Freshwater connectivity transforms spatially integrated signals of biodiversity

Aquatic ecosystems offer a continuum of water flow from headwater streams
to inland lakes and coastal marine systems. This spatial connectivity
influences the structure, function and dynamics of aquatic communities,
which are among the most threatened and degraded on earth. Here, we
determine the spatial resolution of eDNA in dendritic freshwater networks,
which we use as a model for connected metacommunities. Our intensive
sampling campaign comprised over 430 eDNA samples across 21 connected
lakes, allowing us to analyse detections at a variety of scales, from
different habitats within a lake to entire lake networks. We found strong
signals of within-lake variation in eDNA distribution reflective of
typical habitat use by both fish and zooplankton. Most importantly, we
also found that connecting channels between lakes resulted in an
accumulation of downstream eDNA detections in lakes with a higher number
of inflows, and as networks increased in length. Environmental DNA
achieves biodiversity surveys in these habitats in a high-throughput,
spatially integrated way. These findings have profound implications for
the interpretation of eDNA detections in aquatic ecosystems in
global-scale biodiversity monitoring observations.