The Chilean Fjords and Channels ecoregion presents unique oceanographic conditions that are sensitive to environmental impacts and socio-ecological systems. To assess how these impacts affect these ecosystems, it is essential to examine the current status of highly diverse taxa, such as molluscs, in terms of biodiversity and abundance, as they serve as valuable macroecological indicators of marine ecosystem health. On the south-eastern margin of the Brunswick Peninsula, south of Punta Santa Ana, lies Cape Froward, where a system of eight small bays (< ca. 4 km²) is located, some of which are used as temporary harbours during navigation. Despite previous sampling efforts and existing records, these areas remain poorly described, with the region around Punta Santa Ana Bay being the most extensively documented. As part of monitoring programmes on coastal biodiversity in Magallanes and fishery resource assessments, sublittoral sampling was conducted in Bougainville Bay using autonomous diving (20 m depth) and a modified Agassiz trawl (44 m depth). This study recorded 49 operational taxonomic units, comprising 32 gastropods, nine bivalves and eight polyplacophorans, all of which represent previously unpublished diversity records for this Bay. Additionally, these species were categorised, based on their feeding strategies, providing insights into their ecological roles. These findings also extend to neighbouring bays along the southern Brunswick Peninsula (from El Águila Bay to Cape Froward), where only two sublittoral species — the bivalves Zygochlamys patagonica and Philobrya sublaevis — had been previously documented. In the central micro-basin of the Strait of Magellan (from Second Narrows to Carlos III Island), this study introduces six new records: one bivalve and five gastropods, including two nudibranchs. All findings were compared with data from the Global Biodiversity Information Facility. These newly-documented records are crucial for understanding the biodiversity of molluscs inhabiting frequently navigated maritime areas, serving as indicators of anthropogenic impacts. This is especially relevant given the recent proposal of the area as a National Park.
