Jesse Mosman

Human impacts lead to widespread changes in the abundance, diversity and traits of shark assemblages, altering the functioning of coastal ecosystems. The functional consequences of shark declines are often poorly understood due to the absence of empirical data describing long-term change. We use data from the Queensland Shark Control Program in eastern Australia, which has deployed mesh nets and baited hooks across 80 beaches using standardised methodologies since 1962. We illustrate consistent declines in shark functional richness quantified using both ecological (e.g., feeding, habitat and movement) and morphological (e.g., size, morphology) traits, and this corresponds with declining ecological functioning. We demonstrate a community shift from targeted apex sharks to a greater functional richness of non-target species. Declines in apex shark functional richness and corresponding changes in non-target species may lead to an anthropogenically induced trophic cascade. We suggest that repairing diminished shark populations is crucial for the stability of coastal ecosystems.

Context
Urbanisation is pervasive across landscapes and seascapes and leads to the loss, degradation and fragmentation of many natural ecosystems and this has widespread consequences for animals and the ecological functions they support. While the impacts of urbanisation are understood for many individual coastal ecosystems in isolation, it is unclear how these impacts influence animal assemblages and ecological functions across different coastal ecosystems within the same landscape.
Objectives
We aimed to determine how urbanisation modifies fish and crustacean assemblages and the function of carrion consumption across multiple coastal ecosystems set within the same landscape in eastern Australia.
Methods
We sampled fish and crustacean assemblages in three distinct coastal ecosystems (estuaries, rocky headlands and surf zones) with baited remote underwater video systems and quantified rates of carrion consumption using scavenging assays.
Results
Urbanisation had negative effects on the richness and abundance of coastal fish and crustaceans and the ecological function of carrion consumption, and these impacts were almost always consistent across estuaries, rocky headlands and surf zones. Species richness and abundance were lowest at the most urbanised sites, whereas rates of carrion consumption were lowest at sites closest to urbanised areas, across all ecosystems.
Conclusions
We highlight the negative effects of urbanisation on coastal fish and crustacean assemblages, and a vital ecological function, and the consistency of these effects on distinct coastal ecosystems located within the same landscape. Managing the pervasive impacts of urbanisation on animal assemblages and ecological functions will, therefore, require targeted approaches that address the underlying impacts of urbanisation across multiple coastal ecosystems.