Taxonomic and functional response of estuarine benthic communities to experimental organic enrichment: Consequences for ecosystem function

Abstract

Ecological theory states that the resilience of ecosystem functions to environmental disturbance depends on the biodiversity that underpins them, but field validations of this are rare. In this study, we explore how shifts in the composition of an intertidal macrofauna assemblage following organic matter enrichment affect the representation and composition of functional groups (FG) underpinning sandflat biogeochemistry and stability. Slow-release organic fertiliser was incorporated into experimental plots (1.44 m2) in a gradient study design (treatments ranged from 0 to 2250 g dw m−2). Macrofaunal communities were sampled 70 d later, after changes in sediment conditions associated with organic matter decomposition (hypoxia, acidification and increased concentrations of reduced solutes) had taken effect. Taxa-specific sensitivities to organic enrichment resulted in a significant diversity of responses within FGs, and density compensation was observed in one FG as a result of the disturbance; this enabled FGs to persist even at high levels of enrichment. Despite this, total community abundance decreased by 80% between low and high levels of enrichment and substantial declines in the abundance of dominant taxa reduced the viability of several FGs. Our study demonstrates a density-dependent relationship between macrofaunal biodiversity and ecosystem function, as declines in benthic primary production and nutrient recycling were significantly correlated with decreases in the abundance of key taxa. Despite the occurrence of stabilising mechanisms that provided resilience to FGs, taxonomic diversity was crucial for maintaining ecosystem function.