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Antarctic krill and climate change in the Western Antarctic Peninsula (WAP). Antarctic krill are a key species in Antarctic food webs. They feed on diatoms, microzooplankton, and copepods and are the major food source for many top predators including baleen whales, seals, and sea birds including penguins.
However, krill in the WAP region have declined two-fold since the mid-1970s due to profound changes along the WAP in the past decades. The west coast of the northern WAP is changing from a cold, dry polar climate to a warmer, humid subantarctic climate because of a 6°C increase in mid-winter surface atmospheric temperatures (> than 5x the global average) in the past 50 years. As a result, sea ice is declining. At the same time. there have been changes in the biomass and composition of krill food source, the microscopic plants in the ocean called phytoplankton. Reproductive output and recruitment success of Antarctic krill in the WAP region has been linked to sea ice extent and duration, and recruitment success is the major driving factor for krill population size. There remains considerable uncertainties regarding krill growth and the effects of environmental factors on growth rates. The reduction in sea ice as well as the biomass and size of phytoplankton in the region has been reflected not only in krill declines, but also in the 90% decline of Adélie penguins in the past 30 years in the northern WAP.
Reproductive output and recruitment success of Antarctic krill in the WAP region has been linked to sea ice extent and duration, and recruitment success is the major driving factor for krill population size. There remains considerable uncertainties regarding krill growth and the effects of environmental factors on growth rates.
Ocean acidification and effects on organisms. In addition to rapid warming in the WAP region, it is predicted that by the end of this century the Southern Ocean will be the first region to be affected by seawater chemistry changes associated with enhanced atmospheric carbon dioxide (CO2). Human activities such as burning of fossil fuels, deforestation, and cement production have driven the rapid 40% increase in atmospheric CO2, from preindustrial levels of 280 ppmv (parts per million volume) to current levels of nearly 400 ppmv. Nearly one third of emitted anthropogenic CO2 is absorbed by the oceans, resulting in increased acidity of seawater. This is known as ocean acidification. These changes are expected to cause adverse effects, propagating from individual species of both calcifying and non-calcifying marine organisms to entire ecosystems.
Ocean acidification can impact marine organisms by decreasing carbonate saturation which reduces calcification rates and can reduce or negatively impact the growth and development of early life stages. Additionally, ocean acidification has a wide-ranging potential for impacting the physiology and metabolism of marine organisms. Sufficiently elevated CO2 concentrations can alter internal acid-base balance, compromising homeostatic regulation and disrupting internal systems ranging from oxygen transport to ion balance. These processes are extremely important because even subtle changes can have large impacts on the success of individual organisms and populations.