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  • As many as half of Earth's species may be

  • already migrating to escape warming temperatures.

  • Plants are inching northward

  • and so are many animals.

  • The Arctic ecosystem is particularly vulnerable to invasion.

  • Scientists aboard this research ship are hunting

  • the most important fish in the Arctic: polar cod.

  • Mixed in with the Arctic fish are invaders

  • including Atlantic cod and capelin.

  • The southern species compete for polar cod's food.

  • So here is a very typical Arctic food web

  • or food chain.

  • This food web is changing now.

  • These fish are among many species

  • migrating into the warming Arctic.

  • Relatively few species have evolved

  • to survive its frigid darkness.

  • Polar cod have some of the most impressive

  • adaptations to survive.

  • They use a trick that's common among arctic animals,

  • they store lots of fat in their bodies.

  • Polar cod eat tiny copepods,

  • which also store fat to survive the long winter.

  • And a high energy meal is crucial

  • for surviving the harsh Arctic.

  • One trawl after another reveals southern interlopers.

  • Out of a thousand fish caught in this trawl,

  • roughly 70% by weight are southern species.

  • It's hard for the scientists to pinpoint precisely

  • when we cross the boundary

  • between Atlantic and Arctic waters,

  • but that boundary has been slowly creeping northward.

  • Scientists call this process

  • the 'Atlantification' of the Arctic.

  • Atlantic waters are saltier and they mostly lack ice.

  • The biggest difference?

  • Atlantic water is as much as seven degrees warmer.

  • The polar Cod likes the colder water,

  • but it's losing territory.

  • Polar Cod flourish in the shallow waters

  • of the Barents Sea, but further north it's too deep for them.

  • Meanwhile, the warmer waters bring with them

  • new species that are shaking up the food web.

  • Along with new fish, there are Atlantic varieties of copepods.

  • They store much less fat than copepods native

  • to the Arctic, making them a less nutritious food source.

  • That means polar cod may have to spend more energy hunting.

  • For the same amount of animals that are gonna be eaten,

  • you don't transfer the same amount of energy.

  • Capelin, as well as Atlantic Cod,

  • were among the invaders we just caught in the trawl.

  • Capelin will also feed on the same prey

  • as the polar cod, so we start adding competition

  • between these two species.

  • The Atlantic Cod goes one step further:

  • it eats the polar cod itself.

  • Capelin's not as rich as polar cods, so that goes

  • or diminishes, then these levels will also be impacted.

  • It's easy to vilify the southern species

  • threatening the ecological balance here.

  • But take the Atlantic cod,

  • in their natural habitat, overfishing and now

  • rising temperatures have decimated its population.

  • So here in the Arctic, Atlantic Cod seems like an invader,

  • but it's also a climate refugee from the south

  • and its main predator is another

  • key species advancing northward.

  • Historically, most humans who have come to the Arctic

  • have taken a lot more than data and a few samples.

  • For at least 45,000 years, people have been coming

  • to this paradoxical region.

  • Punishing, desolate but rich with resources.

  • Humans are the Arctic's ultimate apex predator

  • and yet we're only getting started.

  • With countries like Norway extracting fossil fuels offshore,

  • other sectors are also expanding northward.

  • From tourism, to shipping, to military operations.

  • So the stressers in the Arctic

  • are probably going to intensify.

  • As the climate here changes

  • so will the meaning of the word Arctic.

  • For the animals who, for now, call it home.

As many as half of Earth's species may be

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为什么大西洋鱼类入侵北极(Why Atlantic fish are invading the Arctic)

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    joey joey 發佈於 2021 年 05 月 16 日
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