Recent history of nonindigenous species in the Laurentian Great Lakes; An update to Mills et al., 1993 (25 years later)

The seminal work of Mills et al. (1993) lists 137 established aquatic species as nonindigenous to the Great Lakes (two plants are further subdivided into two subspecies groups). We have removed seven of these species: three have been redefined as probably native, and four plants (including both subspecies of Sonchus arvensis) have been reclassified as terrestrial. Thirty-five species that arrived prior to 1993 (some due to reclassification, some due to a time lag in discovery and reporting) have been added to the list. Twenty-four new species have become established post-1993, bringing the total to 188 (with Pluchea odorata including two subspecies). Notably, 21 of the 23 species were introduced between 1993 and 2006, but only 3 new species have been documented with new reproducing and overwintering populations in the last decade. Multiple revisions have been made to taxonomy and introduction dates based on additional review of literature and museum/herbarium collections. Over the most recent 25 years, the rate of introduction of nonindigenous species capable of becoming established has declined. With the 2006 expansion of ballast regulations to include residual ballast sediments in vessels declaring 'No Ballast on Board', the rate of new invasions has fallen to a low of only 0.25 species per year. (C) 2019 The Authors. Published by Elsevier B.V. on behalf of International Association for Great Lakes Research.