Shallow benthic invertebrate communities in relation to substrate types in coastal environments of the sub-Antarctic Crozet archipelago

Yann Lelièvre^1*Quentin Jossart¹Stéphane Hourdez²Marie Verheye³Andreas Kelch⁴Davide Di Franco⁴Jamie Maxwell⁵Sebastian Rosenfeld⁶Melanie Mackenzie⁷Nicolas Lavesque⁸Erwann Legrand⁹Maria Capa¹⁰Guillermo San Martín¹¹Camille Moreau¹²Thomas Saucede¹

• ¹UMR6282 Biogeosciences, Dijon, France
• ²Laboratoire d'Ecogeochimie des Environnements Benthiques, Banyuls-sur-Mer, France
• ³Universite de Liege, Liège, Belgium
• ⁴Senckenberg Forschungsinstitut und Naturmuseum Frankfurt am Main, Frankfurt, Germany
• ⁵University of Galway, Galway, Ireland
• ⁶Instituto de Biodiversidad de Ecosistemas Antarticos y Subantarticos, Santiago, Chile
• ⁷Museums Victoria, Melbourne, Australia
• ⁸Environnements et Paleoenvironnements Oceaniques et Continentaux, Pessac, France
• ⁹Institute of Marine Research, Nordnesgaten, Bergen, Norway
• ¹⁰Balearic Biodiversity Centre, Palma, Spain
• ¹¹CIBC-UAM, Madrid, Spain
• ¹²Universite Libre de Bruxelles, Brussels, Belgium

Coastal ecosystems of sub-Antarctic islands are threatened by increasing climate-driven changes and direct anthropogenic pressures. Significant effects on marine communities are expected, but benthic ecosystems of these isolated islands remain largely under-explored. Effective preservation of these nearshore environments requires deeper ecological assessments and comprehensive biodiversity knowledge. In this regard, this study reports findings from a survey carried out in 2021 at two sites – Baie du Marin and Crique du Sphinx – located on the eastern coast of Ile de la Possession (sub-Antarctic Crozet archipelago, Southern Ocean). We investigated the composition and structure of nearshore benthic faunal communities using a quantitative fieldwork protocol and an integrative molecular- and morphology-based taxonomic approach. A total of 124 morphotypes were identified, including a high proportion (72%) of rare species. Both sites exhibited similar benthic invertebrate communities. Structurally complex habitats such as hard substrates or areas dominated by macroalgae exhibited higher species richness and diversity. The investigated benthic invertebrate communities are typical of the sub-Antarctic area but featured unique structures, including dense tube-dwelling polychaete colonies. This study will provide a baseline for future monitoring programs and for the preservation of sub-Antarctic coastal benthic ecosystems.