Consideration of Midwater Ecosystems is Required to Fully Evaluate the Environmental Risks of Deep-Sea Mining

Despite rapidly growing interest in deep seabed mineral exploitation, environmental research and management have focused on potential impacts to benthic environments and have paid little attention to pelagic ecosystems. Yet pelagic ecosystems have established ecological and societal importance. Seafloor mining activities will generate sediment plumes and noise in the benthic boundary layer and higher in the water column that may have extensive ecological effects in deep midwaters, depths from ~200m to the seafloor. These ecosystems represent more than 90% of the livable volume on our planet, contain a fish biomass 100 times greater than the global annual fish catch, connect shallow-living ecosystems to deeper ones including the benthos, and play key roles in carbon export, nutrient regeneration, and in the provisioning of harvestable fish stocks. These deep midwater ecosystem services as well as biodiversity could be negatively affected by mining. We will examine the potential effects of deep seabed mining on midwater ecosystems and provide specific recommendations on how ecosystem risks could be more comprehensively and effectively evaluated.