New insights in benthic biodiversity of the saya de Malha Bank

Abstract

In the South West Indian Ocean, a unique, remote and atypical geomorphological structure, the Saya de Malha Bank, is considered as an underwater 'island' that plays a key role in understanding benthic biodiversity and connectivity processes in the Indian Ocean. In 2022, the Saya de Malha Bank has been explored during the Indian Ocean expedition led by Monaco Explorations. A team of the Muséum national d’Histoire Naturelle (Paris) and collaborators have explored the benthic diversity of the bank by deploying a combination of sampling methods, such as towed gears (dredge, trawl, and sledge) or by scuba-diving (on-sight, brushing and suction device samplings). A total of 81 stations have been sampled, comprising 35 shallow stations on the summit of the bank (19–58 m depth) and 46 stations gaining depth on the flanks of the bank (73–1141 m depth). From these sampling events, a large collection of marine invertebrates, fish and algae has been preserved for taxonomic (morphological and molecular) studies. The inventory of the benthic biodiversity of Saya de Malha is underway, but it is a long-term process. We propose here to focus on the most represented taxonomic groups (algae, molluscs, crustaceans, annelids and fish) by compiling the primary taxonomic data for the diversity metrics and highlighting some discoveries and potential species new to science. Although the inventory is far from complete, these first results emphasize the endemicity of the fauna and flora of the Saya de Malha Bank.