Julieta Kaminsky

Kelp forests are declining worldwide, but Patagonian giant kelp forests ( Macrocystis pyrifera ) appear to have remained stable over the past half-century. Yet, limited historical baselines and ecological knowledge in this remote area constrain our ability to assess change amid increasing human pressures. Here, we report on extensive surveys spanning a fjord-open ocean gradient in northern Patagonia, including five sites previously surveyed in 1972. Adult giant kelp density did not significantly differ between survey periods, and community patterns across the fjord-ocean gradient closely matched historical descriptions: sea urchin grazing dominated kelp forest dynamics at offshore sites, while abiotic forcing and non-consumptive interactions seemed to become increasingly important toward sheltered inner fjord habitats. Despite this apparent stability, we detected clear footprints of human impact. The invasive sea anemone Metridium senile —absent in 1972—now dominates hard substrata at many sheltered sites (up to 88.4% cover), likely competing with native filter feeders. The commercially exploited sea urchin Loxechinus albus declined by 59–90% in abundance and exhibited smaller maximum body sizes, while the historically widespread Pseudechinus magellanicus has largely disappeared. These findings highlight the need for long-term monitoring to understand how ongoing changes may affect ecosystem functioning and services.

Rhodolith/maërl beds are biogenic habitats formed by free-living coralline algae, recognized for their ecological importance and global distribution. Along the Argentine coastline, the published literature lacks visual field documentation of rhodolith/maërl beds, despite historical reports of rhodolith-forming species. Here, we present visual records of a rhodolith/maërl bed in the Argentine Beagle Channel, associated with an extensive Macrocystis pyrifera kelp forest (~150 m from shore). Two perpendicular swimming transects allowed confirmation of a minimum spatial extent exceeding 40 × 40 m (>1600 m²). Underwater imagery reveals continuous rhodolith cover over unconsolidated sediments, highlighting a knowledge gap in the regional distribution of these habitats in southern South America.

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.

The Beagle Channel–Southwestern Atlantic transition represents a dynamically coupled coastal–ocean system where physical forcing and topographic complexity interact to regulate biogeochemical processes. In this study, we investigate how the Sloggett Submarine Canyon modulates nutrient distributions, particulate organic matter (POM) composition and carbon cycling along a shelf–slope–basin continuum within the Yaganes Marine Protected Area. Hydrographic observations, inorganic nutrients, chlorophyll concentrations, elemental stoichiometry (C:N), and stable carbon and nitrogen isotopes (δ13C, δ15N) were analysed along a transect from the Beagle Channel to the deep ocean. The results reveal strong vertical and lateral gradients associated with water-mass structure and canyon topography. Elevated nutrient concentrations and reduced oxygen at depth reflect the influence of Antarctic-derived waters, while surface layers are characterised by higher oxygen and lower nutrient levels linked to biological uptake. Isotopic and stoichiometric signatures indicate that suspended POM is predominantly autochthonous, derived from in situ phytoplankton production. Progressive isotopic depletion and increasing C:N ratios with depth suggest selective remineralisation and redistribution during particle export. Multivariate analysis highlights temperature, chlorophyll and POC:TN ratios as key predictors of δ¹³C variability. These findings are consistent with a system in which submarine canyon dynamics and mesoscale circulation enhance vertical exchange and influence organic matter transformation along the coastal–open ocean transition. The results underscore the importance of incorporating topographically-driven processes into regional carbon cycling frameworks in subantarctic systems.

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.

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.