New Ice-Free Areas in Antarctic shallow-waters: an Opportunity for Sponge Colonization?

LAGGER, CRISTIAN; CÁRDENAS, CÉSAR

Galway

Congreso; 10th World Sponge Conference; 2017

The Antarctic Peninsula has warmed significantly over recent decades, being considered among the fastest warming regions on Earth. This warming has profound influences on the cryosphere including ice shelf collapses and a decrease in extent and seasonality of sea-ice. Furthermore, the majority of glaciers have retreated during the last 60 years. Particularly, the Fourcade Glacier surrounding Potter Cove (South Shetland Island, Antarctica) shows an accelerated retreat affecting the hydrographical characteristics of the cove; hence, driving significant changes in the established benthic communities. In addition, the glacier retreat has also uncovered a new rocky island representing anexcellent opportunity to study colonization and succession processes in Antarctic ecosystems. We sampled the new island by photo-transects taken up to 30 m depth by SCUBA diving, six years after that it was freed of ice (March 2010). Here, we report a particular benthic assemblage characterized by high species richness, diversity and structural complexity with a well-developed three-dimensional structure, dominated by filter feeders at all depths. Sponges were the second most important group in terms of abundance in the new island with a mean of 3.03 ± 0.32 percent cover. Total abundance of sponges decreased markedly across the bathymetric gradient, with the lowest cover (0.9 ± 0.31%) recorded at 30 m depth. The sponge Haliclona sp. 2 was the most abundant taxa, representing between 25 and 70% of total sponge coverage. We registered large individuals reaching more than 50 cm in length (sponges of up to 0.02m3). Considering if individuals have settled and grown for only six years, it will represent a high growth rate, higher than previously reported for demosponges in Polar Regions, hence confirming recent findings reported from East Antarctica and challenging the widely held assumption of low velocity processes in Antarctic benthos. However, it also opens the question of whether these sponges could have been present under the glacier in ice refuges and now have been exposed to open sea conditions. Sedimentation will increase under the current scenario of glacier retreat, affecting filterfeeders and other sessile benthic organisms such as sponges, which may be vulnerable. For this reason, sponges may constitute suitable indicators of climate induced perturbations along the Antarctic Peninsula. On the other hand, the opening of new areas available for sponge colonization that could take place at previously unexpectedvelocity, shows the need for a better understanding on the interactions between physical and biological variables and how they affect sponge assemblages