Loss of Large Animals Differentially Influences Nutrient Fluxes Across a Heterogeneous Marine Intertidal Soft-Sediment Ecosystem

Abstract

Coastal marine soft-sediment ecosystems profoundly influence nutrient cycling, carbon flows and primary productivity; both the resident animal communities and environmental characteristics can drive the direction and magnitude of fluxes across the sediment–water interface. Coastal and estuarine sedimentary ecosystems are spatially heterogeneous, and many are degrading due to environmental change. How ecosystem function is affected by spatial variation in both habitats and associated animals is critical for understanding the role of specific habitats in ecosystem function and defining the consequence of the functional extinction of species and changes in habitat spatial distributions. In a multi-site field experiment, we tested the effects of spatial variation in benthic communities and environmental characteristics along natural gradients in sediment grain size. We experimentally simulated the depletion of large benthic macrofauna to assess the impact of these functionally important taxa on key ecosystem functions through ammonium and oxygen solute fluxes across the sediment–water interface. The magnitude of change in solute fluxes varied across sites and depletion treatments and was explained by changes in both sediment physico-chemical characteristics and the functional attributes of the benthic community. Quantifying variation in fluxes across multiple habitats provides insight into the trajectory of change and the consequences for ecosystem function at broad spatial scales.