Non-consumptive effects in fish predator–prey interactions on coral reefs

Predator–prey interactions are critical in ecological communities, but it is increasingly clear that a predator’s effect goes beyond eating prey. Fear of predators may also alter the behaviour, physiology, and morphology of prey as they try to reduce risk. Such ‘non-consumptive effects’ (NCEs) may have important demographic effects on prey populations. The study of NCEs has recently grown significantly across marine ecosystems, including coral reefs. Coral reefs support diverse predator assemblages, and consumptive effects substantially impact prey populations, suggesting NCEs are also likely to be important. Indeed, a growing number of aquarium and field studies have demonstrated that the behaviour of reef fishes is changed by predators, typically using predator models or a gradient of fishing pressure. Here, we review these studies to summarise what is currently known about NCEs in reef-fish assemblages, including effects on individuals and populations and variations in space and time caused by predator and prey traits and environmental factors, and the evidence for NCEs driving trophic cascades. Critically, throughout we also draw on a wider literature to highlight hypotheses and theories emerging in other ecosystems that can inform further work on reefs. While it is clear NCEs are significant among reef fishes and can alter reef functioning, evidence of demographic changes, mechanistic pathways (e.g. behavioural vs. stress induced), and work with multiple predators and prey is lacking. We suggest that establishing an initial framework of interactions among different predator and prey types is needed, allowing the integration of factors such as habitat complexity and internal prey state (e.g. hunger), and an increased understanding of how fishes move around seascapes of fear and how to integrate NCEs into ecosystem models. Such integration is critical for a fuller understanding of how fish assemblages function, interact with benthic organisms, and will be affected by environmental stressors.