Under The Pole Scientific Mission to explore Polynesian reefs: differences between photic and mesophotic fish biophonies: lightning talk

Shallow coral reefs are acoustic hotspots because they are inhabited by many vocal
species. However, few is known on the deeper part of coral reefs, known as Mesophotic Coral
Ecosystems. The aim of this study is to determine how the acoustic fish biodiversity from Polynesian coral reefs vary depending on the depth and the type of island. The link between benthic cover and both the acoustic α-diversity and acoustic fish communities was established using data collected at −20, −60 and −120 m in three atolls (Rangiroa, Raroia and Tikehau) and three high islands (Bora Bora, Mangareva and Moorea). More than 45 fish sound types were found and described. However, these sounds were not found at all depths and at all the islands showing the soundscape can be a signature for the different sites. According to the sound types, the number of some sounds increased with depth while the opposite was observed for others. In most of the islands, acoustic α-diversity fall down between −20 and −60 m but not between −60 and −120 m supporting the existence of a transition zone. A higher acoustic overlap and similarity was found between −60 and −120 m than between −20 and −60 m or between −20 and −120 m. When considering acoustic β-diversity atolls appeared separated from high islands. The diversity was explained mainly by the depth and to a lesser extent by the type of island. The acoustic diversity appeared correlated to benthic cover. A greater variability in the cover at −60 m could increase the reason why a transition fish acoustic community is observed. These results open a potential of Passive Acoustic Monitoring for Mesophotic Coral Ecosystems like it was yet the case with their shallow cousins.