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L'Antàrtida, molt més que gel J.M. Gasol. Xarxes
tròfiques planctòniques: per què són diferents als mars de l’Antàrtida. One of the most amazing characteristics of the Antarctica is the presence of large numbers of vertebrates, birds and mammals. These animals are the top vertexes of food webs based uniquely in the marine environment. We explain here the reasons why the Southern oceans provide so much food usable by higher trophic levels. The cold waters of Antarctica are full with nutrients and thus allow high levels of primary production. The type of algae that dominate are relatively large diatoms and flagellates, which serve as a direct food source to krill, which, in a way, shunt fixed carbon directly from the producers to a form, krill, which is directly usable by vertebrates. Other factors contribute also to the high transfer efficiency of the Antarctic food webs: the relatively depressed bacterial activity at low temperatures, but also the dependence of krill and algae on sea ice for winter survival. Recent reports of global change in Antarctica point to a relationship between increasing temperatures, sea ice extent, and a shift in the size distribution of algae towards forms that are more edible by salps than by krill. A change towards food webs controlled by krills would have high impacts on the Antarctic bird and mammal populations as well as on biogeochemical cycling. |
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