Download files
Abstract
Marine predator-prey interactions are complex and are strongly influenced by the physical and biological environment. Assessing these influences is crucial, as marine habitats are rapidly being altered by human activities. Conventional experiments using exclusion cages have provided valuable insight into predation processes, but often assume some level of predation that is not measured. New video technology can overcome these assumptions, while novel chemical deterrents also exclude and manipulate small predators without introducing artifacts. In nearshore marine systems, artificial light is increasing, while habitat complexity is decreasing. To examine predator-prey interaction under varied regimes of light availability, artificial light was added to natural nights. Artificial light reduced fish abundances, but allowed fish to consume sessile invertebrates as they would during the day. Furthermore, a range of crevice widths were used to explore how habitat complexity alters predator-prey interactions. Compared to medium and large crevices, small crevices provided a refuge for sessile invertebrates by limiting fish access and supported distinct prey assemblages. Body size can influence prey vulnerability, and is limited by the amount of resources that prey allocate to growth. Additionally, consumptive and non-consumptive interactions between meso-predators and larger predators can influence overall predation pressure. Underwater video was used to quantify fish predation on sessile invertebrates of different sizes, and to identify predatory fish species. The main predators, leatherjackets and wrasse, were unable to exclude large ascidians and sponges, which had gained a size refuge. In a separate experiment, a chemical deterrent was used to exclude a common meso-predator in tandem with cages to exclude fish. This provided a novel approach of manipulating large and small predators to quantify their impacts on prey. While fish were unable to exclude barnacles of any size, due to high recruitment, they did reduce the predatory effect of meso-predators. However in the absence of fish, meso-predators reduced barnacle abundances. Combining novel techniques (underwater video and chemical deterrent) with caging experiments provided previously unattainable insights into predator-prey interactions, advancing the knowledge of predator-prey interactions under a variety of abiotic and biotic contexts.