Environmental DNA (eDNA)

Environmental DNA is genetic material, skin cells, mucus, waste, that organisms shed into water, soil or air, which can be collected and sequenced to detect which species were recently present without ever capturing or observing them directly. A water sample from a lake, for example, can reveal which fish species live in it.

Analysis typically follows one of two paths: targeted assays that test for a single species' DNA using a species-specific primer, useful for confirming presence of an invasive or endangered species, or metabarcoding, which sequences all DNA in a sample and matches fragments against a reference database to build a full species inventory, a form of genomics analysis. This differs from a species distribution model, which predicts where a species could plausibly live from environmental variables; eDNA instead provides direct, if indirect, evidence that it actually was there.

eDNA surveys are increasingly used alongside traditional field surveys in conservation monitoring, biodiversity net gain baseline assessment, and early detection of invasive species, because they are less labor-intensive and can detect rare or elusive organisms that visual surveys miss. Pitfalls include false negatives from degraded or diluted DNA, contamination producing false positives, and reference databases with incomplete species coverage, which limits identification accuracy, especially outside well-studied regions.