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Report: Ecosystem disruptions expected in Ross Sea

‘Portions of the food web that depend on ice in their life cycles will be negatively impacted, leading to severe ecological disruptions’

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How will changes in the Antarctic food chain affect aquatic mammals? bberwyn photo.

Staff Report

FRISCO — Climate change will fundamentally change The Ross Sea, one of Antarctica’s productive biological regions, but exactly how those changes will play out is hard to predict, scientists said after running computer models combining sea-ice, ocean, atmosphere and ice-shelf interactions.

The region is likely to experience ‘severe ecological disruptions,” a group of scientists wrote in their new study, explaining that rising temperatures and changing wind patterns will create longer periods of ice-free open water, affecting the life cycles of both predators and prey.

“The model suggests that the substantial changes in the physical setting of the Ross Sea will induce severe changes in the present food web, changes that are driven by global climate change,” said Walker O. Smith, Jr., a professor at Virginia Institute of Marine Science and the lead author of the study. “Without a doubt the Ross Sea 100 years from now will be a completely different system than we know today.”

The scientists concluded that the impending changes will affect the ecological balance at the base of the Antarctic food web–including changes in distributions of algae, shrimp-like krill and Antarctic silverfish. Those impacts will ripple up the food chain, causing disruptons to penguins, seals and whales.

Observations during in the last half century include changes to the distribution and extent of Antarctic sea ice. Sea ice decreases have been documented in the Bellingshausen-Amundsen sector even as sea ice expands in the Ross Sea region.

Significantly,  “the duration of ice-free days on the Ross Sea continental shelf has decreased by over two months over the past three decades,” which may have had effects on the current balance of biological productivity and the roles of various creatures and microscopic plants in the ocean ecosystem.

Under nearly any scenario, regional air temperatures will continue to warm, and winds will pick up, at least in some areas.

“These changes are expected to reverse the sea-ice trends in the future; however the projected changes in heat content on the continental shelf and ecosystems dynamics that will occur as a result of such changes remain far from certain,” the paper found.

Summer sea ice in the Ross Sea could decrease by more than half, or 56 percent, by 2050 and by more than three-quarters, or 78 percent, by 2100. At the same time, the summer mixing of shallow and deep waters in the region as a result of other changes is expected to decrease.

While increased open water would benefit diatoms, the preferred food source of many plant-eating predators such as krill, some krill species, such as crystal krill, prefer a habitat with more ice, which they use as a refuge from predators.

In turn, minke whales, Adelie and Emperor penguins and crabeater seals that feed on crystal krill would have less food available if the crystal krill population were reduced.

With less sea-ice cover, however, more humpback whales could enter the Ross Sea in the summer, increasing krill predation. Adelies, which prey on silverfish at the ice edge, would have to travel further from their nests and, as a result, be potentially more vulnerable to leopard seal predation.

While it is difficult to know specifically what changes the Ross Sea ecosystem will see, the model predictions, if they are accurate, suggest that they are likely to be far-reaching.

“Regardless of the exact nature of the alterations,” the researchers write, “substantial portions of the food web that depend on ice in their life cycles will be negatively impacted, leading to severe ecological disruptions.”

The research was funded by the National Science Foundation and published in Geophysical Research Letters.

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