How to read an eDNA species report

The species list

The centerpiece is a table of species, usually grouped by taxonomic class. Each row has a name, a match score, and often a read count or relative abundance estimate.

Common regional species with high match scores are the easy part — treat them as reliable. The value of a good report is in how it flags the interesting rest.

Match score

Match score is how closely your sequence matched the reference. 99–100% is essentially a lock. 97–99% is a strong species-level identification. 95–97% often means the barcode places the sample confidently in a genus but not to species. Below 95% usually resolves only to family.

A hit reported as 'genus' rather than 'species' is not a defect. It is the honest answer when the barcode data cannot distinguish sister species.

Read count and abundance

Read count is how many sequences matched a species after quality filtering. Higher counts generally mean more DNA in the sample, which usually means more biomass or more recent presence — but the relationship is not perfectly linear.

Treat abundance as ranked rather than absolute: 'this species left more DNA in the sample than that species,' not 'there are 47 of these.'

The interesting hits

Watch for three categories: species you did not expect but that make sense (unrecorded neighbors), species that are locally rare or in decline (real ecological news), and species that seem impossible for the region (probable false positives worth investigating).

A good analyst will annotate each of these rather than presenting them undifferentiated in a bare table.

What is not in the list

Absence is weaker than presence. A species missing from one sample is not proof it does not live nearby — repeat sampling over seasons builds the case. Use absence as a hypothesis to test, not a verdict.

Frequently asked questions