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Sediment from Melting Glaciers Changes Antarctic Sea Floor Communities

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Before sediment runoff increased at the Antarctic Peninsula, researchers say the sea floor there was inhabited by a more diverse range of species. | Ricardo Sahade

The prevailing image of Antarctic seabed life is that of stability, but increased sediment runoff caused by glacier retreat may be driving a major shift in the types of seabed organisms dwelling in the Antarctic Peninsula, a long-term study suggests.

The research appears in the 13 November issue of the journal Science Advances.

The Antarctic Peninsula is one of three places on Earth that has experienced the most intense warming in the last 50 years, causing the largest ice shelf collapses ever observed and the retreat of 87% of its glaciers. Researchers have predicted responses to this warming across the food chain, from krill to phytoplankton, but the major effects of climate change on the abundant and diverse communities on the Antarctic sea floor to date have been restricted to just a few species.

These sea floor or benthic communities play a fundamental role in the coastal food webs that sustain penguins, seals, and whale populations in the area, said lead author Ricardo Sahade, a professor at the National University of Córdoba in Córdoba, Argentina.

"It was amazing in our first dives in Potter Cove [South Shetland Islands, Antarctica] to see these wonderful and diverse [benthic] communities, where giant ascidians, accompanied by sponges, anemones, sea-pens, starfishes, and sea urchins were so abundant in those muddy bottoms," said Sahade.

By performing a series of underwater photographic surveys of benthic ecosystems in the Antarctic in 1994, 1998, and 2010, the researchers showed that the community structure first detailed in the 1990s has since shifted.

The communities now contain less species diversity and abundance, and have become dominated by suspension feeders, which get nutrients by straining them from water, the researchers found. Species that stay in place, such as sea squirts, are becoming less frequent while more mobile species are on the rise.

The scientists weren't sure at first what caused this shift on the sea floor, but by analyzing the physiological responses of certain species to sediment changes, and reconstructing the sedimentation history of Potter Cove, they were able to link the shift to increased sediment runoff.

Sahade and his colleagues suggest that glacier melt may have greatly increased sediment runoff in the area, making portions of the seabed inhospitable to organisms unable to cope with the increased sedimentation.

As glacier retreat continues, sedimentation is likely to be an important factor in coastal ecosystem dynamics. Moreover, conditions at Potter Cove could extend along the Western Antarctic Peninsula in the near future, representing a major threat for these hot spots of Antarctic diversity, the scientists say.

 

[Credit for associated teaser image: Ricardo Sahade]