Sample collection
Specimens were derived from ethanol samples, which were collected during diverse monitoring programs or field campaigns and from a copepod culture (Fig. 1, Supplement table 1). Age and storing conditions varied between samples, samples were stored at 4°C from 2018 onwards. Adult female copepods were identified morphologically to species level and stored in ethanol until further processing at 4°C. In total 752 specimens from 32 species and 13 different regions were used for proteomic fingerprinting analyses. Selected samples from the North Sea have been part of the pilot study on using MALDI-TOF MS for species discrimination of North Sea copepods (Laakmann et al., 2013).