Habitat Preferences and Distribution of Ephemera orientalis (Ephemeroptera: Ephemeridae) in the Hangang River, South Korea

ABSTRACT

This study characterized the spatial distribution patterns and habitat preference of Ephemera orientalis larvae in the Hangang River based on four surveys conducted in April, June, August, and October 2024. Field surveys were conducted at 10 sites along a 24 km reach, with five cross‐sectional sampling points per site. Larval density varied significantly among sites and points, with consistently higher densities at central channel points. Taylor's power law indicated a strongly aggregated distribution ( b  = 1.66). This pattern coincided with higher substrate size diversity in the central channel (NST; number of distinct grain‐size classes present), and NST showed the strongest positive association with larval density in negative‐binomial GLMMs among the measured environmental variables. Fine‐only substrates (≤ 1 mm) occurred predominantly at riverbanks and supported substantially lower larval densities than all other substrates. In contrast, mixed‐grain patches with coarse particle inclusion were concentrated in the central channel and were consistently associated with higher larval densities. Overall, these results indicate that patch‐scale substrate size diversity is a primary correlate of E. orientalis distribution in the Hangang River, and that larval distribution is better explained by substrate size diversity than by the proportional dominance of any single grain‐size class.