Coordinating the fight against invasive alien species: 8 years of operational planning in Reunion Island

Invasive alien species (IAS) are acknowledged as one of the major causes of biodiversity loss world-wide, especially in oceanic islands. In Reunion Island, pristine natural habitats cover 30% of the territory, the largest area of intact habitats in the Mascarene Archipelago. To ensure the protection of these habitats and rare species, a national park was establised in 2007, protecting 42% of the is-land's area, and has since been included on UNESCO's 2010 World Heritage List. To tackle biological invasions, an IAS Strategy was developed in Reunion Island in 2010 and implemented in two Opera-tional Control Plans for Invasive Species (2010-2013 and 2014-2017). Here, we used semi-structured interviews, SWOT analyses, workshops and all relevant data and references about biological invasions in Reunion Island to assess the efficiency of these plans. Costs over 8 years amounted to e 20 million and were mainly allocated to control the expansion of IAS. We identified the most important inva-sive species in terrestrial biomes and developed an online public detection platform to enable prompt, practical responses to new invasions on the island. Hence, early detection of the house crow (Corvus splendens) and the African herb dream (Entada rheedii) have allowed their eradication. The efforts of various stakeholders (public institutions, research organizations, universities, associations) is at the heart of the control of IAS in Reunion Island. The diversity of stakeholders allowed work to take place simultaneously on several fronts. Despite significant spending for the island and a strong local effort, biological invasions appear to have increased in many protected areas, causing UNESCO World Heritage to drop their conservation status for the island in 2017. Our findings suggest that the IAS Strategy in Reunion Island should be substantially modified if impacts are to be effectively mitigated. Rather than attempting to operate on all species and in all areas, prioritizing both species and areas and setting goals and monitoring their effectiveness through indicators within a framework of adaptive management is essential. Strengthening regulation to prohibit entry of new species is necessary. A greater proportion of human and financial resources should also be allocated to the control against IAS.