| Summary: | International audience Southern Ocean (SO) ecosystems are integral to the Earth System, influencing global climate and biogeochemical cycles. Some SO ecosystems have been heavily exploited and today they are undergoing rapid environmental changes. Theme 6 of the Southern Ocean Observing System (SOOS) aims to understand the impacts of global change on the structure and functioning of SO ecosystems to help inform sustainable management of marine resources. Managers need to distinguish the effects of harvesting from the effects of climate variability and change. Food web models can help to disentangle these interacting effects and to identify the most important biological variables to measure in order to detect changes in ecosystem structure. Extensive biological datasets are available and collection of new data continues under programs such as the Southern Ocean Sentinel and SOOS. These data are being used to develop qualitative and quantitative food web models, which are useful tools for integrating observations from different sources and for testing conceptual models of ecosystem structure and functioning. Quantitative network models provide information on ecosystem structure by identifying the principal pathways of energy transfer from primary producers to top predators. A new generation of end-to-end models couple food web models with biogeochemical models and quantify the contribution of upper trophic levels to nutrient recycling and thus to biogeochemical budgets. Inclusion of variability around model parameters provides a measure of the uncertainty in predictions and could be used in management risk assessment. The Integrated Climate and Ecosystem Dynamics program (ICED) is developing regional food web models based on a generic circumpolar food web structure. These models could provide a framework for comparing the responses of regional ecosystems to common environmental drivers and a basis for linking food web models to larger integrated ecosystem models that include the physics and biogeochemistry of ...
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