Marine trophic architecture and hidden ecological connections in the Strait of Magellan: keystone species and ecosystem resilience

Abstract

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