Second World Ocean Assessment

Invasion by non-indigenous species (NIS) is a major driver of biodiversity change that can reduce biodiversity, alter community structure and function, diminish fisheries and aquaculture production and impact human health and well-being. It is exacerbated by climate change, including extreme events, and other human-induced disturbances (Bax and others, 2003; MEA, 2005; Ojaveer and others, 2018). NIS are those species, including microbes, that have overcome a natural dispersal barrier to become established in a new biogeographical area outside their native range as an intentional or unintentional result of human-mediated activities (Carlton, 1999). Those species can then spread in the newly invaded area, either naturally or by means of additional human-mediated activities, through a wide range of invasion vectors (i.e., the physical means by which individuals are moved, including biofouling, aquaculture, trade in live specimens and canals) (Carlton and Ruiz, 2005; Richardson and others, 2011). Invasion pathways represent a combination of processes and opportunities that allow individuals to be moved from a source location to a recipient (non-native) one and include some elements of invasion vectors (the term “invasion pathway” has sometimes been used interchangeably with “invasion vector”) (Carlton and Ruiz, 2005; Richardson and others, 2011). Species that undergo distributional changes owing to ecosystem regime shifts or in response to climate change in their native range are not considered to be NIS, and neither are cryptogenic species (those whose native range is unknown) (Carlton, 1996).peer-reviewe