. While U. pinnatifida is currently limited to primarily artificial substrates in the Wadden Sea, its increasing proximity to the rocky shores of Scandinavia raises questions about the likelihood of an establishment there. This spread could only be enabled by human vectors. Intact native communities have shown resilience to invasion by U. pinnatifida in many regions. Therefore, the best counteraction against the spread of U. pinnatifida, invasive species, and their unpredictable impacts is the protection and preservation of native communities that are under threat from Climate Change.