Medusae (Cnidaria) of Reunion Island (South West Indian Ocean): Diversity, Abundance and Distribution

Diversity. 2025. Vol. 17. No. 10. Article 694.

Bourmaud C. A., Slobodov S., Guilhaumon F., Goy J., Gravier-Bonnet N.

Numerous studies have been conducted on the benthic stages of Medusozoa in Reunion Island, but none on the pelagic stages. This study is the first to investigate the shallow waters of the island for the diversity, abundance, and spatio-temporal distribution of jellyfish. During a one-year survey, samples were collected with a plankton net weekly or biweekly at four sites (two reef/two non-reef) and two depths (10/50 m). Of the 267 samples, 3450 medusae were sorted and 56 species identified. The meroplanktonic Hydroidolina (Antho- and Leptomedusae) were the most diverse (38 species), while the holoplanktonic Trachylinae (13 species) were the most abundant. Hydromedusa species richness was higher at coastal stations than offshore, but similar between reef and non-reef sites. There was no significant variation in species richness or abundance between months or seasons. Including some other catches, the total number of species reached 62. Eight species are new records for the Indian Ocean (all Anthomedusae). Indian Ocean literature references are given in the species list, and some photographs are provided. This initial study, which greatly expands the local hydrozoan fauna knowledge, will serve as a reference for future research, especially regarding climate change and coastal management in Reunion Island.

Keywords: seasonality, Indian Ocean, abundance, Medusozoa, species richness, Hydroidolina, Trachylinae, coral reefs