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

Abstract

The invasive kelp Undaria pinnatifda has a global non-native range and is considered one
of 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 techniques
were implemented in rocky reefs and marinas of the southwest UK to better support
the design and prioritisation of management, and to advance ecological understanding
of marine invasive species more generally. This thesis consistently highlighted that
marinas are paramount to the successful spread, proliferation and reproductive fitness
of Undaria. Excluding or limiting its abundance in marinas may, therefore, restrict
the likelihood of its spread to new regions and its proliferation to surrounding natural
habitats. Management feasibility, however, was considered to be low, due to targeted
removal measures in marinas altering recruitment patterns and even promoting total
recruitment, and the high inter-habitat and inter-annual variation recorded in Undaria
population dynamics. Within natural rocky reef habitats, Undaria was absent or found
in low abundance in areas of high wave exposure, high desiccation stress, and where there
was high abundance of the native perennial Laminaria spp.. Undaria is therefore likely
to be restricted in the potential range into which it can proliferate. Where Undaria had
invaded rocky reef communities, there was a consistent and significant impact upon the
native annual canopy-forming macroalgae S. polyschides. The overall ecosystem impact
of Undaria on rocky reef communities of the UK, however, is likely to be small, with
no consistent impacts identified for any other macroalgal species, including the canopy
dominant Laminaria spp.. There are cases where targeted management of Undaria may
be proportionate and feasible; however, in many locations around the UK, Undaria is
likely to remain unmanaged and will become an accepted part of the biota. How science
and policy reacts to the continued spread and proliferation of Undaria may influe

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