Integrative Barcoding of Freshwater Invertebrates

Abstract

Freshwater invertebrates -- including EPT (Ephemeroptera, Plecoptera, Trichoptera) insects, chironomid midges, oligochaetes, and molluscs -- are the primary biological indicators used in the EU Water Framework Directive bioassessment of river ecological status, yet their identification by traditional morphological methods is increasingly limited by the shortage of specialist taxonomic expertise and the inability to differentiate cryptic species complexes. This study applied integrative barcoding -- combining COI and 16S rRNA markers with morphological examination and, for a subset, ITS2 sequencing and scanning electron microscopy -- to 2,840 freshwater invertebrate specimens from 184 species across 42 Central European river and stream sites (Austria, Switzerland, Germany; 2021-2024). Barcode gap analysis confirmed well-defined COI species boundaries in 164 of 184 morphospecies (89.1%), with a mean 11.4-fold barcode gap. Twenty morphospecies were resolved as cryptic species complexes by integrative analysis, yielding 224 species total -- a 21.7% increase over morphology alone. Among the cryptic complexes, 12 showed ecologically differentiated habitat preferences (different current velocity or substrate preferences confirmed by co-occurrence analysis), with direct implications for WFD bioassessment accuracy: three pairs of cryptic species showed contrasting sensitivity scores in the Austrian ASTERICS bioassessment system, such that misidentification would systematically bias ecological status assessments at sites where both cryptic species co-occur. A Rapid Integrative Barcoding Protocol (RIBP) combining single-tube multiplex PCR (COI + 16S) with nanopore sequencing achieves species identification turnaround of 8 hours from sample to result at EUR 3.84 per specimen -- enabling routine application in national WFD monitoring programmes. Submission of all 2,840 sequences to BOLD Systems creates the most comprehensive Central European freshwater invertebrate barcode reference library to date.