Key areas for krill-mediated carbon sequestration in the Southern Ocean and risk of disturbance by krill fishing

Despite the recognized importance of Antarctic krill in the carbon cycle, in particular in carbon sequestration, around 400,000 tons of krill are harvested each year, potentially hampering the associated carbon sink. Yet, the spatial variability of krill-mediated carbon sequestration is still poorly known since krill biomass is heterogeneously distributed in the Southern Ocean while carbon sequestration efficiency fluctuates with environmental conditions and ocean circulation. Using spatially resolved estimates of krill biomass density and carbon sequestration time, we identified Key Areas for Krill-mediated carbon Sequestration (KAKS) which cover 7,940,290 km² of the Southern Ocean. We found that 30% of krill catches have occurred in these KAKS since 1988. In addition, we identified Conflicting Oceanic Carbon Areas (COCA) with the krill fishery, defined as KAKS that have been intensively fished and that represent around 9% of KAKS over the period 1988 - 2023. When investigating the impacts of krill fishery displacement over the last three decades, we showed that the spatial extent of COCA decreased as the krill fishery aggregated in more restricted areas, while the absolute number of catches, and thus their potential impacts, increased. Furthermore, we found that the CCAMLR Representative System of Marine Protected Areas (RSMPA) is only partially representing the krill-associated carbon sinks with only 3.7% of KAKS currently represented. A new Marine Protected Area (MPA) in the Weddell Sea could significantly increase representation of krill carbon sequestration function as it would be covered at 67% by identified KAKS and would raise the representation level of KAKS to 15%. Finally, we provide recommendations for a carbon-smart management of the krill fishery, as our results aim to inform spatial planning in the Southern Ocean with the dual objective of conserving biodiversity and carbon sinks.