Applicability of environmental DNA metabarcoding for the hyporheic zone of a stream bed

Hyporheic zones play a crucial role in ecological processes primarily orchestrated by hyporheic organisms, known as hyporheos. Our understanding of riverine biodiversity, encompassing hyporheic zones, remains limited. Therefore, the development of a method for the facile and accurate detection of hyporheic communities is imperative. Thus, we evaluated the applicability of environmental DNA (eDNA) metabarcoding surveys in the hyporheic zone in a small stream in Japan. We conducted simultaneous direct sampling and eDNA surveys at two different locations (head and tail of a rapid and a bar) and during two different seasons (less and more disturbed periods). Subsequently, we compared the outcomes of these sampling methods, locations, and seasons. Through eDNA metabarcoding targeting the cytochrome-c oxidase subunit I (COI) regions, we successfully identified a diverse array of hyporheic and benthic taxa in all samples. Remarkably, the performance of eDNA metabarcoding was comparable to the identification of directly sampled benthos and hyporheos. We observed a 62%-78% concordance between direct sampling and eDNA metabarcoding. Notably, eDNA metabarcoding revealed a higher number of hyporheic taxa compared to direct sampling. Moreover, the relative detectability of hyporheos by eDNA metabarcoding differed between the seasons, unlike direct sampling. Our findings underscore the importance of conducting both eDNA surveys and direct sampling to comprehensively assess the composition of the stream community while accounting for seasonal variations. This study demonstrates the utility of eDNA metabarcoding as a non-destructive approach for investigating the hyporheic zone, enabling a more effective assessment of riverine biodiversity.