Plankton bloom in the Barents Sea. Photo: Envirisat, European Space Agency Photo: Jenny E. Ross/naturepl.com 

Food resources are being lost for many Arctic species in Arctic marine environments.

Many species have to travel further and expend more energy to feed, leading to concerns about individual health and potential effects at the population level.

• Ivory gull declines coincide with reduction in their sea ice feeding areas.
• Reduced ice cover has also led to increased polar bear predation on ground-nesting common eiders and cliff-nesting murres, potentially leading to local population declines.
• Black guillemots in Alaska feed at the ice edge and have been forced to travel greater distances to foraging areas as sea-ice retreats, leading to lower breeding success.
• Barents Sea harp seals have reduced body condition associated with reduced food availability as their travel time to the ice edge to feed is longer.
• Some Indigenous communities have noted a change in walrus stomach contents, with more open water fishes and less clams, indicating that the distribution and availability of benthic resource species are changing in some areas.

 Capelin. Photo: Carsten Egevang/ARC-PIC.com Seabirds on cliff. Photo: Morten Ekker

Some Arctic species are shifting their ranges northwards to seek more favourable conditions as the Arctic warms.

These movements pose unknown consequences for Arctic species and their interactions, such as predation and competition.

• The northward expansion of capelin has led to changes in seabird diet in northern Hudson Bay. It also may affect marine mammals.
• Warming can have surprising and contradictory effects on species e.g. rising temperatures in the Chukchi Sea have been associated with an increase in nutritious copepods with high fat content.

 Greenland halibut. Photo: Fernando Ugarte Amphipoda Cleippides quadricuspis. Photo: Olga Zimina, Greenland Institute of Natural Resources 

Northward movement is easier for more mobile open-water species.

Open water species such as polar cod, are more mobile compared to those linked to shelf regions, such as benthic species including some fishes for which suitable habitat may be unavailable if they move northward.

• Greenland halibut have the potential to expand into the Arctic Basin with climate change, but only given the availability of suitable prey and topography.

 Atlantic cod. Photo: Peter Prokosch Killer whale. Photo: Alberto Loyo/shutterstock.com

Increasing numbers and diversity of southern species are moving into Arctic waters.

In some cases, they may outcompete and prey on Arctic species, or offer a less nutritious food source for Arctic species.

• The boreal copepod Calanus finmarchicus is expanding north from the Atlantic and replacing its more nutritious Arctic relatives C. glacialis and C. hyperboreus.
• Complex patterns of benthic biomass change in the Barents Sea are related to, amongst other pressures, warming of the Barents Sea improving conditions for boreal species to move further north.
• The distribution of Atlantic cod is expanding in the Atlantic Arctic and increasing predation pressure on the polar cod, an important nutrient-rich prey fish, important for other fishes, seabirds and marine mammals, especially seals.
• The more temperate killer whale is expanding in Arctic waters and may compete with other apex predators for nutritious seals.

 Walrus. Photo: USFWS Walrus haul out on Round Island, Alaska. Photo: USFWS, Alaska

Current trends indicate that species reliant on sea ice for reproduction, resting or foraging will experience range reductions as sea ice retreat occurs earlier and the open water season is prolonged.

• Since the 1980s, ice amphipod abundance has declined around Svalbard and it is possible that sea ice algal community structure has changed in the central Arctic.
• Although there are no documented cases of widespread population changes, some Arctic-breeding seabirds and some resident marine mammals have been observed shifting behaviours.
• Ducks breeding on the Siberian tundra and wintering at sea have shortened migration in response to declines in winter sea ice cover.
• Belugas in Hudson Bay varied timing of migration in response to variations in temperatures. These migrations may affect the ability of people to find and use these resources.
• Changes in sea ice conditions are probably linked to declines in the abundance of hooded seals, lower reproduction rates of Northwest Atlantic harp seals, reduced body condition of Barents Sea harp seals, and changes in prey composition of bearded seals.
• Extirpation of some stocks of ice-dependent seals are possible, but is expected to vary locally because of large regional variation in ice cover decline.
• Early spring sea ice retreat also reduces suitable breeding and pup rearing habitat for ringed seals. This affects the ability for polar bears, which feed on ringed seals, to rebuild energy stores after fasting during their own breeding period.
• Historically, walruses rested on sea ice located directly over prime feeding areas, but due to late season ice formation are increasingly using coastal haul-out sites instead of sea ice. In addition to travelling further to access foods, this also increases the risk of calf mortality due to stampede.

 Polar bear looks on as a ship passes through Arctic waters. Photo: Garry Donaldson Seastar. Photo: Caitlin Bailey GFOE The Hidden Ocean 2016, Chukchi Borderlands

Arctic marine species and ecosystems are undergoing pressure from cumulative changes in their physical, chemical and biological environment.

Some changes may be gradual, but there may also be large and sudden shifts that can affect how the ecosystem functions.

• It is hard to determine where and when these “tipping points” exist because the Arctic marine environment experiences a variety of stressors and subsequent reactions that can interact in complex and surprising ways. For those charged with managing natural resources and public policy in the region, it is crucial to identify the combined effects of stressors and potential thresholds to prepare effectively for an uncertain future.

 Common eiders weathering a storm on a polynya. Photo: Grant Gilchrst Inuit man cuts up seal. Photo: Carsten Egevang/ARC-PIC.com

Increases in the frequency of contagious diseases are being observed.

• Incidents of avian cholera have increased in the northern Bering Sea and Arctic Archipelago.
• The first designated Unusual Mortality Event in the U.S. Arctic occurred in 2011 and involved species of seals and walrus essential food resources affecting coastal community health, nutrition, cultural and economic well-being in areas of Canada, U.S., and Russia.