Adelies Ross Sea ice floes
February 27, 2014

Rising Temperatures, Changing Wind Patterns Could Affect Predator-Prey Relationships In The Ross Sea

April Flowers for - Your Universe Online

The Ross Sea is a major, biologically productive ecosystem in the Antarctic, which "clearly will be extensively modified by future climate change" in the coming decades as longer periods of ice-free open water are created by rising temperatures and changing wind patterns. According to a new paper funded by the National Science Foundation (NSF), these ice-free periods affect the life cycles of both predators and prey.

The research team, which included four scientists from the Virginia Institute of Marine Science (VIMS) at the College of William and Mary and the Center for Coastal Physical Oceanography at Old Dominion University, used information drawn from the Regional Ocean Modeling System, a computer model of sea-ice, ocean, atmosphere and ice-shelf interactions. Their findings were published in a recent issue of Geophysical Research Letters.

The team concedes that "predicting future changes in ecosystems is challenging." However, they think that the changes predicted by their model have the potential to create "significant but unpredictable impacts on the ocean's most pristine ecosystem."

The ecological balance at the base of the Antarctic food web — including changes in distributions of algae, shrimp-like krill and Antarctic silverfish — will be affected by the wind and temperature changes. Disturbances in this balance may be expected to cause disruptions in the upper portions of the food web as well, including penguins, seals, and whales, which depend upon those lower species for food.

Walker O. Smith, Jr., professor of Marine Science at VIMS, led the study. He said, "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. Without a doubt the Ross Sea 100 years from now will be a completely different system than we know today."

The US Antarctic Program (USAP), managed by the NSF, coordinates all US research on the Southernmost Continent and in the Southern Ocean. USAP also provides the necessary logistical support for that research. This study was funded by NSF's Geosciences Directorate's Polar Programs and Ocean Sciences divisions.

Over the last half a century, the distribution and extent of Antarctic sea ice — ice that floats on the ocean surface — have shown drastic changes, including a documented decrease of sea ice in the Bellingshausen-Amundsen sector, but an increase of sea ice in the Ross Sea sector of Antarctica.

The authors say that observations show that "the duration of ice-free days on the Ross Sea continental shelf has decreased by over two months over the past three decades." This might have had effects on the current balance of biological productivity and the roles of various plant and animal species in the ocean ecosystem.

"Future projections of regional air temperature change, however, suggest that substantial warming will occur in the next century in the Ross Sea sector," while predictions show wind speeds increasing in some areas while decreasing in others.

"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."

According to the model, however, summer sea ice in the Ross Sea could decrease by more than half (56 percent) by 2050, and more than three-fourths (78 percent) by 2100. The summer mixing of shallow and deep waters in the region as a result of other changes is expected to decrease simultaneously.

Diatoms, the preferred food source of many plant-eating predators such as krill, would benefit from increased open water. However, some krill species, such as crystal krill, prefer a habitat with more ice. The ice is used as a hiding place from predators.

Minke whales, Adelie and Emperor penguins and crabeater seals all feed on crystal krill, and would have less food available if the population were reduced by more open water. The cycle doesn't stop there. Less sea-ice cover would allow more humpback whales to enter the Ross Sea in the summer to eat the krill. Adelies would be more vulnerable to leopard seal predation because they would have to travel further from their nests to prey on the silverfish, which are normally found at the ice edge.

The team concedes that it is challenging to know exactly what changes will take place in the Ross Sea ecosystem. If the model predictions are correct, however, 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."