Arctic marine species and ecosystems are undergoing pressure from a build up of changes in their physical, chemical and biological environment. These pressures, such as ice loss, changes to food, invasive species and infectious diseases, ‘are taking their toll on marine animals and are pointing to an ecosystem on the verge of a shift,’ says a report by the Conservation of Arctic Flora and Fauna (CAFF), a working group of the Arctic Council.
The report combined the observations of Arctic scientists all over the region. Key trends included:
• Increases in the frequency of contagious diseases. Past examples include incidences of bird cholera in the northern Bering Sea and the Arctic Archipelago and a mass death of seals and walruses in 2011 - the first designated Unusual Mortality Event in the US Arctic.
• Reductions in ice-dependent species as sea ice retreat occurs earlier and the open water season is prolonged. Marine species are already change their behaviour due to the lack of ice, Beluga whales in Hudson Bay (Canada) have changed their migration times, while walruses are increasingly using coastal haul-out sites instead of ice. Less ice is also probably linked to declines in hooded seal populations and lower reproduction rates in in Northwest Atlantic harp seals. ‘Extirpations - or local extinctions - of some ice-dependent seals are possible,’ reads the report, ‘but is expected to vary locally because of large regional variation in ice cover decline.’
• Reduced food resources for many Arctic species in marine environments. Animals are often transitioning to more terrestrial diets, or travelling further to find prey. Ivory gulls have declined alongside reductions in their sea ice hunting areas. Barents harp seals have reduced body fat associated with less food availability, while ground-nesting common eiders and cliff-nesting murres are being increasingly hunted by polar bears.
• An increasing diversity of southern species are moving into Arctic waters. These could increase competition and reduce the survival of endemic species. Observed southern species include Atlantic cod and killer whales.
‘We are used to changes in the Arctic, those have been building for quite some time now,’ says Kit Kovacs, a marine mammalogist who contributed to the report. ‘What we are not used to is the increasing rate of change - scientific modelling is barely keeping pace with the changes that are being observed in parts of the region.’ She is concerned about animals that rely on high Arctic conditions such as stable ice and good snow cover. ‘Ringed seals are tough animals and are long lived, but they haven’t reproduced normally in Svalbard since 2005 and that is bound to have knock-on effects for polar bears who rely on them for food.’ Already, decreasing sea ice has forced polar bears to transition towards a land-based diet, which contains less energy.
A warmer Arctic is creating opportunities for species usually found at lower latitudes. ‘We are seeing really dramatic changes in the distribution of animals, there are species coming up from the south such as capelin and killer whales,’ she says. ‘We have even had blue whales that are coming up to 80 degrees north.’ Often, the larger mammals are following their prey, such as krill, which has expanded its range with the new warmer temperatures.
‘Though these ‘new’ species could increase the biodiversity of the Arctic for a time, they would also put further stress on endemic Arctic animals, which are often dealing with changes to environment already,’ Kovacs concludes. ‘This kind of competition will unfold over the the next one or two decades. They are natural expanses of range in response to changes in environment - but they are occurring at the unnatural pace of anthropogenic warming.’