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The cause is further down in the abstract > Consequently the two temperatures defining the core of krill distribution (7–13 °C) were 8° of latitude apart 60 ye

The cause is further down in the abstract > Consequently the two temperatures defining the core of krill distribution (7–13 °C) were 8° of latitude apart 60 years ago but are presently only 4° apart. Krill lost 50% of their habitat in the last 60 years. This article has been added to my favorites because this is one piece of evidence that shows that climate change won’t just shift organisms north, but will result in reductions of species that will impact our ecosystems.

ajb 5y ago
Reduction from 8 degrees of latitude to 4 doesn't tell us the area reduction, because the area depends on the absolute distance from the pole. It's also not linear because if the outer radius changes, the change should be proportional to the square of the radius, so potentially more than 50%, or potentially no change or even growth, if the ideal thermal area moved outwards
- h0l0cube 5y ago
  Or you could click on the article and see for yourself, under the safe presumption that the researchers would do a more thorough job than the lay person. From the article, figure 2: > Mean spatial abundance of euphausiids per decade in the North Atlantic from 1958–2017 split into six time-periods 1958–1967; 1968–1977; 1978–1987; 1988–1997; 1998–2007; 2008–2017. https://www.nature.com/articles/s42003-021-02159-1/figures/2 https://www.nature.com/articles/s42003-021-02159-1/figures/2
xhkkffbf 5y ago
I realize that habitat loss is a big thing, but I also know that some krill-eating species like the big whales have rebounded over the last 60 years. Could this decline in krill be the result of the return of the whales?
- jheitzeb 5y ago
  Krill is a keystone species. Lose krill and the food chain collapses — at least krill is thought to hold such a role in the Southern Hemisphere. There, it is harvesting for omega 3 supplements that’s causing the decline. https://www.theguardian.com/environment/2008/mar/23/fishing.food https://www.theguardian.com/environment/2008/mar/23/fishing....
  - eloff 5y ago
    I think mostly the krill is used as fish and animal feed as a source of protein. Supplements are probably a small part of the consumption. It seems like a bad idea to overfish the base food chain species. But then pretty much everything we do with the ocean is a bad idea. The only thing that has been positive where the oceans are concerned is creating marine reserves where commercial fishing is prohibited, and enforcing that.
- aliasEli 5y ago
  It seems pretty unlikely. For all whale specious the numbers are far lower than historical numbers. There is a huge amount of krill and there are a lot of other species that have been doing this for a very long time.
pvaldes 5y ago
> Krill lost 50% of their habitat in the last 60 years. Not necessarily. Krill species live from surface to fairly deep waters. Surface is an important, but small part on its entire habitat. We need to take in mind that all in this study is about the situation found when sampling an area between 0-10m deep. For Thysanoessa for example this means that if you don't find them at the surface there is still a 390m deep layer where they could still be located. Meganyctiphanes, Nematobranchion and Thysanopoda concentrate normally in waters below 400m by day (Saunders et al, 2013). They can migrate to surface [1] at night, but can also choose to remain close to the sea bottom in much deeper areas. It depends a lot on the species, location and time of the year. [1] More or less, surface does not mean 0m necessarily, can mean -15m or -20m also.

ajb 5y ago

Reduction from 8 degrees of latitude to 4 doesn't tell us the area reduction, because the area depends on the absolute distance from the pole. It's also not linear because if the outer radius changes, the change should be proportional to the square of the radius, so potentially more than 50%, or potentially no change or even growth, if the ideal thermal area moved outwards

h0l0cube 5y ago
Or you could click on the article and see for yourself, under the safe presumption that the researchers would do a more thorough job than the lay person. From the article, figure 2: > Mean spatial abundance of euphausiids per decade in the North Atlantic from 1958–2017 split into six time-periods 1958–1967; 1968–1977; 1978–1987; 1988–1997; 1998–2007; 2008–2017. https://www.nature.com/articles/s42003-021-02159-1/figures/2 https://www.nature.com/articles/s42003-021-02159-1/figures/2

xhkkffbf 5y ago

I realize that habitat loss is a big thing, but I also know that some krill-eating species like the big whales have rebounded over the last 60 years. Could this decline in krill be the result of the return of the whales?

jheitzeb 5y ago
Krill is a keystone species. Lose krill and the food chain collapses — at least krill is thought to hold such a role in the Southern Hemisphere. There, it is harvesting for omega 3 supplements that’s causing the decline. https://www.theguardian.com/environment/2008/mar/23/fishing.food https://www.theguardian.com/environment/2008/mar/23/fishing....
- eloff 5y ago
  I think mostly the krill is used as fish and animal feed as a source of protein. Supplements are probably a small part of the consumption. It seems like a bad idea to overfish the base food chain species. But then pretty much everything we do with the ocean is a bad idea. The only thing that has been positive where the oceans are concerned is creating marine reserves where commercial fishing is prohibited, and enforcing that.
aliasEli 5y ago
It seems pretty unlikely. For all whale specious the numbers are far lower than historical numbers. There is a huge amount of krill and there are a lot of other species that have been doing this for a very long time.

pvaldes 5y ago

> Krill lost 50% of their habitat in the last 60 years. Not necessarily. Krill species live from surface to fairly deep waters. Surface is an important, but small part on its entire habitat. We need to take in mind that all in this study is about the situation found when sampling an area between 0-10m deep. For Thysanoessa for example this means that if you don't find them at the surface there is still a 390m deep layer where they could still be located. Meganyctiphanes, Nematobranchion and Thysanopoda concentrate normally in waters below 400m by day (Saunders et al, 2013). They can migrate to surface [1] at night, but can also choose to remain close to the sea bottom in much deeper areas. It depends a lot on the species, location and time of the year. [1] More or less, surface does not mean 0m necessarily, can mean -15m or -20m also.