Plastic foraging behaviour of a marine top predator CAVALLOCATHERINE ROSE 2019 Interactions between predators and prey are difficult to investigate in marine environments, but it is important to understand these relationships to conserve biodiversity and ecosystems. In particular, the flexible foraging strategies of some predators make it difficult to identify responses to prey variability. I studied the flexible diet, hunting success and predatory effort of little penguins to investigate food web relationships in coastal environments. I extended the known little penguin diet to include sea jellies, defining a new food web link, and produced penguin-derived measures of prey availability. These findings enhance the capacity of marine predators to inform ecosystem management.