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).