Eco-acoustics of coral reefs
Ocean is far from a silent world
In addition to sounds produced by fish and other marine organisms (biophony), habitats are also composed of sounds produced by wind, waves and other geological events (geophony) and sounds produced by human activities (anthropophony). All these sources shape the specific acoustic landscape (soundscape) of different environments. Soundscapes reflect the type of substrate, its state but also the biological activity of organisms.
In collaboration with the USR 3278 CRIOBE of Moorea in French Polynesia, I was interested in the description of soundscapes in order to develop monitoring tools.
The recording of 5 different habitats within the lagoon, sometimes very close geographically (less than 1 Km), revealed specific spectral signatures. These acoustic specificities can thus provide clues to species using sound signals to orient and colonize the reef. The description of deep habitat soundscapes (up to 100m) also revealed differences that could be related to the composition of fish communities they support.
Sounds as monitoring tool for biodiversity and conservation
Soundscapes thus allow the characterization of biotopes and their long-term monitoring. We collected data on 8 sites located on the north coast of Moorea (4 marine protected areas and 4 unprotected areas) to study the diversity and phenology of acoustic activity. The results highlighted daily variations in average sound intensity and acoustic complexity. The average sound level was significantly higher during the night, corresponding to an increase in biological activity, and decreased at sunrise. The average loudness of the sites was positively correlated with the percentage of coral cover. Similarly, acoustic complexity showed a daily variation with higher daytime than nighttime values, suggesting more sources and activity. This acoustic complexity was found to be positively correlated with the number of fish species present as well as with the Shannon-Wiener Biodiversity Index applied to the number of fish species. Comparing the results obtained for marine protected areas (MPAs) and nearby non-protected areas (non-MPAs), it appears that an MPA have a higher acoustic activity (noise level and complexity) than the non-MPA zone.
More recently, my research has shown that these acoustic characteristics can also be involved in the orientation and choice of the substrate for the larvae of two species of reef-building corals, Pocillopora damicornis and Acropora cytherea. Coral larvae preferentially settle on encrusting coralline algae (CCA) via chemical mediation. It appears that if this substrate is associated with the sound of a healthy reef (MPA), the larvae will move significantly more toward it than towards a substrate associated with the sound from an unprotected marine area. If this result illustrates the important role of sounds for coral larvae, a second result is worrying. If the preferential substrate (CCA) is associated with boat noise, the larvae avoid it and move to dead CCAs, a non-viable substrate. It is then the resilience and survival of the reefs that will be impacted.
Anthropogenic noise masks natural cues
Thus, it appears that the increase of human activities along the coastline and the degradation of the habitat could constitute an altering source and masking the acoustic indices. Without reliable evidence and the ability to navigate or communicate effectively, it is the diversity and stability of fish populations and the marine environment as a whole that will be affected.
Selection of articles
Bertucci F, Lecchini D, Greeven C, Brooker RM, Minier L, Cordonnier S, René-Trouillefou M & Parmentier E. 2021. Changes to an urban marina soundscape associated with COVID-19 lockdown in Guadeloupe. Environmental Pollution, 289: 117898.
Ferrier-Pagès C, Leal MC, Calado R, Schmid DW, Bertucci F, Lecchini D & Allemand D. 2021. Noise pollution on coral reefs? A yet underestimated threat to coral reef communities. Marine Pollution Bulletin, 165: 112129.
Bertucci F, Guerra AS, Sturny V, Blin E, Tong Sang G & Lecchini D. 2020. A preliminary acoustic evaluation of three sites in the lagoon of Bora Bora, French Polynesia. Environmental Biology of Fishes, 103: 891–902.
Bertucci F, Maratrat K, Berthe C, Besson M, Guerra AS, Raick X, Lerouvreur F, Lecchini D & Parmentier E. 2020. Local sonic activity reveals potential partitioning in a coral reef fish community. Oecologia, 193: 125-134.
Bertucci F, Lecchini D, Gache C, Khalife A, Besson M, Roux N, Berthe C, Sing S, Parmentier E, Nugues MM, Brooker R, Dixson DL & Hedouin L. 2018. Boat noise prevents soundscape-based habitat selection by coral planulae. Scientific Reports, 8: 9283.
Bertucci F, Parmentier E, Berthe C, Besson M, Aubin T, Hawkins AD & Lecchini D. 2017. Snapshot recordings provide a first description of the acoustic signatures of deeper habitats adjacent to coral reefs of Moorea. PeerJ 5: e4019.
Bertucci F, Parmentier E, Lecellier G, Hawkins AD & Lecchini D. 2016. Acoustic indices provide information on the status of coral reefs: an example from Moorea Island in the South Pacific. Sci. Rep., 6, 33326.
Bertucci F, Parmentier E, Berten L, Brooker RM & Lecchini D. 2015. Temporal and spatial comparisons of underwater sound signatures of different reef habitats in Moorea Island, French Polynesia. PLoS ONE, 10(9): e0135733.