Acoustics: Coral Reefs

Projet: Underwater silence world: the end of the dogma

Coordinateur: David Lecchini

Période: 2015 /2016

Zone d’Étude: Moorea, Polynésie Française

Résumé: Among the most fragile ecosystems on Earth, which include for example the Poles and primary forests, coral reefs have always been under the spotlight of the society because of their extremely high biodiversity and the services provided to humans such as food supply, protection of the coasts and nutrient cycling. Climate change put coral reefs under several concomitant threats, it is therefore crucial to develop new tools allowing to measure the degradation rate and/or the resilience of coral reefs. This information may be obtained only by the analysis of long time-series, i.e. monitoring, and repeated surveys are always encouraged. The ocean has never been a silent world since sounds are involved in acoustic orientation, intra- and inter-specific communication, to search for prey or to avoid predators and hazards. Currently, we have very little insight into the link between coral reef quality (in terms of biodiversity and substratum cover) and soundscape patterns. Acoustics can offer new visions into the state of biodiversity within marine ecosystems. Understanding how changes in the acoustic environment over time affect marine animals in their distribution pattern, migratory behaviour and acoustic communication appears as a mobilizing topic
The project “Underwater silence world: the end of the dogma” aimed to go beyond the current state of the art by creating a standardized passive acoustic monitoring in order to evaluate the environmental status of coral reefs based on fish vocal activity and peculiar soundscapes features. To reach this objective, Frederic Bertucci was employed one year (in 2015) by Prof. Lecchini (CRIOBE) and Prof. Parmentier (Liege University). He worked at CRIOBE in Moorea from January to August to collect the acoustic and biological data. At present, he is working at the Criobe in Perpignan and at Liege University to analyze the data.

Objective 1: Listening to the reef orchestra: Provide acoustic maps of coral reefs in order to identify spots with high vocal activity and most diverse sound sources. This part of the project was based on a description of marine soundscapes and an identification of sound producing species, the behavioural/social context of production and the localisation of sources at Moorea (on the outer slope of Tiahura site, north coast of Moorea) in order to provide the finest description of the marine score.

Objective 2: Linking the acoustic features of the reef to biodiversity and climate change: Biotic sounds, and especially sounds from vocalizing animals, have a huge potential as proxies to quickly capture the diversity of species, the phenology of biological events, and ultimately the habitat quality and the condition of fish and shellfish stocks. Based on the acoustic signatures and vocalizing species catalogue obtained in objective 1, this second objective associated classical monitoring techniques, used for collecting detailed site-specific oceanographic and biological data, together with passive acoustic data and soundscape analysis. The study was conducted on the outer slope of 4 marine protected areas and 4 non-marine protected areas at Moorea. This will allow detecting peculiar features of soundscapes to inquire about biodiversity and account the potential effects of climate-induced changes in the composition of soundscapes.

Objective 3: Proposing new indices for marine environments: Understanding short-term local effects of environmental fluctuations are important for marine organisms and ecosystems’ management and conservation efforts. However, current acoustic-based indices used for biodiversity assessment and landscape investigation originate from terrestrial ecology studies. They sometimes appear unappropriated when used in the marine environment. This might be due to different sound characteristics like for instance a more narrow frequency bandwidth in fishes (50 – 2500 Hz) than in birds (2000 – 5000 Hz) or mammals (20 – 40000 Hz). Likewise, vocalisations in fishes have a lower signal to noise ratio than most sounds produced in air by birds and mammals. It is therefore important to refine current indices and even develop specific ones to accurately capture underwater animal diversity and include them in decision making with long-term conservation perspectives

Collaborateurs:
- National: Museum National d’Histoires Naturelles, Fondation Grenoble INP
- International: Univ. Liège (Beligium), Univ Delaware (USA), Univ. Aberdeen (Scotland), Univ. Leiden (Natherlands), Univ. Urbino (Italy)

Source de Financement: Fondation Total