Study warns sharp decline in Antarctic krill by 2100

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 Foto: Centro IDEALFoto: Centro IDEAL

By Sebastián Silva Alcaíno
A study carried out by scientists from various Chilean institutions and published in the international scientific journal Progress in Oceanography has revealed that by the year 2100 there will be a decline in the biomass of Antarctic krill. This crustacean is considered key in the food web of the white continent. It is a situation that could lead to the displacement of numerous species that depend on krill, including diverse whales, penguins, seals, and fish.
"Krill is a key species in the Antarctic ecosystem because many organisms depend on it and are responsible for efficiently transferring energy from lower to higher trophic levels," says Dr. Andrea Piñones, an oceanographer at the Universidad Austral de Chile (UACh) and co-author of the article. 
Antarctic krill gather in large schools. The study, which involved scientists from the Universidad Austral de Chile and the Universidad de Concepción, determined through predictive models the effect of different environmental and anthropogenic factors on krill (Euphasia superba), which measures between just 6 and 7 centimeters long.
The researchers used a trophic model called Ecopath. With it they made three environmental climate projections under parameters such as sea ice extent and chlorophyll concentration, in addition to analyzing anthropogenic variables related to the krill fishery.  The area sampled included the western part of the Antarctic Peninsula, from Alexander Island to eastern Elephant Island.
The study reflected the importance of environmental variables in the development of this organism, with special emphasis on chlorophyll-a, a photosynthetic pigment produced by phytoplankton, food for krill. The amount of this element strongly influenced the variability of the Antarctic food web in the future, generating changes toward the end of the century. The research also detected the increase of other zooplanktonic organisms, such as salps.
The decline in krill biomass will also mean a displacement of species that depend on it, such as penguins and crabeater seals. Photo: Ricardo Giesecke.The decline in krill biomass will also mean a displacement of species that depend on it, such as penguins and crabeater seals. Photo: Ricardo Giesecke.
Climate change is one of the main factors impacting the distribution and life cycles of Antarctic krill: "Biomass will be negatively affected by a change in food distribution and/or changes in sea ice distribution, mainly sea ice reduction. During early life stages, factors such as water temperature at depth and changes in pCO2 levels (acidification) may be relevant, while adult organisms may be subject to pressure from fisheries or consumption by predators that depend on them,” Piñones said in an interview.
Regarding the displacement of species that would take place as a result of this change, Piñones adds: "One of the implications could be a local restructuring of the trophic web of coastal areas such as Antarctic fjords and bays. If krill disappears from a certain region, the species that depend on it are forced to change their diet and/or to move and follow the krill wherever it is."
The results of the predictive model determined a low influence of the fishery on the decrease of the biomass of this organism. However, experts say that more studies are needed to determine more precisely how this variable impacts krill biomass.
Regarding how these results may be reflected in whales, Dr. Piñones affirms: "Since the moratorium on commercial whaling, they have been doing quite well, they have been recovering in numbers. However, if your main food is krill and this is reduced, as a consequence you will be affected. But I cannot say specifically at what level and what the consequences would be. Perhaps a bioenergetics model for whales could help to elucidate this question."
The conclusions of this research suggest a sharp decline in Antarctic krill biomass between now and the end of the century under all climate scenarios and independent of fishing pressure. "The next steps will be to corroborate the results obtained in the field and improve the model to better represent the life cycle of the species and the distribution of fisheries, in order to obtain more representative projections," said Dr. Giovanni Testa, an oceanographer at Universidad de Concepcion and leader of the study.

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