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PUBLISHED ONLINE: 7 JULY 2013 | DOI: http://www.nature.com/doifinder/10.1038/nclimate1937
Web End =10.1038/NCLIMATE1937
Risk maps for Antarctic krill under projected
Southern Ocean acidication
S. Kawaguchi1,2*, A. Ishida3,4, R. King1, B. Raymond1,2, N. Waller1, A. Constable1,2, S. Nicol5,M. Wakita4,6 and A. Ishimatsu7
Marine ecosystems of the Southern Ocean are particularly vulnerable to ocean acidication1. Antarctic krill (Euphausia superba; hereafter krill) is the key pelagic species of the region and its largest shery resource2. There is therefore concern about the combined effects of climate change, ocean acidication and an expanding shery on krill and ultimately, their dependent predatorswhales, seals and penguins3,4.
However, little is known about the sensitivity of krill to ocean acidication. 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 7001,000 m (ref. 6), where the carbon dioxide partial pressure (pCO2) 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 pCO2 levels. We nd 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.
To assess the sensitivity of krill embryonic development to ocean acidification, we experimentally exposed krill eggs to elevated seawater CO2 levels (see Methods). Hatch rates were similar for krill eggs spawned at 380 and 1,000 atm pCO2, but were significantly lower in the 1,250 atm pCO2 treatment. Hatch rates were roughly 20% of control levels at 1,500 atm pCO2 and almost no hatching was observed at 1,750 and 2,000 atm pCO2 (Fig. 1). Increased levels of CO2 in the sea water also delayed embryonic development. At 8 days, embryos that had not hatched but were still alive had developed to mid limb-bud stage in the 1,250 and 1,500 atm pCO2 exposures but...