August 2, 2013
Wildlife Greatly Impacted By Arctic Sea-Ice Loss
April Flowers for redOrbit.com - Your Universe Online
Because sea ice is at its lowest point in 1,500 years, scientists are questioning how ecological communities in the Arctic will be affected by this continued and perhaps accelerating melting process over the next two decades.
An international team of scientists, led by Penn State University biologist Eric Post, examined relationships among algae, plankton, whales, and terrestrial animals such as caribou, arctic foxes, and walrus, as well as the effects of human exploration of previously inaccessible parts of the region, to understand the answers to this question. Their findings were published in a recent issue of Science.
"Our team set out to explore the 'domino effect' of sea-ice loss on marine animals, as well as on land-dwelling species living adjacent to ice," Post said. "Arctic sea ice should be thought of as a biome or an ecosystem and the effects of melting and warming on microorganisms living under ice in this biome already have received much attention. However, those animals living near the ice likely are feeling the effects, as well."
The sea ice is expected to continue to melt at an accelerating rate, even after reaching a record low in August of 2012. Over the entire period covered by the record, Arctic sea ice has declined by more than [51,000 square miles] -- a space slightly larger than the state of South Carolina -- per year," Post said. "That's an area of critical habitat for many species and the rate of loss is increasing."
An acceleration of this rate, added Post, will likely be due, in part, to the loss of albedo -- the white surface provided by ice that reflects sunlight -- thereby causing a cooling effect. The much less reflective, darker surface of open water will replace the high albedo of the ice. This will accelerate warming, which will accelerate the melting.
"By viewing sea ice as essential habitat and a substrate for important species interactions, rather than as a lifeless blank surface, its loss as a result of warming becomes a rather stunning prospect," Post emphasized.
EFFECTS ON TERRESTRIAL LIFE
The sea-ice melting will have a domino effect on terrestrial animals, according to Post, which could occur in the following manner through a disruption in the food chain: Sea-ice algae and sub-ice plankton, which together account for 57 percent of the total annual biological production in the Arctic Ocean, already are being immediately affected by sea-ice melting because ice loss triggers a significant change in the blooming times of these organisms. Lands adjacent to areas of sea-ice loss will likewise experience significant surface warming inland from the coast line. This will affect soil conditions and plant growth. Invertebrate ocean-dwelling animals such as zooplankton that feed on algae and phytoplankton in the seas are already being affected. The research team suggests larger terrestrial animals such as caribou could also find their land-dwelling food sources disrupted because of temperature changes affecting plant communities inland.
"A change in population mixing could be another, indirect effect of sea-ice melting," Post said. Wolf and arctic fox populations that are currently isolated only in summer could be even more isolated by longer periods of the year without ice. The ice allows travel between populations, so the loss of ice could lead to a decline in crossbreeding.
The effect of sea-ice loss could be just the opposite for other species. "We know that, for some species, sea ice acts as a barrier to intermixing," Post explained. "So ice loss and a lengthening of the ice-free season likely will increase population mixing, reducing genetic differentiation." This mixing of populations (hybridization) has already occurred between polar and grizzly bears. Polar bears are now spending more time on land where they have contact with the grizzlies.
Such mixing of populations is not necessarily cause for concern, according to Post, but it could lead to drastic changes in disease dynamics. Populations hosting a certain pathogen could transfer it to previously unexposed populations, Post explained. "In addition, a decrease in sea ice in arctic Canada likely will increase contact between eastern and western arctic species, promoting mixing of pathogen communities that previously were isolated," Post said. "For example, phocine distemper virus (PDV) currently affects eastern Arctic seals. But if these seals begin to mix with western arctic seals, the virus may reach other, naive populations."
Further challenges to the health and vitality of some species' populations could be challenged by the mere overcrowding of animals in coastal habitat as the sea ice retreats. Post noted this is especially true for walrus.
"Walrus are benthic feeders ... which means they are specialists in foraging for food that occurs only in shallow waters," said Post. "They also use the edge of the sea ice to rest and dive from while foraging. However, as sea ice melts and its edge retreats from the shoreline, it becomes located above deeper water. As a result, walrus have been observed abandoning the retreating ice edge and congregating along shorelines, from which they can try to maintain access to shallow water. This behavior, however, increases the local density of animals on such 'haulouts,' and can promote transmission of pathogens as well as lead to trampling of young."
Previously remote areas of the Arctic will have greater accessibility to humans, causing yet another unexpected consequence. "Retreating sea ice, longer ice-free seasons, and loss of sea ice are expected to promote development of shipping lanes and increased shipping traffic in areas that formerly were rather inaccessible," Post said. "This increased marine access likely will accelerate the pace of mineral and petroleum exploration in the Arctic, which in turn could affect both terrestrial and marine animals; for example, bowhead whales and Pacific walrus."
The study was funded by the National Science Foundation (NSF), and in part, by the Polar Center at Penn State through the Penn State Institutes of Energy and the Environment.
In addition to Post, the research team consisted of Jeffrey Kerby, a graduate student in the ecology program at Penn State; Uma Bhatt and Donald A. Walker from the University of Alaska in Fairbanks; Cecilia Bitz from the University of Washington; Jedediah Brodie from the University of British Columbia in Vancouver, Canada; Tara L. Fulton from the University of California in Santa Cruz; Mark Hebblewhite from the University of Montana; Susan Kutz from the University of Calgary; and Ian Stirling from the University of Alberta in Edmonton, Canada.