This study reports the first record of microplastics in the stomach contents of the king crab Lithodes santolla. Samples were collected in Nassau Bay during September 2017. Plastics ingested belonged to small microplastics between 3.0 and more than 20 mm long having mainly blue color. Their frequency of occurrence in stomachs was 27%. The microplastic ingestion by L. santolla may present not only a risk for the species self, also for other trophic levels in the food web.

Understanding the ecological implications of species coexistence is central to biodiversity studies and to identify environmental and anthropogenic drivers of ecosystem dynamics, where ecological network analysis offers valuable insights. This study examines the complexity, structure, and potential responses to disturbances of the Strait of Magellan's topological food web. Based on a dataset of 438 predator–prey interactions among 139 trophic species (nodes), the food web was characterized using a two‐scale approach. At the network level, descriptors including connectance, degree distribution, and small‐world pattern, were used to evaluate overall architecture. At the node level, species' roles were assessed using degree, betweenness, closeness, condensed in a novel Keystone Species Index (KSI), and topological role. Potential resilience to ongoing perturbations was inferred by relating these network‐ and node‐level properties. Overall, the network exhibits low connectance and an asymmetrical degree distribution, with a few species concentrating most interactions. Its small‐world pattern, characterized by high clustering and short path lengths, suggests that local disturbances could propagate rapidly. More than half of the species are omnivorous, potentially buffering the system against fluctuations in prey availability. According to the KSI antopological role results, polychaetes, Fuegian sprat Sprattus fuegensis ‘sardina fueguina', and Patagonian blenny Eleginops maclovinus ‘róbalo patagónico', act as central conduits for matter and energy flow, linking benthic and pelagic production to higher trophic levels. The combination of low connectance, an asymmetric degree distribution, and small‐world properties suggests that the food web is fragile to perturbations affecting highly connected species, with the potential to trigger trophic cascades. These findings highlight the importance of understanding trophic interactions for effective conservation and ecosystem management and provide new insights for the Strait of Magellan's ecosystem.

The southern king crab Lithodes santolla is one of the most economically important fishery species in the southern waters of the Atlantic and Pacific Oceans. A combination of stomach content and stable isotope analyses was used to reveal the potential dietary characteristics, isotopic niche, overlap among maturity stages and sexes, and trophic relationships of an L. santolla population in the Nassau Bay, Cape Horn region. Stable isotope analyses indicated that L. santolla assimilated energy from a basal carbon source, the giant kelp Macrocystis pyrifera, forming the trophic baseline of the benthic food web. Moreover, the trophic position of L. santolla varied among late juveniles and adults, suggesting that the southern king crab does undergo an ontogenetic diet shift. L. santolla exhibited intraspecific isotopic niche variation, reflecting niche differentiation which allows the species to partition resources. The trophic relationships of L. santolla with the associated fauna suggested some potential interactions for food resources/habitat use when they are limited. This study is the first attempt to characterize the trophic dynamics of the southern king crab in the Cape Horn area and, by generating more data, contributes to the conservation of the king crab population and the long-term management of local fisheries that rely on this resource.