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

While the invasion of Eurasian cladoceran Bosmina (Eubosmina) coregoni to the Laurentian Great Lakes is well-documented, its spread to the west coast of North America is less understood. We provide evidence that Bosmina (Eubosmina) coregoni 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 B. (E.) coregoni 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 B. (E.) coregoni introduction and improves our understanding of zooplankton invasion dynamics.