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Scientists say melting glaciers are now threatening Antarctic ocean life

Antarctic benthic communities: A unique feature of these communities is that even in soft-bottoms and under high sedimentation, they can be dominated by epibenthic filter-feeders. This picture is before they showed a sudden shift caused by increased sedimentation. (Image credit: Ricardo Sahade)

Much of the scientific work on the fascinating and unique organisms occupying the seas around Antarctica has focused on concerns that rising temperatures will upend these communities. But that’s not the only aspect of climate change we should be worrying about, scientists say. New research suggests that melting glaciers, which produce runoff water that carries extra sediment down into the ocean in the form of silt or clay particles, could be causing big changes in some Antarctic communities.

So-called “benthic” zones, or the areas at the bottom of the ocean, are some of the most diverse and productive ecosystems in Antarctica, said Craig Smith, a professor of oceanography at the University of Hawaii. These areas tend to be dominated by suspension feeders like sea squirts, which are animals that eat tiny materials suspended in the water (such as plankton).

But if too much sediment gets into the water, these creatures have a hard time filtering out their food and can start to die off. And it appears that this is what’s happening in at least one community off the coast of the Antarctic Peninsula.

[Scientists confirm their fears about West Antarctica — that it’s inherently unstable]

A new study, published on Friday in the journal Science Advances, took a look at an ocean bottom ecosystem in the South Shetland Islands, which are located just north of the Antarctic Peninsula. The peninsula is known for experiencing some of the most rapid regional warming in the world, and its high glacier melt rate is a major subject of a concern for scientists. 

The study’s authors, led by Ricardo Sahade, a researcher at the Institute of Diversity and Animal Ecology at the National University of Cordoba, conducted photographic surveys of three sites in the area. The first, known as the “inner station,” had a high rate of sediment carried down by glacial meltwater. The second site, or “middle station,” was strongly affected by sedimentation in deeper areas, but less so in shallower waters. And the third site, or “outer station,” was not strongly affected by sedimentation.

By comparing the types of animals found in these three sites over time, the researchers reasoned, they could find out whether differing rates of sediment particles being deposited into the community had an effect on the ecosystem.

[Next up from climate change: Shell crushing crabs invading Antarctica]

They conducted three surveys in all: one in 1994, one in 1998 and the last in 2010. They found that there were major shifts over time in the species found in areas exposed to the most sedimentation, such as the inner station and deeper parts of the middle station. In these areas, the researchers observed a shift from immobile filter feeders, like the sea squirts, to more mobile animals who don’t rely on filter feeding for survival. But in the shallow parts of the middle station and in the outer station, where the particles weren’t such a problem, the researchers observed few changes.

Even from 1994 to 1998, there was a major observable shift in the inner and deep middle stations, which Sahade said was a surprise. “In only four years, the system changed drastically,” he said in an e-mail to The Post. “We had a completely different picture in which the most important species…and many of their accompanying fauna were severely reduced and some species almost disappeared. I can say this was completely unexpected and we were shocked.”

However, Smith — who was not involved with this study — said the results did not surprise him much. Smith was co-author on a 2013 paper that examined benthic communities along the West Antarctic Peninsula and predicted that an increase in silt, clay and other particles in the future, the result of glacial melting, would likely have a major impact on these hotspots of biodiversity. The new paper helps confirm his predictions.

“It’s the kind of thing that we would in general expect — a shift from suspension feeders to mobile deposit feeders and scavengers,” such as starfish or marine worms, he said. “And that’s what they’re seeing.”

In fact, at the time Sahade’s paper was published, Smith was on his way to Antarctica to conduct more research on the effects of sedimentation on Antarctic ecosystems. Continued work in this area is important because the effects are only likely to worsen in the future, as temperatures rise and glaciers continue to melt, he said — and these effects could have big implications for the marine ecosystem at large.

Antarctic sea-bottom communities, as they are now, are diverse places that attract many species, including krill. This makes them important feeding grounds for larger animals, such as whales. But that could change in the future.

“If this increased sedimentation from warming and glacial retreat occurs, it could fundamentally alter the biodiversity of coastal ecosystems along the Antarctic Peninsula,” Smith said.

And the scariest part is that these changes might be permanent.

“Sahade and his colleagues raise the disquieting possibility that the radical shift they saw would be irreversible even if the discharge of sediment stopped,” said Richard Aronson, professor and head of the department of biological sciences at Florida Institute of Technology, who was not a part of this study.

Sahade and his team theorize that shifts in benthic communities tend to occur suddenly — and once a new community of organisms is settled in, it’s difficult to go back to the way things were. Even if one were to remove all the extra sediment from one of these communities and return the water to its previous condition, the scientists aren’t sure how long it would take for the community’s original species to be able to come in and repopulate the area.

“Considering how rapidly ecosystems are changing in Antarctica, we may never have the opportunity to learn if they are right,” Aronson added. Particularly in West Antarctica, certain climate-related changes — such as the melting and impending collapse of the West Antarctic Ice Sheet — may already be unstoppable.

The study points to the urgent need for continued action to slow global warming and once again highlights its ever-growing list of consequences, particularly for the Earth’s polar regions.

In the meantime, monitoring bottom-dwelling ecosystems, like the one in this study, is one way of keeping an eye on the progressive effects of climate change. Benthic zones can be considered “sentinels” when it comes to climate change because they’re so diverse and sensitive, according to Sahade. And, threatened as they are, we’re only just beginning to understand their significance — which makes their continued study all the more important.

“We are far from knowing the potential of all these species that can disappear even before we know about them,” Sahade said.