Potential climate change effects on the habitat of Antarctic krill

Antarctic krill is an obligate cold water species, an increasingly important fishery resource and a major prey item for many fish, birds and mammals in the Southern Ocean. The fishery and the summer foraging sites of many of these predators are concentrated between 0° and 90°W. Parts of this sector have experienced recent localised sea surface warming of up to 0.2°C     per decade, and projections suggest that further widespread warming of 0.27° to 1.08°C will occur by the late 21st century. We used a statistical model linking Antarctic krill growth to temperature and chlorophyll concentration to assess the influence of projected warming on Antarctic krill habitat quality. The results divide the sector into two zones: A band around the Antarctic Circumpolar Current in which habitat quality is particularly vulnerable to warming; and a southern area which is relatively insensitive. Our analysis suggests that the direct effects of warming could reduce the area of growth habitat by up to 20%. The reduction in growth habitat within the range of predators, such as Antarctic fur seals, foraging from breeding sites on South Georgia could be up to 55%, and the habitat’s ability to support Antarctic krill biomass production within this range could be reduced by up to 68%. Sensitivity analysis suggests that a 50% change in summer chlorophyll concentration could have a more significant effect on Antarctic krill habitat than the direct effects of warming. A reduction in primary production could lead to further habitat degradation but even a 50% increase in chlorophyll would not completely negate the degradation of habitat available to predators. While there is considerable uncertainty in these projections, they provide strong and specific evidence that climate change poses a threat to Antarctic krill growth habitat and consequently to Southern Ocean biodiversity and ecosystem services.