Approaching the Ecological Role of the Squat Lobster (Munida gregaria) and the Fuegian Sprat (Sprattus fuegensis) in the Francisco Coloane Marine Area (Magellan Strait, Chile) Using a Pelagic Food Web Model

SIMPLE SUMMARY: We investigated the ecological role of the squat lobster (Munida gregaria) and the Fuegian sprat (Sprattus fuegensis) in the food web of the Francisco Coloane Marine Area in the Magellan Strait, Chile. We analyzed the ecosystem impacts of biomass changes in the squat lobster and Fuegian sprat. Food web indicators and simulations were estimated using the Ecopath with Ecosim software. Both species were located in the second trophic level. The squat lobster was preyed upon by 12 functional groups, which highlighted its role as an important prey in the ecosystem and its positive impacts on predators such as red cod, whales, and penguins. As prey, the Fuegian sprat presented a direct interaction with 10 functional groups, which exerted positive impacts on predators such as penguins, seabirds and whales. In summary, the Francisco Coloane Area is an immature ecosystem with productivity and energy flows values within those reported for productive ecosystems; the role of the squat lobster seems to be related to the structure of the food web, while the Fuegian sprat plays a role in the energy transfer to top predators. Although the study area is currently a Marine Protected Area, monitoring squat lobster and Fuegian sprat populations might ensure the conservation of this ecosystem. ABSTRACT: The structure and functioning of the food web of the Francisco Coloane Marine Area in the Magellan Strait, Chile, was quantified, with an emphasis on identifying the ecological role of the squat lobster (Munida gregaria) and the Fuegian sprat (Sprattus fuegensis). Food web indicators, the trophic level, and centrality indices were estimated using Ecopath with Ecosim. Dynamic simulations were carried out to evaluate the ecosystem impacts of biomass changes in squat lobster and Fuegian sprat. The model calculated a total ecosystem biomass of 71.7 t km(−2) and a total primary production of 2450.9 t km(−2) year(−1). Squat lobster and Fuegian sprat were located in specific trophic levels of 2.3 and 2.7, respectively. Squat lobster reduction produced a decrease in the biomass of red cod (42–56%) and humpback whales (25–28%) and Fuegian sprat reduction a decrease in penguins (15–37%) and seabirds (11–34%). The Francisco Coloane Area is an immature ecosystem with productivity and energy flows values within those reported for productive ecosystems; the role of the squat lobster seems to be related to the structure of the food web, and the role of the Fuegian sprat seems to be related to the functioning of the ecosystem and to the energy transfer to top predators.