Large-scale monitoring of freshwater bivalves: an eDNA point of view on
species distribution and conservation
Abstract
The analysis of environmental DNA (eDNA) allows efficient surveys of
freshwater species and is being increasingly used. However, most studies
generally have a limited sampling plan. Because different methods are
used by different authors, all the data produced with eDNA cannot be
easily pooled together for a global overview. Nevertheless, one of the
promising perspectives is the standardization of the methods and
protocols, for long-term monitoring, early detection of invasive
species, and rare species detection. We here present the biggest dataset
using eDNA metabarcoding with standardized methods for freshwater
bivalves. Sampling was performed mainly in France, with over 350
localities spread over all major basins. Metabarcoding was performed
using two new sets of primers, one for the Unionida and one for the
Venerida. The species distributions inferred from eDNA sampling are then
compared with those currently known. Results give an insight into the
valuable data that eDNA analysis can provide if used at a large scale.
Some species were found outside of their known range, especially
invasive species but also species of conservation interest. Others were
found in a surprisingly low number of localities, although currently
considered widespread and of no conservation interest. This can be
explained by the databases currently used to establish conservation
status, which are often biased by including ancient data, shell-only
data, and potentially misidentified species. The present study shows
that our eDNA metabarcoding approach will be an essential tool to unveil
the true species distributions, to better evaluate their status and
improve conservation policymaking.