Undetected non-indigenous species in the Sado estuary (Portugal), a coastal system under the pressure of multiple vectors of introduction

Research effort concerning biological invasions has increased significantly but the pressure of multiple vectors of introduction (MVI) on coastal areas is still poorly understood. The aim of this work is to provide a comprehensive list of non-indigenous species (NIS) occurring in the Sado estuary, identify and prioritize MVI to deliver recommendations for bioinvasions management. Fouling communities were sampled in five artificial systems during 2021 and 2022. Additionally, a thorough literature review was performed to provide a comprehensive NIS database for the Sado estuary. Native distribution of NIS was classified based on biogeographic realms and the most likely pathways and vectors of introduction were assigned to each introduction. A total of 52 NIS were catalogued, predominantly arthropods, 22% of which were reported until 2005, while 40% were recorded in the last 2 years. We also reported four new NIS to Portugal. Most NIS were native from the Temperate Northern Pacific and the Temperate Northern Atlantic. Shipping related vectors were dominant (61%). Aquaculture was not directly linked to many invasions (8%), however contaminants on animals was the second most significant vector (23%). Our results highlight the need for managing MVI in locations that may act as invasion hotspots. Additionally, it provides support for future policy and management measures by identifying areas that are vulnerable to biological invasions. The introduction of NIS is an important driver of changes on biodiversity, and it should be included as a key element for the creation of an integrated management tool for the Sado estuary.