Ecosystems
Arctic sea-ice ecosystem
Arctic_sea-iceArctic sea ice is a unique ecosystem providing habitat to many ice-associated species, including micro-organisms, fish, birds, and marine mammals. Although Arctic sea ice has decreased substantially in extent and thickness in recent years, the response of individual species to changes in sea ice depends on its ability to adapt and its natural history, as well as the scale of environmental change. Information to assess the status and trends of ice-associated species is very limited, and in some cases the relationship between sea ice and species is not entirely understood. Continued sea ice loss due to climate change is expected to lead to changes in the sea-ice ecosystem towards a pelagic, sub-Arctic ecosystem over a larger area. Increased production in open water may increase prey concentrations for some species, such as bowhead whales; however, with less ice there will be less ice algae, affecting bottom-feeding marine species. Continued warming and continued reductions in sea ice will likely result in the northward expansion of sub-Arctic species, with the associated potential for increase in disease, predation, and competition for food.
 
Greening of the Arctic
GreeningClimate change is impacting terrestrial Arctic ecosystems, with evidence showing that Arctic vegetation has undergone significant shifts in recent decades. There is an increase in productivity over much of the Arctic, as well as an increase in the length of the growing season. The northward movement of the treeline is encroaching on the southern margin of the tundra and could result in significant losses of tundra habitat by 2100. Climate warming is also likely to change the composition of plant communities. While the number of plant species inhabiting the Arctic may actually increase over the long term, the diversity of plants unique to the Arctic will probably decrease in abundance.
 
Reproductive phenology in terrestrial ecosystems
ReproductiveChanges in the timing of reproduction in plants and animals have been reported from the Arctic. There is some evidence indicating that the timing of reproduction – including the flowering of plants, emergence of insects, and egg-laying in birds – is occurring earlier in response to warming conditions and earlier snowmelt. Longer growing seasons may be an advantage to some species in terms of reproduction and growth. There is, however, a serious risk of disruptions in food webs when there is a “trophic mismatch”, where the breeding of some species (e.g., caribou or birds) no longer matches up with the timing of the most abundant and nutritious food (e.g., new plant growth or insects).
 
Appearing and disappearing lakes and their impacts on biodiversity
AppearingThermokarst lakes and ponds, formed by the thawing of permafrost, are the most abundant and productive aquatic ecosystems in the Arctic. They are areas of high biodiversity with abundant microbes, benthic communities, aquatic plants, plankton, and birds. While the disappearance and appearance of thermokarst lakes is a relatively common occurrence, there are concerns about their future in the face of climate warming. There has been a net decrease in the number of thermokarst lakes over the past fifty years in the western Canadian Arctic, Siberia, and Alaska. Trends in other Arctic regions are unknown. The appearance and disappearance of thermokarst lakes is projected to be more common with climate change and will likely lead to more aquatic habitat becoming available in higher latitudes over time. The effects of these habitat shifts on local aquatic populations, migratory species, and vegetation is the subject of further investigation.
 
Arctic peatlands
Arctic_peatlandsWetlands cover about 70% of the Arctic with the most extensive wetland types being non-forested and forested peatlands. Peatland species comprise 20–30% of the Arctic and sub-Arctic flora. Arctic peatlands also support biodiversity worldwide through bird migration routes. Seventy-five percent of the more than 60 bird species with conservation priority in the European part of the Arctic are strongly associated with tundra and mire habitats. Peatlands also provide crucial ecosystem services such as habitat maintenance, permafrost protection, and water regulation. Over recent years, the southern limit of permafrost in northern peatlands has retreated by 39 km on average and by as much as 200 km in some parts of Arctic Canada, with some of this attributed to climate change. The northward movement of the treeline will affect not only Arctic biodiversity through shifting habitats and species, but also reduce albedo (surface reflectivity), further enhancing warming of the atmosphere.
 
Effects of decreased freshwater ice cover duration on biodiversity
EffectsIce cover is an important component of northern freshwater ecosystems, influencing many physical, chemical, and biological processes. The duration of freshwater ice cover has decreased by an average of almost two weeks over the last 150 years, with earlier break-ups and later freeze-ups. As the climate warms, longer open-water conditions will prevail. Depending on the type and location of a water body, decreases in the duration of lake ice can be expected to have a range of ecological impacts from increased productivity and increased habitat availability with less ice to changing distributions and reduced habitat availability for some cold-water species of fish.
 
Changing distribution of marine fish
ChangingThere is evidence of changes occurring in the distribution of some fish species, specifically a northward shift of both bottom-dwelling and pelagic marine species, and in both exploited and unexploited fish stocks. Climate change is likely one of the reasons for the shifts, along with other factors such as fishing pressure. Temperature changes in the oceans can affect fish populations directly (e.g., shifting to areas with preferred temperatures) and indirectly (e.g., by impacting food supply or the occurrence of predators). Computer modeling using current climate change scenarios indicates that the distribution and abundance of Arctic fin, an important prey species, may be greatly reduced over the next 30 years. The implications of such changes on both marine ecosystems and the human societies dependent upon them are a cause for concern.
 
Impacts of human activities on benthic habitat
ImpactsCold-water coral reefs, coral gardens, and sponge grounds are areas of high biodiversity in the Arctic and have been identified as Vulnerable Marine Ecosystems (VMEs). Damage to these ecosystems may reduce local biodiversity. Also, because corals and sponges grow so slowly, recovery of these habitats may range from decades to centuries. These habitats are particularly vulnerable to human activities such as fishing and oil and gas exploration. Increasing sea temperatures, ocean acidification, and pollution present further threats to corals and sponges.