Urbanisation alters processing of marine carrion on sandy beaches

Abstract

Sandy shores are highly attractive for urban development. Urbanisation of beaches is, however, not without environmental consequences, but metrics of ecological change along metropolitan coasts are poorly developed. This lack of metrics impedes environmentally effective coastal zone management. Here we test the effects of urbanisation on a pivotal ecological process on sandy shorelines: carrion removal by vertebrate scavengers. Scavenging is a key process linking ocean and land ecosystems via animal carcasses deposited on beaches and subsequently consumed by mostly terrestrial animals. In this study, experimentally placed fish carcasses were monitored with motion-triggered cameras on urban and rural beaches on the east coast of Australia. Urbanisation substantially influenced the structure of the scavenger guild and the frequency of carrion removal within 24h. Large raptors were abundant on rural beaches where they rapidly detected and consumed carrion (98% of carcasses removed within 24h). We detected no scavenging activity of raptors on urban beaches, where scavenging birds of prey were functionally replaced by nocturnally foraging, non-native mammals (red fox, Vulpes vulpes) or feral species (cats, dogs) known to threaten beach-dwelling wildlife. Our findings emphasise the value of non-urbanised coastal dunes and sandy beaches as important feeding sites and habitats for iconic and threatened raptors. We also show that human changes in coastal land-use profoundly alter ecological structures and processes on sandy shorelines, aspects that warrant explicit inclusion in landscape management and planning of the coastal strip.