Biodiversity and spatial variation of subtidal rocky bottom communities in the west section of the Magellan Strait, Chile

The complex hydrography and coastal geomorphology of the Magellan region in Chilean Patagonia support a highly diverse yet largely unexplored benthic community. Establishing a baseline is essential for detecting future ecological change and informing conservation strategies. This study examines the spatial distribution of subtidal benthic communities in the Strait of Magellan. Megabenthic invertebrates were characterized across five localities along a depth gradient (5, 10, 15 and 20 m) using underwater photoquadrats. A total of 64 species were identified. PERMANOVA revealed no significant differences in community composition across depth, although species richness increased with depth. In contrast, significant differences were detected among localities, with Bell Bay showing the most distinct assemblage, largely driven by Arossia henryae (SIMPER). The high abundance of sessile species, including A. henryae, Magellania venosa, Didemnum studeri, Errina antarctica and Psolus sp., highlights the role of suspension feeders as ecosystem engineers that enhance habitat complexity and biodiversity. Cape San Isidro exhibited reduced sessile cover and extensive bare substrate, likely associated with environmental constraints. No clear depth-related pattern was observed for vagile species. These results emphasize the need to conserve these vulnerable subtidal habitats..