Large benthic rays are increasingly recognised as powerful bioturbators in estuarine ecosystems. Through repeated excavation of foraging pits, they resuspend sediments, redistribute organic matter, and modify redox conditions, processes that can substantially influence nutrient regeneration and nitrogen removal. Yet the direction and magnitude of these effects remain poorly resolved.
We examined how disturbance by the New Zealand eagle ray (Myliobatis tenuicaudatus) alters sediment nitrogen dynamics in Whangateau Harbour across a natural mud-content gradient. Ray disturbance significantly reshaped benthic ecosystem functioning, with sediment characteristics mediating outcomes. Net dinitrogen (N₂) fluxes increased by up to 138% in higher-mud sands, suggesting enhanced nitrogen removal, but declined relative to undisturbed sediments in low-mud areas. Ammonium (NH₄⁺) fluxes also increased (up to 96%), alongside marked changes in microphytobenthic biomass.
These findings demonstrate that sediment context determines bioturbation effects. By directly linking megafaunal behaviour to biogeochemical function, this study underscores how conserving large benthic rays can generate measurable ecosystem-scale impacts.