Predator-prey dynamics in Sydney Harbour: five millennia of naticid predation

Predation shapes communities by altering the relative abundances of species and the flow of energy through the food web. The structure of food webs and predator-prey interactions are vulnerable to anthropogenic disturbances, particularly in high-density urbanised environments such as estuaries. Drill holes in mollusc shells provide evidence of predation by gastropods on their prey. They can therefore be used to measure predation frequency and how predation frequency may have changed over time. This study quantifies the intensity of drilling predation in the three most common bivalve species (Callista disrupta, Chioneryx cardioides, and Fulvia tenuicostata) in Sydney Harbour over the last 5 thousand years in the context of European colonisation. Surficial death assemblage drilling frequencies are also compared to a global compilation of drilling frequency studies, which indicate that the drilling frequencies in Sydney Harbour are similar to other locations in terms of the overall magnitude of predation and the variation amongst taxa at a site. Drilling predation is an important control within the molluscan community of Sydney Harbour, with 30-70% of individuals drilled over the last 5ka. During the time period that includes the European colonisation and subsequent urbanisation Fulvia drilling frequency declines to approximately half the pre-colonial predation rate. However, Callista and Chioneryx record a consistent drilling frequency over the past ~2,000 years. This suggests that the European colonisation of Sydney had species specific impacts on gastropod-bivalve predator-prey interactions.