Abstract
Large benthic rays are increasingly recognized as important bioturbators in estuarine systems, yet their influence on nutrient cycling, particularly nitrogen dynamics, remains underexplored. In this study, eagle ray ( Myliobatis tenuicaudatus ) foraging pits were simulated in the Whangateau Harbour, New Zealand, to investigate short-term effects on sediment solute fluxes across a gradient of mud content (1.3–9.9%). Using in-situ chambers, net oxygen (O 2 ), ammonium (NH 4 + ), and dinitrogen (N 2 ) fluxes were measured alongside sediment organic matter content and chlorophyll- a concentration. Multivariate analysis revealed that experimental pits altered sediment ecosystem processes, with mud content modulating the effect. Strongest pit effects were observed in net fluxes of N₂, NH₄⁺ and concentrations of chlorophyll- a . Net N 2 fluxes increased by up to 138% in the experimental pits compared to controls in sands with higher mud content but were lower than the controls in low-mud sands. Net NH₄⁺ fluxes also rose in pits, with increases of 96% in intermediate mud content and 50% in the highest mud group. These findings demonstrate that sediment characteristics like mud content establish the geochemical context in which ray bioturbation acts as a dynamic modifier of net nitrogen fluxes.