Underwater silence world: the end of the dogma

Passive acoustics can offer inexpensive, non-invasive and no-destructive means of assessing temporal and spatial patterns in the distribution of individuals engaging in calling. In marine environments, passive acoustic recording methods can be used at depths not accessible to humans, independent of weather conditions, and for a long term. However, these studies have often restricted their investigations to the monitoring of one or two aquatic species. One reason of this loss of information is quite easy to explain: most of the sounds can be detected but cannot be identified. In many families, calling abilities are described in one or two species only although the descriptions of sound producing mechanisms have highlighted other members should be able to make sounds. Since 50 years, sounds were for example described in more or less 40 pomacentrid species but all the 392 species should be able to make sounds. This situation can be more complicated since some species are able to make different kinds of sounds according to the behavioural context. Some call characteristics can also be modulated according to the size in some species only. It shows an important amount of work has to be done to be able to understand the reef soundscape and to develop call recognition software system.