Aim: We employ a climate-matching method to evaluate potential source regions of freshwater invasive species to an introduced region and their potential secondary spread under historical and future climates.

Location: Global source regions, with primary introductions to the Laurentian Great Lakes and secondary introductions throughout North America

Methods: We conducted a climate-match analysis using the CLIMATE algorithm to estimate global source freshwater ecoregions under historical and future climates with an ensemble of general circulation models for climate change scenario SSP5-8.5. Given existing research, we use a climate match of ≥ 71.7% between ecoregions to indicate climatic conditions that will not inhibit the survival of introduced freshwater organisms. Further, we estimate the secondary spread of freshwater invaders to the ecoregions of North America under historical and future climates.

Results: We identified 54 global freshwater ecoregions with a climate match ≥ 71.7% to the recipient Laurentian Great Lakes under historical climatic conditions and 11 additional ecoregions were predicted to exceed the threshold under climate change. Three of the 11 ecoregions were located in South America, a continent where no matches existed under historical climates and eight were located in the southern United States, southern Europe, Japan, and New Zealand. Further, we identify 34 North American ecoregions of potential secondary spread of freshwater invasions from the Great Lakes under historical climatic conditions, and five ecoregions were predicted to exceed the threshold under climate change.

Main conclusion: We provide a climate-match method that can be employed to assess the sources and spread of freshwater invasions under historical and future climate scenarios. Our climate-match method predicted increases in climate match between the recipient region and several potential source regions, and changes in areas of potential spread under climate change. The identified ecoregions are candidates for detailed biosecurity risk assessments and related management actions. The identified ecoregions are candidates for detailed biosecurity risk assessments and related management actions.

We accessed downscaled historical climate data and climate change projections via the Worldclim database (worldclim.org; Fick and Hijmans 2017). 

Freshwater ecoregion delineations are from Abell et al. (2008).

We used the CLIMATE algorithm (also known as climatch; Pheloung 1996; Crombie et al. 2008) in the provided scripts to model climate match between ecoregions (see article methods for details on which ecoregions).

All scripts are coded in R.