Investigating the ecological role of sound on coral reefs
Acoustic environments (soundscapes) are increasingly being recognized for their ecological relevance to marine life. Larval stages of many species use acoustic cues to optimize their choice of settlement habitat. Coral reefs feature particularly complex natural soundscapes, yet little is known about the potential effects of these sounds on coral larvae. Reef soundscapes are also frequently polluted by anthropogenic noise, which can disrupt natural cues and negatively impact sound-sensitive taxa. This thesis aims to fill knowledge gaps in this understudied field of coral reef acoustic ecology by 1) assessing coral larval settlement responses to replayed acoustic cues across multiple species and exposure contexts, and 2) harnessing long-term passive acoustic recordings from protected coral reef sites to understand how anthropogenic noise impacts these vital ecosystems. In laboratory and field-based experiments, I exposed four species of corals (Porites astreoides, Favia fragum, Diploria labyrinthiformis, and Pocillopora damicornis) to playback of reef sounds and documented their settlement responses. I found that playback of healthy reef sounds led to significant increases (~2x on average) in larval settlement rates across coral species exhibiting diverse reproductive strategies of both brooding and broadcast spawning. I documented these responses in field (Chapters 2, 3, 4) and laboratory (Chapters 3, 5) settings. I found that coral settlement responses to sound were species-specific and mediated by experimental variables including distance from the sound source (Chapters 2, 4), larval competency period (Chapters 2, 3), local reef condition (Chapter 4), and acoustic characteristics of playback treatments (Chapter 5). Collectively, these results provide strong evidence that sound is a vital cue widely utilized by settling coral larvae. In Chapter 6, I assessed patterns of boat noise on reefs in the U.S. Virgin Islands from 2019-2020, finding that these reefs are subject to near constant noise pollution, which persisted even throughout the COVID-19 lockdown. This thesis provides new insights into an understudied sensory cue, with important implications for how future stakeholders can harness acoustics to restore and conserve at-risk c oral reef populations.
Coral reefs, Marine larvae, Bioacoustics
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Massachusetts Institute of Technology and Woods Hole Oceanographic Institution