Newly ice free areas in Antarctica and its consequences for coastal benthic ecosystems

Underwater pictures taken on the wall of the new island at Potter Cove. Both pictures were taken between 10 and 15 m depth where a high abundances of filters feeders such as ascidians and sponges were found. Note the aluminum ruler (10 cm long) that was attached to the underwater camera and was used to quantify the sampled area.

By Cristian Lagger and Ricardo Sahade

The Antarctic Peninsula and large parts of West Antarctica have warmed significantly over recent decades and are considered among the fastest warming regions on Earth. This warming have lead to an increasing loss of ice, including ice-shelf collapses, a decrease in the extent and seasonality of sea-ice and the retreat of the majority of tidewater glaciers in these regions (Cook et al. 2014). The 25 de Mayo/King George Island, one of the South Shetland Islands where Potter Cove is located, is not an exception (Rückamp et al. 2011). The Fourcade Glacier surrounding Potter Cove shows an accelerated retreat, affecting the hydrographical characteristics of the cove and driving significant changes in established benthic communities. We recently reported a sudden shift in benthic communities structure related to increased sedimentation rates driven by this glacier retreat at Potter Cove (Sahade et al. 2015). This highlighted the potential role of sedimentation in driving major changes in coastal communities, and also suggested the possibility of thresholds in environmental factors. This could be important in communities dynamics since gradual changes in environmental variables could not drive responses until the threshold is surpassed and trigger major shifts that could also be difficult to reverse.

On the other hand, the opening up of new areas for benthic colonisation is another important effect of the loss of ice. Particularly, in Potter Cove, the remarkable retreat of several hundred metres of Fourcade Glacier uncovered a new rocky island in the inner part of the cove (Rückamp et al. 2011). This new island offers an excellent opportunity to study colonisation and primary succession in polar coastal areas that have largely been considered as slow processes. In a recent paper published in Ecography, we report an unexpected benthic assemblage in the new island characterised by high species richness, diversity and structural complexity with a well-developed three-dimensional structure and epibiotic relationships. Filter feeders comprised the largest trophic group at all depths, mainly ascidians, sponges and bryozoans. Recorded densities were an order of magnitude higher than previous Antarctic reports on early colonisation.

A real picture of the new island in front of Fourcade glacier and a schematic drawing of the underwater topography. Pictures of different organisms (macroalgae, ascidians, sponges, sea-stars) found on the island are shown in the circles.

It is thus still not clear if the assemblages observed are the result of extraordinary fast colonisation, or if these complex assemblages could have been present under the glacier in ice-free refuges that are now exposed to open-sea conditions. The first scenario of a rapid response would be important for enabling the conservation and survival of these threatened coastal benthic ecosystems along the Antarctic Peninsula, especially inside fjords that are also important biodiversity hotspots (Grange and Smith 2013). Also, this possibility challenges the extended idea of a slow and continuous recruitment in Antarctica. But also suggest that the negative feedback to climatic change in newly ice free areas could be more important than previously thought (Peck et al. 2010). In contrast, the second scenario would be the exposure of these previously protected assemblages to new unfavourable conditions that could drive to its collapse as it was already observed in assemblages exposed to high sedimentation (Sahade et al. 2015).

This work offers new insights on colonization of newly ice-free areas in Antarctica, which species respond first and how a polar ecosystem can responds to climate change. This work is based on more than 20 years of multidisciplinary research at the Potter Cove coastal ecosystem that established basis against which to compare current results and evaluate temporal and dynamic processes driven by the Antarctic Peninsula warming. Considering the massive glacier retreat experienced by the Antarctic Peninsula, this new paper in Ecography will provide a valuable basis to improve the current understanding and prediction capabilities of processes that would extend along Antarctica.

Reference

Cook, A. J. et al. 2014. A new Antarctic Peninsula glacier basin inventory and observed area changes since the 1940s. – Antarctic Sci. 26: 614–624.

Grange, L. J. and Smith, C. R. 2013. Megafaunal Communities in Rapidly Warming Fjords along the West Antarctic Peninsula: Hotspots of Abundance and Beta Diversity. – PLoS One 8: doi:10.1371/journal.pone.0077917.

Peck, L. S. et al. 2010. Negative feedback in the cold: ice retreat produces new
carbon sinks in Antarctica. – Glob. Change Biol. 16: 2614–2623.

Rückamp, M. et al. 2011. Observed glacial changes on the King George Island ice cap, Antarctica, in the last decade. – Global and Planet. Change 79: 99–109.

Sahade, R. et al. 2015. Climate change and glacier retreat drive shifts in an Antarctic benthic ecosystem. – Sci. Adv. 1(10): e1500050.

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