The ecology, impact and management feasibility of the invasive kelp Undaria pinnatifida in the UK

The invasive kelp Undaria pinnatifda has a global non-native range and is considered oneof the “world's worst invasive species". It has been present in the UK for at least 25 years;however given its status, there remains a dearth of information regarding its ecology,impacts and management feasibility. A variety of surveys and manipulative techniqueswere implemented in rocky reefs and marinas of the southwest UK to better supportthe design and prioritisation of management, and to advance ecological understandingof marine invasive species more generally. This thesis consistently highlighted thatmarinas are paramount to the successful spread, proliferation and reproductive fitnessof Undaria. Excluding or limiting its abundance in marinas may, therefore, restrictthe likelihood of its spread to new regions and its proliferation to surrounding naturalhabitats. Management feasibility, however, was considered to be low, due to targetedremoval measures in marinas altering recruitment patterns and even promoting totalrecruitment, and the high inter-habitat and inter-annual variation recorded in Undariapopulation dynamics. Within natural rocky reef habitats, Undaria was absent or foundin low abundance in areas of high wave exposure, high desiccation stress, and where therewas high abundance of the native perennial Laminaria spp.. Undaria is therefore likelyto be restricted in the potential range into which it can proliferate. Where Undaria hadinvaded rocky reef communities, there was a consistent and significant impact upon thenative annual canopy-forming macroalgae S. polyschides. The overall ecosystem impactof Undaria on rocky reef communities of the UK, however, is likely to be small, withno consistent impacts identified for any other macroalgal species, including the canopydominant Laminaria spp.. There are cases where targeted management of Undaria maybe proportionate and feasible; however, in many locations around the UK, Undaria islikely to remain unmanaged and will become an accepted part of the biota. How scienceand policy reacts to the continued spread and proliferation of Undaria may influe