Data from: Using environmental DNA metabarcoding to monitor fish communities in small rivers and large brooks: Insights on the spatial scale of information

Monitoring fish communities is central to the evaluation of ecological
health of rivers. Not only presence/absence of species is important to
assess, but also the species composition of local fish assemblages is a
crucial parameter. Lotic fish communities are traditionally monitored via
electrofishing, characterized by a known limited efficiency and high
survey costs. The use of environmental DNA-based analyses could serve as a
non-destructive alternative, but this approach requires further insights
in practical sampling schemes incorporating transport and dilution of the
eDNA fragments; as well as optimization of molecular detection in terms of
predictive power and quality assurance. By introducing fifteen species
known to occur in Belgian waters via a controlled cage experiment, we aim
to extend the knowledge on streamreach of eDNA in small rivers and large
brooks, as laid out in the European Water Framework Directive’s water
typology. Introducing fish communities in two transects of a species poor
river characterized by contrasting river discharge rates, we found strong
and significant correlations between the eDNA relative abundances and the
relative biomass per species in the cage community. Despite a decreasing
correlation over distance, the underlying community composition remained
stable over a distance of 300 m up to 1 km downstream of the cages,
depending on the river discharge rate. Such decrease in similarity between
relative source biomass and the corresponding eDNA-based community profile
with increasing distance downstream from the source, can partly be
attributed to variation in species-specific eDNA persistence. Our findings
offer novel insights on eDNA behaviour and characterization of riverine
fish communities. We conclude that water sampled from a relatively small
river offers an adequate snapshot of the total fish community composition
occurring within an upstream perimeter ranging between 300 and 1000
meters. The potential application for other river systems is discussed in
this study.