Sampling locations and assignment to geographic sub-regions.

<p>(A) A map of European Seas with circles representing collection sites for individual samples from the Western Baltic Sea (WBS), the Atlantic and the Baltic Sea regions. WBS and Icelandic samples (part of the Atlantic region) are labeled with light blue and dark blue circles, respectively. (B) Collection sites for individual samples from the North Sea sub-region (NOS; purple), and Baltic Sea sub-regions: Skagerrak-northern Kattegat (SK1; pink), southern Kattegat-Belt Sea 1 (KB1; red), Belt Sea 2 (BES2; orange), Inner Baltic Sea (IBS; green). Borders between SK1 and KB1, and BES2 and IBS (dashed lines) were based on proposed borders between management units at 56.95°N latitude, and 13.5°E longitude, respectively (39). Borders between NOS and SK1, and KB1 and BES2 are based on [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0162792#pone.0162792.ref032" target="_blank">32</a>]. Geographic assignment to regions and sub-regions is summarized in a table (bottom right). Map data: ESRI (2013).