New ice-free areas, an opportunity for colonizers? An striking from Potter Cove.

SAHADE, RICARDO; LAGGER, CRISTIAN

Madralin

Workshop; IPY-ClicOPEN Workshop 2009.; 2009

The retraction process that are experiencing the majority of the glaciers in the Antactic Peninsula besides affecting coastal ecosystems are also leaving new habitats available for coloniozers. In Potter Cove the retreat of the Fourcade glacier had left free an important area in the NE coast of the Cove including a couple of new islands. The bigger island was sampled during the last summer by phototransects take up to 25 m depth where the island wall encounter the bottom. Surprisingly a really dense macrofaunal community dominated by ascidians, especially by the species Molgula pedunculata and Cnemidocarpa verrucosa, was found. Although, the diversity was not as high as in the surrounding among the highest registered, even compared with the inner cove communities before the registered shifts when these species were dominant. Then the queston is, did these communities colonize and were established after the ice was retired or they were present and developing under the ice cup? Although the results analyses are not yet finishep we can provide some insights to discuss. In first term the size and densities of ascidians suggest at least several years of development, unfortunately little is known on growth rates (although can be considered high for Antarctic species) and age of ascidians. Besides that other groups as sponges, wich are supposed to grow slowly, are also present and the communities start abruptly at around 7 m depth. These observations suggest that could be possible that this community was developing under the ice. On the other hand could be possible the existence of a pocket in the glacier front, then there would be necessary the input of organic matter to support this animal abundance. If the community is new, wich is the population source?, since this species were the most affected by the observed shifts in the cove and then we will have to revise our concept of growth rates of Antarctic organisms including ascidians and sponges. And if they were already there could be this, an extended feature or just an exceptional case in an ice pocket?