Ecological implications of motorboat noise on coral reef fish communities

Abstract

Anthropogenic noise is recognised as a major pollutant of international concern. Motorised vessels are the dominant source of anthropogenic noise in the marine environment. Small motorboats are widespread among coastal regions, exposing shallow marine ecosystems to noise disturbance. Short-term exposure to motorboat noise can have a profound impact on fish physiology and behaviour. However, it remains unclear how such impacts translate to wild fish assemblages. No study has yet investigated the community-wide implications of motorboat noise. The aim of this thesis is to review the current understanding of motorboat noise on fish ecology; provide the first assessment of chronic motorboat noise on a wild fish community; and consider future directions in research, management and mitigation. Using existing spatial variation in motorboat traffic across coral reefs in French Polynesia we carried out visual census techniques to investigate the effect of chronic motorboat noise on a coral reef fish community. In addition, we conducted a month-long motorboat manipulation of a coral reef with minimal disturbance history to test whether community responses can be experimentally induced. There was no difference in the overall fish abundance, species richness and diversity on coral reefs exposed to chronic motorboat noise. Yet, 5 species had significantly lower abundances, whilst 8 species had significantly greater abundances on reef exposed to chronic motorboat noise, resulting in a significant difference in the overall community composition. In addition, the month-long motorboat manipulation replicated the same response in two species as the previous study; though this was not enough to significantly alter the community composition. This study demonstrates that fish species respond differently to chronic motorboat noise, and community implications are more complex than previously predicted. Future studies should consider the diversity of functional traits, noise tolerance and interspecific interactions when investigating the ecological implications of motorboat noise on fishes.