Sedimentary evidence of invasive cladoceran <i>Bosmina (Eubosmina) coregoni</i> presence on the Pacific coast of North America over four decades before first detection

While the invasion of Eurasian cladoceran <i>Bosmina (Eubosmina) coregoni</i> to the Laurentian Great Lakes is well-documented, its spread to the west coast of North America is less understood. We provide evidence that <i>Bosmina (Eubosmina) coregoni</i> was present on the Pacific Coast of North America as early as 1965, ~45 years prior to its first observation in this region in 2008. While investigating dated sediment cores in the Kootenay Lake system, British Columbia, Canada, we found <i>B. (E.) coregoni</i> remains in multiple intervals pre-2008, where it was present in high concentrations (up to 1500 exoskeletons/g dry sediment) and a dominant part of the cladoceran assemblage (25-31.5% relative abundance), though it displayed irregular pulses in abundance. While the method of introduction remains unclear, this research reframes the timeline of <i>B. (E.) coregoni</i> introduction and improves our understanding of zooplankton invasion dynamics.