Who’s yelling? An ichthyological investigation of Polynesian lower mesophotic reefs

Mesophotic coral reefs have unique fish assemblages and a very diverse biophony (i.e.,
sounds generated by all sound-producing organisms in a given habitat). However, most of the emiters of these sounds are unknown. The aims of this study are: (1) to identify which vocal fish species are present in the deep part of mesophotic coral reefs in French Polynesia on the basis of the literature; (2) to infer the sounds produced by the species present to link them with sounds previously recorded; and (3) to identify the sonic structures used by species from these families to make sounds. A total of 42 vocal families were found to be possibly present at 120 m depth. The most abundant vocal families include Serranidae, Lutjanidae, and Scorpaenidae. Some Scorpaenidae lack a swimbladder and have a main sonic muscle made of bundles inserted to the skull, separated by the Baudelot’s ligament, and prolonged by tendons inserted to the vertebrae. This configuration is similar to the one found in temperate species known to produce sounds very similar to the most predominant sound in mesophotic reefs. The studied Serranidae have intercoastal sonic muscles and a swimbladder closely related to the ribs. This configuration could allow them to produce sounds like downsweeps and tonal calls. This study provides first insights on which fish taxa could produce the sounds
recorded in MCEs and which sonic structures they have.