Urbanisation supplements ecosystem functioning in disturbed estuaries

Abstract

Humans have urbanised and fragmented landscapes across the globe, with detrimental impacts to biodiversity, habitats and food webs in most biomes. Urbanisation might also modify the provision of ecological functions, but these putative effects of landscape transformation are rarely measured. Coastal cities are typically located near estuaries, and we tested for potential impacts of these on ecological functions. Our study used 22 estuaries in eastern Australia as model systems to examine how urbanisation shapes the consumption of carrion by fish, a pivotal ecological function in estuaries. Fish assemblages varied among estuaries according to the extent of shoreline hardening, and this was correlated with changes in the rate of carrion consumption. In estuaries with low levels of shoreline hardening and abundant remnant mangroves, most carrion was consumed by toadfishes (Tetraodontidae). By contrast, in moderately urban estuaries (i.e. where 20–60% of shorelines had been hardened with artificial structures) yellowfin bream (Sparidae) replaced toadfish and performed the bulk of the scavenging function. Bream are particularly effective scavengers that utilize artificial structures as habitat for both foraging and sheltering. We show that by augmenting habitat for an important species of scavenger, the moderate addition of urban structures to estuarine shorelines also helped to supplement a key ecological function in estuaries. Urbanisation impacts diversity in all ecosystems, but many opportunistic species flourish in urban habitats. Identifying and conserving taxa that perform important roles in urban environments is now a critical conservation challenge for maintaining ecological functions across disturbed landscapes.