Underwater sampling needs to strike a balance between time-efficient and standardized data that allow comparison with different areas and times. The roving diver survey involves divers meandering and actively searching for species and has been useful for producing fish species lists but has seldom been implemented for benthic taxa. In this study, we used this non-destructive technique to register species associated with kelp forests at the sub-Antarctic Bécasses Island (Beagle Channel, Argentina), detecting numerous species while providing the first multi-taxa inventory for the area, including macroalgae, invertebrates, and fish, with supporting photographs of each observation hosted on the citizen science platform iNaturalist. This research established a timely and cost-effective methodology for surveys with scuba diving in cold waters, promoting the obtention of new records, data sharing, and transparency of the taxonomic curation. Overall, 160 taxa were found, including 41 not reported previously for this area and three records of southernmost distribution. Other studies in nearby areas with extensive sampling efforts arrived at similar richness estimations. Our findings reveal that the roving diver survey using photographs is a good approach for creating inventories of marine species, which will serve for a better understanding of underwater biodiversity and future long-term monitoring to assess the health of kelp environments.

Sub-Antarctic coastal ecosystems are characterized by a high diversity of intertidal and subtidal macroalgae. Recent studies in this region have advanced knowledge of their composition and distribution, as well as adding new species records. During scientific diving expeditions in Isla Grande de Tierra del Fuego, we documented the subtidal brown macroalga Microzonia velutina , representing a new record for Chile and an additional record for Argentina. Field surveys were conducted at three sites, located in Aguirre Bay (Argentina) and Inútil Bay (Chile). Specimens were identified based on external and internal thallus anatomy, following diagnostic criteria established in studies along the Argentine Atlantic coast. The species occurred at depths of 3–6 m in subtidal habitats dominated by giant kelp forests ( Macrocystis pyrifera ). Diagnostic features included a fan-shaped thallus less than 3 cm in size, olive-brown coloration, uniseriate filaments bearing unilocular ovoid sporangia, occurring singly or in clusters. This finding expands the known distribution of M. velutina into sub-Antarctic ecosystems, highlighting Isla Grande de Tierra del Fuego, an important biogeographic region for macroalgal diversity. Future research should investigate the life cycle of the species and apply molecular approaches to clarify its phylogenetic position and evolutionary origins.

The sub-Antarctic region is notable for its high macroalgal diversity. Although a number of studies have documented the species richness of macroalgae along the Chilean sub-Antarctic coast, many regions remain underexplored, with little to no available species inventories or ecological assessments. This study aims to expand current knowledge of macroalgal species richness in the intertidal and subtidal rocky environments in Inútil Bay, a sub-Antarctic area of Tierra del Fuego (Chile). A total of 72 macroalgal taxa were identified: 32 in intertidal and 58 in subtidal habitats. A comprehensive species list is provided, accompanied by photographs of representative macroalgal species.