From Terra Incognita to ocean sanctuary: a review of scientific insights into the marine diversity of the Crozet Basin and Crozet Plateau

The Crozet archipelago and its adjacent basin—situated within the sub-Antarctic zone of the southwestern Indian Ocean and bounded by the Southwest Indian Ridge—host one of the world’s largest marine protected areas (MPAs), positioning this remote region as a critical focus for pelagic and benthic conservation. Despite its protected status, marine research remains sparse and baseline biological knowledge is still fragmentary. This study presents a comprehensive inventory of marine species compiled from historical expedition reports and contemporary surveys across the Crozet Plateau and Basin. Our synthesis reveals a rich taxonomic diversity, comprising 75 macroalgal taxa and 755 faunal taxa. Notably, 169 species were originally described from this region, primarily from deep-sea environments, underscoring its role as a significant locus for taxonomic discovery. Crucially, the immense scale of this MPA presents severe logistical constraints that leave biological inventories incomplete. These gaps highlight an urgent need for sustained, systematic biodiversity assessments to underpin effective conservation management and climate resilience strategies. As anthropogenic pressures and climate-driven shifts intensify in the Southern Ocean, robust baseline data are essential to inform conservation policy and ensure the long-term sustainability of these fragile, high-value marine ecosystems.