Krill in Peril

The Southern Ocean is home the greatest amount of sea ice and pack ice.  Frozen sea water covers the ocean and is an intricate part of the life histories of many antarctic species.  Antarctic krill (Euphausia superba) rely heavily on sea ice to complete their life cycles (Daly 1990).   Krill density abundance around ice edges and the under-surfaces of pack ice clearly indicates a large habitat preference for this species.  This is especially true for krill larvae and krill in their final developmental stage (Furcilia) in which time the juveniles reach maturity.  Their preference for sea ice is associated with the physical refuge the ice provides as well as the high levels of productivity and available food found on the underside of sea ice.  Ice algae is found on the underside of seasonal ice packs and are the main component to the the diet of E. superba.  Also, stomach content analysis of krill indicate their consumption of detritus (organic material) and zooplankton such as tintinnids and dinoflaggelates.  This preference is especially noted in juvenile krill who have not reached maturity exibited the schooling behavior that enables this species to live in open ocean waters.  Sea ice provides the optimal environmental for the krill, who are able to seek refuge under its protective layer, away from from the natural predators and nutrient poor limitations found in the open ocean.

Alae growing on the underside of sea ice
Photograph source: Chris Fritsen, United States Antarctic Program

Impacts of Climate Change


Therefore the extent of sea ice plays a deciding factor in the abundance and persistence of Antarctic Krill.   The Intergovernmental Panel on Climate Change  (IPCC) produces reports on the extent of climate change associated with the increases concentrations of greenhouse gases associated with the burning of fossil fuels.  Although there is uncertainty and variation as to how much temperature has risen in the southern ocean, most surveys and reports show a definite increase in water temperatures associated with the increase global surface temperatures brought upon by climate change (IPCC 2007).   Some areas of the southern ocean have experienced a warming of 2.5 degrees Celsius over the past 50 years, an temeperature rise five times faster than the mean global rate (UNEP 2006).   Not only will climate change reduce the extent of  ice, it will increase the seasonal variability of ice shelves and sea ice.

The amount of sea ice loss in the Antarctic is difficult to determine.  On the opposite pole, the Arctic has shown severe losses in annual sea ice and ice shelf cover (Douglas 2010).  In this area seasonal variations in ice cover have increased dramatically and in certain areas, entire months have gone without the emergence of historical onsets of ice influx.  This has resulted in the public and even scientific community to doubt the extent current and future of climate change and global warming in the ataractic and Southern Ocean.  This misconception may exist for two reasons.  First, the analysis of increased temperatures and its effect on Antarctic sea ice has been constrained by limited observation and research (Lie and Curry 2010).  Also, climate change in the Antarctic is less apparent because of the extent of the enhanced hydrological cycle.   Increased temperatures in the northern portion of the Southern Ocean (mid latitude) has resulted in increased evaporation and moisture content in the troposphere.  This moisture is carried south to high latitudes due to the physical atmospheric circulation known as the Ferrell Cell.   This results in the increased precipitation and freshwater input in the Antarctic.   This lowers the surface ocean salinity and water density.  Fresher water means a higher freezing point.  The reduced density of ocean water reduces the density driven current found in polar regions that upwaells energy and helps sustain normal sea ice melting.  Together, two properties of the Antarctic waters that assist melting of sea ice -high water salinity and density- are being dampened due to the increased sea surface temperature (SST) and evaporation at lower latitudes.

Human Impacts


The Antarctic Krill fishery of the Southern Ocean is the largest by tonnage when compared to the several fish and other marine species harvested there (Nicol et al. 2011).  The most heavily harvested areas are the waters of the Antarctic Peninsula, The south Orkney Islands and South Georgia.  In the 2009-2010 season, the Conservation of Antarctic Marine Living Resources (CCAMLR) reported that 211,180 tonnes of krill were harvested.   The increased reliance on krill as fish feed for aquaculture and other fish industries has increased dramatically as the small crustacean offers a nutrient rich and efficient food source (Schiermeier 2010).  Below is the annual global catches of Antarctic krill as reported by CCAMLR.  As displayed, there has been a large decline in human harvesting.  However, the larger and more ominous threat is climate change, therefore this website will focus solely on the impacts of warming in the Southern Ocean.  Lastly, human are the number one driver of carbon emissions and global warming, therefore the future of krill will be determine by the indirect impacts of anthropogenic climate change.

Original Figure- Data provided by the Commission for the Conservation of Antarctic Marine Living Resources
CCAMLR. 2012. Statistical Bulletin, Vol. 24 (Database Version)