Managing Risks from Invasive Marine Species: 
Is Post-Border Management Feasible?

Non-indigenous marine species are a major threat to marine environments and economies globally. This thesis examines whether management of pest organisms post-border (i.e, after they have established in New Zealand) is feasible in the marine environment, using the non-indigenous Asian kelp Undaria pinnatifida as a model organism. Background information on Undaria in Chapter 2 recognises the paucity of information on Undaria's impacts. Hence, Chapter 3 investigates ecological effects from Undaria in a low shore rocky habitat. Although negligible effects were described, the uncertainty in extrapolating findings to other places and times means that the precautionary principle should be applied by managers, and 'worst-case' impacts assumed. Chapter 4 investigates mechanisms for Undaria's natural dispersal, and describes strategies based on spore release and sporophyte drift that may lead to spread over scales of metres to kilometres. This work highlights the importance of human transport vectors (especially vessels and aquaculture) in the post-border spread of Undaria at regional and national scales. Hence, a case study in Chapter 5 describes aquaculture activities that could be vectors for spread of Undaria in New Zealand, and presents criteria for identifying present and future high risk pathways. Chapters 6 and 7 describe methods to reduce the accidental transport of Undaria and other biofouling pests with aquaculture, with a focus on mussel farming. Treatments based on water blasting, air drying and freshwater immersion provide low cost options for equipment such as floats and rope. For treatment of mussel seed-stock, immersion in dilute (4%) acetic acid (the active ingredient in vinegar) is identified as a method that could eliminate Undaria and other soft-bodied fouling organisms without resulting in an unacceptable level of mussel mortality. Chapter 8 proposes a risk-based framework for setting post-border management priorities based on the feasibility, benefits and costs of risk reduction. This chapter elucidates how knowledge generated from research in Chapters 2-7 can be used in a biosecurity risk management context. It shows that effective management post-border is possible even when pest organisms become relatively well established, and that the benefits gained from even limited successes have the potential to greatly outweigh the consequences of uncontrolled invasion. However, as unwanted species become increasingly widespread, management will become increasingly focussed on the protection of specific values. Chapter 9 extends some of the ideas proposed in Chapter 8, and considers a broad postborder management framework for marine pests. A comprehensive system should consist of vector management, surveillance, and incursion response that targets particular pests or suites of functionally similar species (e.g., biofouling organisms), coupled with generic vector management approaches that aim to reduce humanmediated transport of all organisms at a national scale. New Zealand's geographic isolation and low population, hence relatively low level of vector activity, makes the management of human-mediated pathways of spread entirely feasible in many circumstances. Hence, while there are clearly many challenges in the post-border management of marine pests, this is nonetheless a realistic goal, and probably moreso in New Zealand than in any other country in the world.