Delineating biogeographic regions in Indian Ocean deep‐sea vents and implications for conservation.

Aim: The pattern of biodiversity and biogeography is crucial to informing management and conservation strategy. But a lack of study across multiple ridge systems, especially for the Carlsberg Ridge, has hampered the conception of the overall picture for the Indian Ocean vents, a top target for deep‐sea exploration of massive sulphides. Here, we aim to characterize fauna from three new vent fields on the Carlsberg Ridge for the first time, and answer 1) what is the biogeographic pattern for vent fauna within the Indian Ocean and 2) how does this pattern guide the future environmental management on the Indian Ocean ridges. Location: Vents on the Carlsberg Ridge (CR), Central Indian Ridge (CIR), and Southwest Indian Ridge (SWIR). Taxon: Macrofauna. Methods: Samples, still images and videos were collected from vent fields by either submersible or TV‐guided grab. A comprehensive dataset of 11 fields on Indian Ocean ridges were obtained based on taxa identification and compilation. Genetic connectivity was analysed for six species using COI sequences. A framework for identifying biogeographic regions based on beta diversity measurement βsim was employed to reveal species turnover along the Indian Ocean ridges. Results: Faunal assemblages at three new vents on the CR hosted a total of 34 species. Significant genetic differentiation was detected between southern SWIR and CIR (plus Tiancheng) for three species, and between CIR (plus Tiancheng) and CR for four species. Hierarchical clustering of βsim support division of the Indian Ocean vents into three clades. Main conclusions: Species turnover along the ridges supported the separation of Indian Ocean vents into three discrete biogeographic units, boundaries between which largely corresponded to genetic breaks for shared species with lower dispersal capabilities. The results clearly show that the conservation of Indian Ocean vents must target three provinces, simultaneously. [ABSTRACT FROM AUTHOR]