New ice-free areas in Potter Cove: Another opportunity for the populations of the ascidian Cnemidocarpa verrucosa?

LAGGER, CRISTIAN; ZAMBONI, NADIA; TARANTELLI, SOLEDAD; ACOSTA, SOLEDAD; DEMARCHI, MILAGROS; RIMONDINO, CLARA; SERVETTO, NATALIA; TATIÁN, MARCOS; TORRE, LUCIANA; WIERNES, PAULA; SAHADE, RICARDO

Congreso; SCAR XXXI & Open Science Conference; 2010

The benthic communities at Potter Cove showed important shifts in three years (1995 to 1998). These shifts were especially marked in soft-bottoms, where ascidians almost disappeared at 20 m depth and showed a great reduction at 30 m. One of the most affected ascidian species was Cnemidocarpa verrucosa, one of the dominant species both in density and percentage cover. One decade later (2009/2010), the photo transects were repeated at the same stations and depths. The results showed that density of C. verrucosa decreased, suggesting that the population reduction trend was maintained in the inner cove. These shifts could be due to the increase in sediment load and ice impact. However, a different situation was observed in the newly ice-free areas. The retraction of the Fourcade Glacier left an important area free of ice at the cove which includes a new island. Last summer, this island was sampled by photo transects. Surprisingly, a dense macrofaunal community dominated by C. verrucosa was found, even at shallow depths. The density and abundance values obtained are the highest recorded for this cove. The hard substrate, a vertical wall arrangement and fewer iceberg impacts, compared to horizontal substrates, could create a favourable environment for this relatively new population giving it an advantage in feeding activities. The question now is if abundance at different depths will decrease in the future, following what happened in the soft-bottoms, or if no change will occur, making this island a source (relict place) for the colonization of new ice-free areas.