Benthic Antarctic Ecosystems and Potential Response to Global Warming: first insights

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

Madralin (Polonia)

Workshop; Response of marine and terrestrial biota along the Western Antarcic Peninsula to climate change and the global context of the observed change; 2009

Polish Polar Committee, German Science Foundation

Shallow benthic communities in Antarctica have been considered to possess a highstability, especially below high ice impact zones, since environmental factors areconstant or highly predictable, resembling those of deep-sea habitats. However, thebenthic 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 mshowed a great retraction together with sponges. The most affected ascidian species wasMolgula pedunculata, wich was the dominant species both in desities and percentagecover. While other ascidian species like Ascidia challengeri and Corella eumyotaincremented their densities but decreased their percentage cover suggesting a decreasein the individuals sizes. On the other hand, the bivalve Laternula elliptica and thepennatulid Malacobelemnon daytoni that were dominant at 15 m depth becamedominants at 20 m extending their dominance to deeper waters wich the ascidiansretraction. While other non filter-feeders as gastropods, asteroids and ophiuroidsincreased their abundances as well. Although these processes could be related to naturallocal extinctions, recruitment events or interannual-interdecadal population variations,the increase of sediment load in the water column and ice impact at shallow depthcaused by glacier retraction could be considered the best candidates to explain theobserved shifts. It was striking the velocity of the change, wich suggest that this couldbe a system that is not gradually responding to external factors but shifting once athreshold limit is reached, state that might be difficult to reverse wich could representalternative stable states. These results suggest that the main effects of global warming inAntarctic benthic coastal ecosystems could be manly driven by the increase ofsedimentation and ice action during these first steps.