Increasing Global Expansion Speeds of Marine Invaders

ABSTRACT Aim Quantifying the speed of invasive species range expansion and the mechanisms behind it is a key management goal that also informs ecological theories of spread. Byers et al. found that time since first global introduction (TSI) was the strongest predictor of non‐native range size of coastal marine invertebrates relative to environmental and species traits, and species were predicted to expand on average 400 km/decade along coastlines. Here, one decade later using the same 138 marine invertebrates, we repeat that analysis and test the prediction that the average invader expansion speed was 400 km from 2014 to 2024. Methods Using the Global Biodiversity Information Facility (GBIF), we downloaded species occurrences to estimate the non‐native range size of each invader along coastlines in the northern and southern hemispheres. We calculated expansion speed as the difference between each species' 2024 range size and its 2014 range size estimated by Byers et al. We tested (Hypothesis 1) TSI is still the most important variable for explaining global invasive range size; (Hypothesis 2) Mean expansion speed is 400 km/decade; (Hypothesis 3) Expansion speed is best predicted by distributional characteristics of a species' non‐native range (i.e., initial range size, initial number of coastlines occupied); and (Hypothesis 4) Expansion speeds vary across taxonomic groups. Results TSI was still the best predictor of non‐native range size (RVI = 1, β : 0.39–0.42). However, average range expansion speed since 2014 was 3000 km/decade, ~8× the previous prediction. Species that started with large ranges and distributions across multiple coastlines exhibited the fastest expansion speeds ( R 2 = 0.4), but there were no taxonomic patterns in expansion. Main Conclusions Ranges of non‐native species are not at equilibrium and are still spreading rapidly, posing a challenge for coastal ecosystem management.