Algal resource availability shapes trophic convergence of deposit feeders in a low-turbidity dredged estuary

Dredging alters sediment composition and hydrodynamics, disrupting organic matter distribution and deposit-feeder communities, yet its long-term effects on benthic food webs remain underexplored. We examined how dredging-induced sediment changes influence trophic niches of deposit feeders by analyzing abundance, resource use, and trophic structure of three deposit-feeding species and one predator in Gwangyang Bay, Korea, using stable isotope analysis. Sediment characteristics differed markedly between regions: the northern inner bay was dominated by fine, organic-rich sediments, whereas the dredged main channel contained coarser, organic-poor sediments associated with short water residence times. Despite these contrasts, sediment conditions alone did not explain deposit-feeder distributions; instead, recolonization capacity following disturbance appeared more important. Isotopic niche metrics (δ 13 C range, δ 15 N range, and corrected standard ellipse area) revealed substantial trophic niche overlap among deposit feeders ( Capitella capitata , Magelona japonica , and Theora fragilis ), with primary reliance on phytoplankton and microphytobenthos and minor contributions from riverine and marsh-derived organic matter. Although species-specific traits influenced feeding strategies, high phytoplankton availability likely promoted trophic convergence rather than niche partitioning. Pronounced niche overlap occurred in both dredged and non-dredged areas, indicating that resource availability, rather than sediment conditions, primarily structures benthic trophic interactions. Predatory polychaete, Scoletoma longifolia , occupied a higher trophic position but exhibited similar isotopic overlap across dredged and non-dredged areas, supporting trophic homogenization mediated by shared prey resources. Overall, our results demonstrate that in low-turbidity estuaries such as Gwangyang Bay, autochthonous microalgal availability—rather than dredging status—primarily governs benthic trophic dynamics, underscoring resource-driven controls on trophic structure following dredging. • We assessed the impact of sediment dredging on deposit feeder trophic niches • Isotope data revealed trophic niche overlap among deposit feeders across sites • Phytoplankton availability drove trophic convergence, overriding species traits • Substantial trophic niche overlap occurred between dredged and non-dredged areas • Resource availability, not sediment, shaped benthic trophic structure in the estuary