Risk maps for Antarctic krill under projected Southern Ocean acidification

Abstract

Marine ecosystems of the Southern Ocean are particularly vulnerable to ocean acidification¹. Antarctic krill (Euphausia superba; hereafter krill) is the key pelagic species of the region and its largest fishery resource². There is therefore concern about the combined effects of climate change, ocean acidification and an expanding fishery on krill and ultimately, their dependent predators—whales, seals and penguins^3,4. However, little is known about the sensitivity of krill to ocean acidification. Juvenile and adult krill are already exposed to variable seawater carbonate chemistry because they occupy a range of habitats and migrate both vertically and horizontally on a daily and seasonal basis⁵. Moreover, krill eggs sink from the surface to hatch at 700–1,000 m (ref. 6), where the carbon dioxide partial pressure ($p_{{\text{CO}}_{\text{2}}}$) in sea water is already greater than it is in the atmosphere⁷. Krill eggs sink passively and so cannot avoid these conditions. Here we describe the sensitivity of krill egg hatch rates to increased CO₂, and present a circumpolar risk map of krill hatching success under projected $p_{{\text{CO}}_{\text{2}}}$ levels. We find that important krill habitats of the Weddell Sea and the Haakon VII Sea to the east are likely to become high-risk areas for krill recruitment within a century. Furthermore, unless CO₂ emissions are mitigated, the Southern Ocean krill population could collapse by 2300 with dire consequences for the entire ecosystem.