Melting glaciers are snuffing out Antarctic seafloor life

Climate change has been intense on the Antarctic Peninsula. Over the past 50 years temperatures on the Peninsula, the northernmost part of the Antarctic mainland that juts toward the southern tip of South America, have risen almost five times faster than the global average. Ice shelves are collapsing and glaciers are rapidly retreating, and scientists predict these changes will have consequences for the surrounding ocean.

So far, the scant research investigating those predictions has mainly focused on creatures like krill and penguins that swim freely in the water column. But most Antarctic marine species are bottom-dwelling organisms. Now, a long-term study suggests that the indirect effects of climate change could cause seafloor biodiversity to dwindle.

In 1994, 1998, and 2010, divers photographed the sea floor in Potter Cove, a fjord in the South Shetland Islands off the western Antarctic Peninsula. At each of three locations – near the head of the cove, near the mouth of the cove, and at an intermediate spot – they took photos at depths of 15, 20, 25, and 30 meters.

Researchers then analyzed these photographs, counting the number of organisms at least 1 centimeter in size and estimating the amount of the sea floor covered by different species. They compared the communities of bottom-dwelling organisms at different locations and different time points. They also looked at the relationships between these biological data and sedimentation rates, water temperatures, and other physical and chemical measurements collected in different parts of the cove.

The seafloor community in Potter Cove has undergone major shifts in response to climate change, but temperature isn’t the major factor driving these patterns. Instead, the cause is increased sedimentation due to runoff from melting glaciers, the researchers reported last week in Science Advances.

At the head of the cove, where meltwater from the Fourcade Glacier pours into the ocean, the amount of sediment in the water has increased sharply over the past 20 years along with the glacier’s retreat. Some organisms – notably tall species of ascidians, or sea squirts – cannot tolerate the murkier water and have disappeared from these parts of the cove. There, the seafloor community has switched from one dominated by filter-feeding ascidians to a more mixed but species-poor assemblage.

In the past, Antarctic fjords like Potter Cove have experienced fairly high sedimentation rates. But above certain thresholds, the study suggests, bottom-dwelling communities may suddenly shift to a less diverse sort of ecosystem. And it’s not clear whether or not such changes will be reversible, the researchers say.

That’s particularly concerning because these fjords tend to host a large number of bottom-dwelling species. So as glaciers continue to retreat in Antarctica, increased sedimentation could pose a major threat to these hotspots of Antarctic diversity. “The loss of important species is changing the coastal ecosystems and their highly productive food webs,” says study team member Doris Abele, a biologist at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, “and we still can’t predict the long-term consequences.” – Sarah DeWeerdt | November 17, 2015

Source: Sahade R. et al. “Climate change and glacier retreat drive shifts in an Antarctic benthic ecosystem.” Science Advances DOI: 10.1126/sciadv.1500050

Header image: Seafloor community in Potter Cove. Credit: Alfred Wegener Institute / Christian Lagger (CONICET).

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