Ory D. auteur aut IRD Gravier-Bonnet N. auteur aut IRD Chabanet Pascale auteur aut IRD Bourmaud C. A. F. auteur aut IRD Boissin E. auteur aut IRD text journalArticle eng text/pdf born digital access In the context of coral reef decline, mesophotic coral ecosystems (MCEs, 30-150 m) offer hope for the recovery of degraded euphotic reefs. The Deep Reef Refuge Hypothesis (DRRH) postulates the potential of mesophotic reefs to reseed euphotic reefs. This hypothesis needs to be further tested by estimating connectivity along the depth gradient. Mesophotic data are lacking worldwide, particularly in the southwestern Indian Ocean (SWIO). Here, using a total of 2218 samples collected at depths ranging from 10 to 103 m, we estimated the connectivity of 7 hydroid species sampled at euphotic, upper, and lower mesophotic depths around Reunion Island using a multi-species comparative framework. Population genetic analyses using 8-17 microsatellite markers per species (80 markers in total) as well as Bayesian inference were performed to estimate population structure and contemporary migration rates to highlight connectivity patterns and directionality of gene flow between depths. The results revealed three main genetic patterns depending on the species: a horizontal stepping stone pattern between areas around the island, a vertical stepping stone pattern between adjacent depths, and a quasi-panmictic pattern. Each species showed some specificity within these patterns, but overall, at least 4 of the 7 species support the assumption of vertical connectivity from the Deep Reef Refuge Hypothesis, highlighting the importance of studying multiple species. The existence of vertical connectivity between euphotic and mesophotic depths in the southwestern Indian Ocean confirms the importance of mesophotic coral ecosystems for conservation efforts and our global understanding of coral reef ecosystem dynamics. specialized cryptic species isolation by distance microsatellite marker population genetics southwestern Indian Ocean vertical connectivity REUNION OCEAN INDIEN 082 036 020 [Early access] e70089 [21 p.] 2025 0962-1083 https://www.documentation.ird.fr/hor/fdi:010094890 10.1111/mec.70089 0962-1083 [F B010094890] https://www.documentation.ird.fr/hor/fdi:010094890 https://www.documentation.ird.fr/intranet/publi/2025-10/010094890.pdf Accès réservé (Intranet de l'IRD) IRD - Base Horizon / Pleins textes 2025-10-29 2025-11-04 fdi:010094890 fre