Aquatic Insect Emergence From Benthic and Subsurface Zones via Diverse Riverscape Features in a Gravel‐Bed River

ABSTRACT The hyporheic zone extends beneath active river channels and gravel bars, serving as crucial habitats for invertebrates, including aquatic insects. This study investigated the emergence of aquatic insects from benthic and subsurface zones through the diverse riverscape features of a gravel‐bed river. Insect emergence during the peak period for hyporheic species, from May to July 2024, was surveyed along a 50‐m section of a gravel bar on the Satsunai River in northern Japan. Emergence traps were positioned above water (WS), at the gravel‐bar edge (GE), and on the gravel‐bar surface (GB) to collect adult insects. Larval communities were sampled from the river channel and subsurface hyporheic pipes in GB to ascertain the insects' habitat affinity for benthic and hyporheic zones. Two Plecoptera taxa, Leuctridae spp. and Alloperla ishikariana , predominated in the hyporheic community (94%), whereas the benthic community comprised a more diverse array of taxa, including Ephemeroptera (74.6%) and Trichoptera (12.3%), based on larval data. Total insect emergence was adjusted for the areal extents of WS, GE, and GB; hyporheic taxa dominated GB (70%) and GE (60%), while benthic taxa dominated WS (82%). Hyporheic taxa utilized gravel‐bar GB and GE for emergence disproportionately more than benthic taxa, likely due to the proximity of their larval habitats beneath the gravel bar and the emergence behavior of dominant Plecoptera by crawling onto land. This study demonstrated insect emergence through three distinct pathways mediated by larval habitats in benthic and hyporheic zones and underscored the critical roles of three riverscape features in supporting the reproduction and biodiversity of aquatic insects in gravel‐bed rivers.