<jats:title>Abstract</jats:title> <jats:p> <jats:italic>Eisenia arborea</jats:italic> has a disjunct distribution along the west coast of North America. We detail the current distribution of <jats:italic>E. arborea</jats:italic> and use long-term records to examine how present-day shifts in <jats:italic>E. arborea</jats:italic> prevalence and abundance in British Columbia (BC), relative to the dominant stipitate kelp <jats:italic>Pterygophora californica</jats:italic>, may be driven by interactions between changing grazing pressure and warming water. We further speculate on how the disjunction of <jats:italic>E. arborea</jats:italic> arose. The ancestor of <jats:italic>E. arborea</jats:italic> likely dispersed from Japan to North America where glaciation disrupted its distribution and speciation occurred<jats:italic>.</jats:italic> As glaciers retreated <jats:italic>E. arborea</jats:italic> likely dispersed into BC from warmer waters in the south and/or expanded from refugia off Vancouver Island and Haida Gwaii. While <jats:italic>E. arborea</jats:italic> is uncommon, our records extend its range into Alaska and Washington State. Along western Vancouver Island, BC, under warming conditions, <jats:italic>E. arborea</jats:italic> prevalence and abundance increased where once-extirpated sea otters (<jats:italic>Enhydra lutris</jats:italic>) removed urchins. Where otters were absent, however, reduced summer wave heights, associated with warming, apparently allowed urchins to graze shallow-water kelps, which declined. We suggest that under warming conditions, sea otters may increase kelp resilience, with <jats:italic>E. arborea</jats:italic> becoming more prevalent in NE Pacific kelp forests.</jats:p>