Global Sensitivity and Uncertainty Analyses of an Ecosystem Model for Simulating Food Web Dynamics in the Cooperation Sea, Southern Ocean

There is growing interest in developing and using ecosystem simulation models to support resource management in the Southern Ocean. However, poor understanding of the impacts of uncertainty in ecosystem model parameters slows down progress towards operational ecosystem models. To address this issue, we explored uncertainty in the parameters estimated during the calibration of an OSMOSE ecosystem model for the Cooperation Sea (“OSMOSE-CooperationSea”) and the impacts of this uncertainty. Our investigations pertained to four types of calibrated parameters: Plank.access, the proportion of the biomass of background species groups available to focal species groups; Bioflux, the flux of migratory species group biomass across the modelled domain boundaries; Mlarval, the larval mortality of the focal species groups; and Mnatural, the additional natural mortality of the focal species groups. Morris method suggested that the community was most sensitive to changes in the Mlarval of mesopelagic fishes. The biomasses of large-size, long-lived species such as toothfishes, Adélie penguin (Pygoscelis adeliae), seals, and whales were most sensitive to the parameters specific to these species groups. By contrast, the biomasses of small-sized, short-lived species such as mesopelagic fishes and krill species were most sensitive to changes in the parameters specific to the predators of these species groups. Monte Carlo simulations showed that community dynamics were more influenced by Mlarval and Mnatural parameters than by Plank.access and Bioflux parameters. The biomasses of Adélie penguin, seals, and whales decreased, while the biomasses of mesopelagic fishes and Antarctic krill increased, after gradually increasing Mlarval or Mnatural. By providing a comprehensive analysis of uncertainty in the parameters estimated during the calibration process, the present study represents an important step towards an operational ecosystem model for supporting ecosystem-based management in the Cooperation Sea. The present study will serve as a valuable basis for similar ecosystem modelling efforts in the Southern Ocean.