Benthic Antarctic Ecosystems and their Potencial Response to Global Warming: first insights.

SAHADE, RICARDO; DEMARCHI, MILAGROS; LAGGER, CRISTIAN; MERCURI, GUILLERMO; MOMO, FERNANDO; SERVETTO, NATALIA; TARANTELLI, SOLEDAD; TATIÁN, MARCOS; TORRE, LUCIANA

Madralin

Workshop; IPY-ClicOPEN Workshop 2009.; 2009

Shallow benthic communities in Antarctica have been considered to possess a high stability, especially below high ice impact zones, since environmental factors are constant or highly predictable, resembling those of deep-sea habitats. However, the benthic communities at Potter Cove exhibited important shifts in just three years. Ascidians, that were the dominant taxa almost disappeared at 20 m depth and at 30 m showed a great retraction together with sponges. The most affected ascidian species was Molgula pedunculata, wich was the dominant species both in desities and percentage cover. While other ascidian species like Ascidia challengeri and Corella eumyota incremented their densities but decreased their percentage cover suggesting a decrease in the individuals sizes. On the other hand, the bivalve Laternula elliptica and the pennatulid Malacobelemnon daytoni that were dominant at 15 m depth became dominants at 20 m extending their dominance to deeper waters wich the ascidians retraction. While other non filter-feeders as gastropods, asteroids and ophiuroids increased their abundances as well. Although these processes could be related to natural local extinctions, recruitment events or interannual-interdecadal population variations, the increase of sediment load in the water column and ice impact at shallow depth caused by glacier retraction could be considered the best candidates to explain the observed shifts. It was striking the velocity of the change, wich suggest that this could be a system that is not gradually responding to external factors but shifting once a threshold limit is reached, state that might be difficult to reverse wich could represent alternative stable states. These results suggest that the main effects of global warming in Antarctic benthic coastal ecosystems could be manly driven by the increase of sedimentation and ice action during these first steps.