Samenvatting
Bioindicator species -- organisms whose presence, abundance, condition, or behaviour reflects the ecological integrity of
the environment they inhabit -- have been a cornerstone of environmental monitoring since Kolkwitz and Marsson's
saprobic system of 1908, yet the rigour with which candidate bioindicators are validated, applied, and reported remains
highly variable across taxonomic groups, environmental media, and regulatory frameworks. This review synthesises 198
primary studies published 2010-2024 examining the selection, validation, and application of animal bioindicator species
across freshwater, terrestrial, and coastal marine ecosystems in European monitoring contexts. We evaluate bioindicator
performance across five dimensions (sensitivity, specificity, practicality, taxonomic accessibility, and regulatory adoption)
for six major taxonomic groups -- macroinvertebrates, fish, amphibians, birds, small mammals, and soil invertebrates --
using a standardised scoring framework applied to 144 validated bioindicator studies. Freshwater macroinvertebrates
retain the strongest overall bioindicator performance profile (composite score 2.64/3.0), underpinned by the EU Water
Framework Directive's Biological Quality Element requirements. Birds demonstrate high sensitivity and public
engagement value but lower specificity for stressor type identification. Amphibians -- particularly Rana and Triturus spp.
-- show exceptional multi-stressor sensitivity but suffer from rapid population declines that compromise indicator
robustness at degraded sites. Emerging approaches -- environmental DNA (eDNA) metabarcoding, passive acoustic
monitoring, and wearable biologger-based behavioural biomarkers -- are evaluated as next-generation bioindicator
platforms. A practical framework for bioindicator selection, validation, and integration into EU environmental assessment reporting is presented.