Diel and Artificial Light Effects on Nearshore Communities Revealed by eDNA Metabarcoding

Changes in natural and artificial light presumably have dramatic influences on ecological communities, yet measuring these effects can be challenging due to the difficulty in distinguishing ecological signals from background variability. Here, we used environmental DNA (eDNA) to test for light-associated changes in a nearshore marine community. Over 8 days at Friday Harbor Laboratories, Washington, USA, we sampled seawater at midday and midnight with and without an artificial light treatment, analyzing a total of 84 samples (3 L triplicate samples) using COI and 12S markers on an Oxford Nanopore MinION platform. We detected 229 eukaryotic (COI) and 77 vertebrate (12S) taxa across 11 trophic groups, dominated by primary producers (89 species), benthic invertebrates, and fishes. Metabarcoding captured community restructuring within 30 min, such that we could observe meaningful effects of artificial light treatments at night (particularly among spawning polychaetes), as well as more fundamental community shifts in day vs. night (e.g., with primary producers, gelatinous zooplankton, and filter feeders more common during the day). These techniques offer a means of near-real-time assessment of wholescale changes in ecological communities, and our results here illustrate species- and group-specific effects of light levels that are likely important in structuring nearshore marine communities worldwide.