The changing song of the sea: soundscapes as indicators and drivers of ecosystem transition on tropical coral reefs

Tropical coral reefs are ecosystems of great beauty and value, but are degrading at unprecedented rates. New approaches are required to monitor and manage reefs worldwide, and to motivate societal changes that reduce the threats facing these vulnerable ecosystems. Healthy coral reefs are alive with sound, as a wide range of soniferous organisms create vibrant soundscapes that reflect the composition of the local community. Many fishes and invertebrates develop as larvae away from reefs before using sound to detect and settle to suitable reef habitat as juveniles, replenishing local populations. In this thesis, I present four field studies that develop and demonstrate the value of bioacoustic approaches to understanding and mediating responses of coral reef ecosystems to degradation. After an introduction to coral reef bioacoustics (Chapter One), I present data showing that soundscapes in the northern Great Barrier Reef have been significantly altered by degradation. Young fishes are less attracted to these post-degradation soundscapes than their pre-degradation equivalents (Chapter Two). Following this, I show that reef recovery can also be measured using acoustic recordings. Previously-damaged reefs restored by rubble stabilisation and coral gardening sound quantifiably similar to nearby healthy reefs and different from nearby degraded reefs (Chapter Three). I then present evidence that loudspeaker playback of healthy reef sound can enhance restoration efforts by increasing fish settlement and retention; fish community development is accelerated by acoustic enrichment of coral-rubble patch reefs compared with unmanipulated controls (Chapter Four). Furthermore, I show that the response of individual species to acoustic enrichment differs in relation to other restoration conditions (Chapter Five). Finally, I discuss the implications of these data for reef monitoring and management, and the use of bioacoustics to inspire public engagement with reef conservation (Chapter Six). In conclusion, bioacoustics offers novel methods to monitor and manage coral reefs, and can motivate people to adopt environmentally-friendly lifestyles. In a world where reefs are changing at unprecedented rates, much can be achieved by learning to listen.