Mesoscale eddies in the subpolar North Atlantic: their ecological importance and conservation significance

Areas with intense mesoscale eddy activity are often located in international waters and host abundant and biologically diverse ecosystems but these features are not widely protected. Establishing how such areas meet the criteria for proposing international protection requires multidisciplinary and mechanistic approaches. We developed an analytical framework to help identify candidate marine protected areas (MPAs) in regions with mesoscale eddies using the recently designated North Atlantic Current and Evlanov Sea basin MPA in the subpolar frontal zone (SFZ) as a case study. The SFZ has regionally high levels of surface to seabed eddy kinetic energy, high levels of primary productivity, and intense benthic storms. The MPA contains some of the densest deep-scattering layers in the world and > 30 seamounts. Associations between mesoscale eddies and these physical and biological features were evaluated using a framework building multidisciplinary evidence from process-based studies, surveys, and models across multiple scales on phytoplankton and protists to marine megafauna. Implementing this framework revealed that eddies in this MPA directly aggregate and transport diverse and abundant prey items for higher trophic levels especially by structuring deep scattering layers, they support early life stages of key prey such as cephalopods, and they directly influence and positively support threatened and endangered species during migrations, long-range movements and dispersal. Eddy-driven mechanisms interact with other ecosystem processes to achieve benthopelagic coupling, supporting the policy decision to establish an ecologically coherent MPA spanning the ocean surface to the seabed. Mesoscale activity in the MPA is comparable to other global systems, e.g., the Brazil-Malvinas Confluence zone, the Agulhas Current system, and the Kuroshio-Oyashio Extension. While some mechanistic links between eddies, ecosystem processes, and biodiversity are still not elucidated in the NACES MPA, this study created a framework to help identify other candidate MPAs in these systems. Multi-species tracking data and high-resolution oceanographic models were instrumental in achieving this and will be vital to establishing MPAs in international waters in the future.