Expanded records of seagrass distribution and biomass across the Tuamotu Archipelago and Society Islands, French Polynesia

The seagrasses of French Polynesia remain largely undocumented and unmapped, hindering a coherent understanding of their diversity, distribution and potential role in global carbon cycles. We present expanded data from nine sites across six islands and atolls including Bora Bora, Taha’a, Huahine, Moorea, Rangiroa and Fakarava, spanning a distance of more than 680 kilometres. At each location, replicate sites were scoped and new seagrass meadows described for Halophila decipiens and H. ovalis , including leaf morphometrics, seafloor covers (%) and dry weight (DW) biomass (g·m²). The study expands the documented observations of seagrass meadows to a total of 21 across French Polynesia including the first records for Taha’a and Fakarava. Novel data describing differences in leaf morphology of Halophila species and variation in seagrass meadow structure (covers ranging from 1.9% to 47.9%) are presented, along with observations of populations occurring within silty river mouth niches where meadows have not been previously reported within the region. Biomass estimates (ranging from 19.7 to 26 g·m² DW) showed generally greater values in the volcanic Society Islands compared to the Tuamotu Archipelago, though this was modulated by the distribution of species. Our observations expand the documented records of Polynesian seagrass ecosystems and provide new ecological detail for Halophila species across a broad range of Pacific island environments.