Assessment of hydrological barriers effect in river benthic fauna coupled with eDNA metabarcoding monitoring

Abstract

Anthropogenic activities alter the rivers’ hydromorphological characteristics, affecting the ecosystems. River continuum interruption is identified as a principal cause of longitudinal quality variation. Macroinvertebrates, the most common biological quality indicator, are usually coupled with hydromorphological alteration assessment protocols. Environmental DNA (eDNA) metabarcoding is a recent advance in biomonitoring, complementing classical assessment, responding to time and cost-efficiency limitations. This study assesses the hydromorphological effects of two barriers (sluice and rock ramp) in a large Mediterranean modified river on the structure of macroinvertebrate assemblages using the classical method, coupled with eDNA metabarcoding while it further correlates them with the alteration of the riparian zone. Samplings were conducted at three stations for each barrier, one upstream and two downstream, during high and low flow periods. A range of statistical tests were performed for the assemblages’ comparison, the diversity indices and the investigation of spatial and temporal patterns. The findings include differences among communities’ composition for the two approaches with a moderate overlap between eDNA and classical taxonomy. The ramp had lower influence on biota in comparison to the sluice. Regarding the spatial pattern, no significant differences were revealed for both methods, but it could be attributed to the barriers’ operation extent. As for a temporal pattern, there was a difference between the two methods and, while no separation was noted among the sites as a sum, site-specific differences were found. If some problems concerning the taxonomic assignment of ASVs, the sampling methodology and the primers selection are surpassed, eDNA proves a valuable tool.