Polar Ecology

Woodcut by Aron of Kangeq, Nuuk, 1860 Off Ilulissat, Greenland FREDRIK EHRENSTRÖM STEFAN LUNDGREN Svalbard KUBUS 35 Polar Ecology The polar bear is hungry. Using her sensitive nose, she searches for a seal. She spots one lying on the ice, and as she creeps closer, her steps become careful. The seal has good hearing, good eyesight, and a good sense of smell. It is ready to dive into the water as soon as it senses danger nearby. So, very stealthily, the polar bear puts one paw in front of the other in the snow until she is only 30 meters from her prey. Her final rush is an explosion of energy, and she pounces on the seal. This time, luck is with her, and she enjoys a good meal of seal blubber, her favorite food. The rest of the seal is left behind when she moves on over the ice, but close behind comes the Arctic fox, like a shadow waiting for its share. This meal on the ice illustrates two key points in discussing contaminants in the Arctic. Predation is the pathway by which contaminants move from animal to animal in Arctic food webs. Moreover, it is no coincidence that the polar bear is a picky eater when hunting is good, choosing only the blubber and leaving the rest of the seal. Energy is important for sur- vival in cold environments and a preference for fatty foods is one of many adaptations shown by Arctic animals. This chapter discusses plant and animal life in the Arctic, with a focus on adaptations that can make Arctic ecosystems especially vulnerable to contaminants. It also describes food webs on land, in lakes and rivers, and in the sea, including brief life histories of some species that appear throughout this report. Faroe Islands 36 Arctic conditions The cold creates a lack of nutrients Polar ecology A cold climate and long, dark winters have Reduced microbial activity also limits the rate profound effects on the environment in which at which nutrients can cycle in Arctic ecosys- animals and plants try to survive. In addition, tems. In cold, continental regions it has been the productive season is short, which means estimated that a 95 percent turn-over of organic that there is limited time to reproduce and to matter takes more than 300 years. Carbon gather stores of energy. Climatic conditions are thus accumulates in the soil, and many nutri- most severe in the northern parts of the AMAP ents remain bound and unavailable. The slow region, while some of its southern areas are degradation processes lead to deficiencies in better described as subarctic or even northern many key nutrients in both terrestrial and lake temperate, having fewer of the limitations typi- ecosystems. Plant growth is often limited by cal of the polar region. lack of nitrogen and phosphorus, along with the low temperatures. Low temperatures Low temperatures also limit the chemical slow down biological processes weathering of bedrock, a process which sup- plies nutrient ions to the soil. Slow weathering The Arctic is synonymous with cold. The effects rates can be compounded by permafrost. of low air temperatures are increased by the The ecosystems of the marine surface layer fact that, in spring, the sun has to melt snow are characterized by large variations in nutri- and ice before it can start to warm the ground. ent availability, both regionally and seasonally. Most biochemical processes are tempera- A substantial portion of the nutrients avail- ture-dependent, and the rate of biological able to Arctic ecosystems comes from upwel- activity slows down at temperatures below a ling of water from water masses of southern certain level. Although adapted to a cold cli- origin, inputs from large rivers, and aerial mate, many plants and some animals in the deposition. These pathways tend to carry Arctic grow more slowly than they would else- organic matter, nutrients, and contaminants. where. For example, in Davis Strait, the transi- tion from male to female in northern shrimp, Snow and ice limit available light which is part of normal development, takes four to five years, in contrast to two to three Low temperatures also create conditions for years in the North Sea. Microbial life in soil extensive ice cover on seas and lakes and for and in the waters and bottom sediments of snow cover on land. Even if summer brings lakes, rivers, and the ocean is similarly re- 24-hour daylight to the area north of the Arc- stricted by low temperatures, slowing the tic Circle, ice and snow limit the amount of breakdown of organic material. light that can reach plants and plankton. As This slow degeneration is apparent in well- much as half of the total annual input of solar preserved artifacts from ancient Arctic cultures energy arrives before the end of snowmelt, so as well as in the long life of garbage left on the that much of it is reflected back into space. tundra or of oil spills. It also makes the envi- Some organisms, such as ice algae, live in ronment slow to recover from physical de- crevices in the snow and ice and can quickly The ice alga Melosira struction connected with exploitation of re- take advantage of the light in spring. Other arctica in old ice. sources, human settlement, and overgrazing. organisms are adapted to low-light conditions under the ice. Generally, however, solar energy has to melt snow and ice before it can be uti- lized by plants. Therefore, in spite of the long days and midnight sun, the growing season in the Arctic is short. In the High Arctic, snowmelt is usually not completed until the end of June, after the summer solstice, and fresh snow may come in August, leaving a growing season as short as one to two-and-a-half months. In the Low Arctic, the growing season can last three to four months. For Arctic lakes, the open water period is also short. Lakes might be ice-free for only one to two months, and in cold years, the ice may not disappear at all. In the subarctic, the ice- free season for freshwater ecosystems can be four to six months. In the marine environment, sea ice and snow on top of the ice also limit energy input. Even before all the ice has melted, however, enough light penetrates to initiate phytoplank- BJØRN GULLIKSEN ton production. The sea ice starts to break up in May and June, and begins to form again in them for several months with little food. The 37 September. In some inlets and straits of the most efficient way to store energy is by produ- Polar ecology high-latitude regions, ice can remain unbroken cing fats, and Arctic organisms have an unusual for several years and vast areas of the Arctic propensity to produce and accumulate fat. Ocean are always covered by pack ice, limiting Such dependence on fats has negative conse- biological productivity. In the subarctic, sea-ice quences when environmental toxins enter the cover varies greatly depending on ocean cur- scene. Many organic toxins, such as pesticides rents, as described in the chapter The Arctic. and PCBs, are highly fat-soluble and therefore accumulate in the fat reserves of animals, such as the blubber of seals. When food becomes Freshwater comes in one short spurt scarce, these fat reserves are used but the cont- Most precipitation in the Arctic falls as snow, aminants remain, and their concentrations and most water becomes available during the increase in the remaining fat. two-to-three week snowmelt period. The cold In freshwater systems, spring runoff carries air does not allow much moisture to evaporate both nutrients and contaminants into streams, and permafrost often keeps it from draining ponds, and lakes. In the marine environment, into the ground. The water from snowmelt the melting sea ice plays a similar role. Thus, and summer rains therefore creates extensive the burst of productivity in the spring, when wetlands on the tundra of the Low Arctic. nutrients and energy are available, can provide In the High Arctic, soils are often thin and an efficient uptake route for contaminants. can hold little moisture. Snowmelt ends abruptly and small streams often run dry later Perennial plants save their nutrients in the summer. In High Arctic desert areas, lack of water can limit biological productivity. The lack of nutrients in the terrestrial land- scape has favored plants that preserve their nutrients from one season to the next. In con- Glaciers have created trast to the numerous annual species of south- an evolutionary frontier ern ecosystems, Arctic vegetation consists Parts of the polar region have undergone mostly of perennial plants. Many keep their numerous glaciations over the past 1.8 million leaves over winter. Those that do not, with- years. The most recent of these ended only draw nutrients to their stems and roots before 10000 years ago. Plants and animals, there- winter comes. This makes it possible for them fore, came to these areas fairly recently, and to begin developing shoots the following spring many of them are opportunistic, invading before the surrounding soil thaws, which is an species adapted to survive under a range of advantage in a short growing season. conditions. Many animals can adjust their Not shedding leaves can be a disadvantage feeding habits, growth rates, and reproduction if a plant is damaged by contaminants or other in response to variations in climate or food environmental stresses, such as ultraviolet availability. radiation. Damage in one year will affect This recent colonization by plants and ani- growth for years to come, and even a small mals, together with low ecosystem productiv- change can lead to large losses in productivity.

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