Range edge shifts over time
Species’ range edge shifts differed substantially, ranging from 24.5 km/year (equatorward edge of Homarus americanus in the Northeast) to -26.5 km/year (poleward edge of Sebastes semicinctus in the West Coast). Single-species edge positions over time are reported in Appendix 3. When pooled over all species in a region, all regions had a generally northward shift. Range edges shifted 3.9 km/year in the Northeast from 1967-2018 (90% CI 3.6 – 4.2), 5.2 km/year on the West Coast from 1976-2018 (90% CI 4.2 – 6.2), and 0.1 km/year in the Eastern Bering Sea from 1988-2018 (90% CI -0.2 – 0.4; means and credible intervals from single-species Bayesian linear regressions). Separating these posterior distributions by range edge type (poleward or equatorward) revealed opposing shifts in the two groups: equatorward range edges overall shifted 5.3 km/year (90% CI 5.0 – 5.6), but poleward range edges shifted -2.2 km/year (90% CI -2.6 – -1.8; means and credible intervals from single-species Bayesian linear regressions).
The magnitude of range edge shifts was slightly greater in fishes than in invertebrates. When both were pooled across all species and regions, fishes shifted north 2.6 km/year (90% CI 2.3 – 2.9) and invertebrates 1.7 km/year (90% CI 1.3 – 2.1; means and credible intervals from single-species Bayesian linear regressions). This difference in magnitude of shift was driven by equatorward range edges of fishes shifting faster—6.0 km/year versus 4.0 km/year—than invertebrates (90% CIs 5.6 – 6.4 and 3.6 – 4.4, respectively), while both groups of poleward edges shifted in the opposite direction at similar rates (fishes -2.3 km/year, 90% CI -2.8 – -1.7, invertebrates -2.0 km/year, 90% CI -2.7 – -1.3; means and credible intervals from single-species Bayesian linear regressions).