Although mesophotic coral ecosystems account for approximately 80% of coral reefs, they remain largely unexplored due to their challenging accessibility. The acoustic richness within reefs has led scientists to consider passive acoustic monitoring as a reliable method for studying both altiphotic and mesophotic coral reefs. We investigated the relationship between benthic invertebrate sounds (1.5-22.5 kHz), depth, and benthic cover composition, key ecological factors that determine differences between altiphotic and mesophotic reefs. Diel patterns of snaps and peak frequencies were also explored at different depths to assess variations in biorhythms. Acoustic recorders were deployed at 20 m, 60 m, and 120 m depths across six islands in French Polynesia. The results indicated that depth is the primary driver of differences in broadband transient sound (BTS) soundscapes, with sound intensity decreasing as depth increases. At 20-60 m, sounds were louder at night. At 120 m depth, benthic activity rhythms exhibited low or highly variable levels of diel variation, likely a consequence of reduced solar irradiation. On three islands, a peculiar peak in the number of BTS was observed every day between 7 and 9 PM at 120 m, suggesting the presence of cyclic activities of a specific species. Our results support the existence of different invertebrate communities or distinct behaviors, particularly in deep mesophotic reefs. Overall, this study adds to the growing evidence supporting the use of passive acoustic monitoring to describe and understand ecological patterns in mesophotic reefs.
Mesophotic ecosystems (approx. 30-150 m) represent a significant proportion of the world's oceans yet have long remained understudied due to challenges in accessing these deeper depths. Owing to advances in underwater technologies and a growing scientific and management interest, there has been a major expansion in research of both (sub)tropical mesophotic coral ecosystems and temperate mesophotic ecosystems.
A new species of (Teleostei, Pomacentridae) is described from four specimens collected between 95 and 110 m depth in mesophotic coral ecosystems in the Maldives, Indian Ocean. can be distinguished from all of its congeners by the following combination of characters: dorsal-fin rays XIII, 12-13; anal-fin rays II,11-12; pectoral-fin rays 17-18; tubed lateral-line scales 17; gill rakers 7+17-18 = 24-25; pearly white body with a large black marking covering the anterior two-thirds of the anal fin. The closest DNA barcode sequence (5.
Heterogorgia abdita sp. nov. is a newly identified mesophotic octocoral species collected at Tigre shoal off Santa Elena Peninsula (Pacific Costa Rica).
Black corals are key species of marine ecosystems. They can be found in dense aggregations worldwide, but some parts of the world remain totally unexplored. This is the case of the Mesophotic Coral Ecosystem of Mo'orea where the Under the Pole scientific expedition explored mesophotic ecosystems between 60 and 120 m depth and focused on whip black corals.
The distributions of anthozoan corals are undercharacterized due to their wide bathymetric ranges, occurrences in remote locales, and difficulties of identification from morphology alone. Environmental DNA (eDNA) sequencing promises to be a noninvasive strategy to complement conventional approaches for mapping and monitoring the distribution and biodiversity of coral communities. Primers for eDNA metabarcoding have been designed to amplify nuclear and mitochondrial DNA barcodes in shallow scleractinians and mitochondrial in deep-sea octocorals.
