Seawater carbonate chemistry and hatch rates of Antarctic krill@en

Marine ecosystems of the Southern Ocean are particularly vulnerable to ocean acidification. Antarctic krill (Euphausia superba; hereafter krill) is the key pelagic species of the region and its largest fishery resource. 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. 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 basis. Moreover, krill eggs sink from the surface to hatch at 700-1,000 m, where the carbon dioxide partial pressure (pCO2) in sea water is already greater than it is in the atmosphere. 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 pCO2 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.南大洋海洋生态系统对海洋酸化（ocean acidification）尤为脆弱。南极磷虾（Euphausia superba，后文简称磷虾）是该海域关键的远洋浮游物种，亦是当地规模最大的渔业资源。因此，学界担忧气候变化、海洋酸化与持续扩张的捕捞业三者的共同作用，将对磷虾种群乃至其依赖的捕食者——鲸类、海豹与企鹅——造成不利影响。然而，目前学界对磷虾耐受海洋酸化的敏感性仍知之甚少。幼体与成体磷虾栖息于多样生境，并会开展每日及季节性的垂直与水平洄游，因此早已处于波动的海水碳酸盐化学环境中。此外，磷虾卵会从表层海水下沉，在700至1000米水深处孵化，该深度的海水二氧化碳分压（pCO₂）已高于大气中的水平。磷虾卵依靠被动下沉，因此无法规避此类环境。本研究探讨了磷虾卵孵化率对二氧化碳浓度升高的敏感性，并基于预估的pCO₂水平，绘制了环南极海域磷虾孵化成功率风险分布图。研究发现，威德尔海与东侧的哈康七世海作为磷虾重要栖息海域，将在未来百年内逐步成为磷虾种群补充的高风险区域。此外，若不采取措施减缓二氧化碳排放，到2300年南大洋磷虾种群或将濒临崩溃，对整个海洋生态系统造成灾难性后果。