For much of the year, a layer of sea ice covers the Arctic Ocean. It builds up in winter. Come summer, the sea ice thins or shrinks in overall size. But 2016 has been a really warm year, which has led to far less sea ice than normal. So the Arctic is on track this year to match or perhaps even exceed the record low summertime sea ice seen in September 2012, scientists say. A new study shows why this could be a big problem for life in and around the Arctic.
Disappearing sea ice is a symptom of a warming planet. It also poses risks to the life associated with that ice. That includes the algae that live in brine-filled channels within this ice.
“These algae are adapted to grow under very low light conditions,” says Doreen Kohlbach. She is a marine biologist at the Alfred Wegener Institute in Bremerhaven, Germany. These algae are some of the species that form the base of the Arctic food web. And they are an important source of food even for species that don’t live under the ice, her team now reports.
Climate change could therefore be a big problem for the Arctic ecosystem. That’s because a loss of ice there will affect more than just the organisms that have a close connection to the ice. It also will affect life in the open ocean, Kohlbach says. This is a region known as the pelagic (Peh-LAAJ-ik) zone.
Zooplankton are tiny creatures that eat algae and other simple ocean species. For its new study, Kohlbach’s team looked at various species of zooplankton during late summer. Some of these tiny critters live near the sea ice. Others are pelagic. The researchers determined how much of their diet had come from sea-ice algae. To do that, they looked for markers of the algae. These were building blocks of the algae known as fatty acids. If they showed up in the zooplankton, it was sign these small animals had dined on the algae.
Animals that lived beneath the sea ice got a lot of their energy — sometimes described in terms of carbon (an ingredient in everything they eat) — from ice algae. Indeed, 60 to 90 percent of their meals had consisted of the algae,. But even pelagic species “showed a significant dependency” on ice algae, notes Kolbach. Those animals got 20 to 50 percent of their dietary energy from algae that had been embedded in sea ice.
The researchers described their findings July 8 in Limnology and Oceanography
Scientists have yet to look for markers of algae higher up in the food web — in bigger animals that may have dined on the zooplankton. So for now, the scientists can’t yet predict how the loss of sea ice algae might affect larger species, such as fish, seals or polar bears. But they, too, will likely be affected, Kohlbach says. If falling summer sea ice affects life at the bottom of the food web, she says, eventually it also will affect those higher up.
There’s also a chance that species could switch to dining on other species if their preferred sea-ice algae disappear. But the concern is that some species might not be able to make that switch, Kohlbach says. “To determine the consequences on a species-level, we need to do more research.”
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algae Single-celled organisms, once considered plants (they aren’t). As aquatic organisms, they grow in water. Like green plants, they depend on sunlight to make their food.
Arctic A region that falls within the Arctic Circle. The edge of that circle is defined as the northernmost point at which the sun is visible on the northern winter solstice and the southernmost point at which the midnight sun can be seen on the northern summer solstice.
behavior The way a person or other organism acts towards others, or conducts itself.
brine Water that is salty, often far saltier than seawater.
carbon The chemical element having the atomic number 6. It is the physical basis of all life on Earth. Carbon exists freely as graphite and diamond. It is an important part of coal, limestone and petroleum, and is capable of self-bonding, chemically, to form an enormous number of chemically, biologically and commercially important molecules.
climate The weather conditions prevailing in an area in general or over a long period.
climate change Long-term, significant change in the climate of Earth. It can happen naturally or in response to human activities, including the burning of fossil fuels and clearing of forests
colleague Someone who works with another; a co-worker or team member.
fatty acid A large molecule made of up chains of carbon and hydrogen atoms linked together. Fatty acids are chemical building blocks of fats in foods and the body.
food web (also known as a food chain ) The network of relationships among organisms sharing an ecosystem. M ember organisms depend on others within this network as a source of food.
limnology A branch of ecology that studies inland waters, including lakes, streams and groundwater. A scientist who works in this field is called a limnologist.
marine Having to do with the ocean world or environment.
marine biologist A scientist who studies creatures that live in ocean water, from bacteria and shellfish to kelp and whales.
marker (in biomedicine) The presence of some substance that usually can only be present because it signals some disease, pollutant or event (such as the attachment of some stain or molecular flag). As such, this substance will serve as a sign — or marker — of that related thing.
molecule An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).
oceanography (adj. oceanographic ) The branch of science that deals with the physical and biological properties and phenomena of the oceans. People who work in this field are known as oceanographers.
organism Any living thing, from elephants and plants to bacteria and other types of single-celled life.
pelagic An adjective for life or conditions in the open ocean. These are regions far from coastlines and often deep below the surface.
planet A celestial object that orbits a star, is big enough for gravity to have squashed it into a roundish ball and it must have cleared other objects out of the way in its orbital neighborhood. To accomplish the third feat, it must be big enough to pull neighboring objects into the planet itself or to sling-shot them around the planet and off into outer space. Astronomers of the International Astronomical Union (IAU) created this three-part scientific definition of a planet in August 2006 to determine Pluto’s status. Based on that definition, IAU ruled that Pluto did not qualify. The solar system now includes eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
sea An ocean (or region that is part of an ocean). Unlike lakes and streams, seawater — or ocean water — is salty.
species A group of similar organisms capable of producing offspring that can survive and reproduce.
symptom A physical or mental indicator generally regarded to be characteristic of a disease. Sometimes a single symptom — especially a general one, such as fever or pain — can be a sign of any of many different types of injury or disease.
zooplankton Small organisms that drift in the sea. Zooplankton are tiny animals that eat other plankton. They also serve as an important food source for other marine creatures.
D. Kohlbach et al. The importance of ice algae-produced carbon in the central Arctic Ocean ecosystem: Food web relationships revealed by lipid and stable isotope analyses. Limnology and Oceanography. Published online July 8, 2016. doi: 10.1002/lno.10351.