​Melting sea ice may open polar oceans to new predators

​Melting sea ice may open polar oceans to new predators

5 October 2017 news

Melting sea ice may open polar oceans to new predators

New publication on the consequences of melting sea ice by Tom J. Langbehn (University of Bergen) and Øystein Varpe (Akvaplan-niva/UNIS). Link to the publication below. 

An article about the project in the Ecological Society of America, by Patrick Monahan 

Images of gaunt polar bears (Ursus maritimus) sitting on tiny chunks ofsea ice provide a poignant reminder ofArctic ecosystems’ vulnerability toclimate change. But a new paper byTom Langbehn (University of Bergen,Bergen, Norway) and Øystein Varpe(Akvaplan-niva/University Centre in Svalbard, Longyearbyen, Norway) suggests that melting sea ice may also alter Arctic ecosystems in a less obvious way: by letting sunlight penetrate deeper into the ocean. Sea ice in polar regions acts like an umbrella, blocking the Sun’s rays from reaching the ocean below. When that ice recedes, the underwater environment becomes brighter, allowing predatory fish to see farther through the water column. A fish can’t eat food it can’t find – so for planktivorous species like Atlantic herring (Clupea harengus), “water clarity may be as important as or more important than the number of prey”, explains Stein Kaartvedt (University of Oslo, Oslo, Norway), a marine biologist who was not involved with the study. Using decades of sea-ice measurements from locations across the Barents and Bering seas, Langbehn and Varpe modeled how the changing environment has affected the hunting ability of these predators. They found that fish can already see farther than they could in the 1970s, due to an ongoing decrease in ice cover. And if the ice ever melts completely, the researchers estimate thatthe visual range of these predators will increase by a factor of four in some areas, allowing them to scan the water sixteen times faster – and likely consume much more plankton – than they do now.

Fish that are fast-moving and swim in schools for protection are best suited to take advantage of these more favorable hunting conditions. “Those traits make them likely winners of sea-ice loss, as they can exploit the summertime and move out during winter when light remains dim regardless”, says Langbehn. By competing with bottom-dwelling Arctic fish, these new migrants could disrupt the flow of energy and food between different zones of the ocean depths. “People have been thinking in a particular way about climate change – there’s been so much focus on temperature”, while other factors like light have been comparatively ignored, explains Kaartvedt. “It’s an interesting idea.” But both Kaartvedt and Langbehn stress that these are far from the only expected impacts of receding sea ice on Arctic food webs, so future outcomes are difficult to predict.