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Not necessarily. It's not immediately intuitive is all. For example, maybe krill do a poor job recovering nutrients from dead krill, while they do great job of

Not necessarily. It's not immediately intuitive is all. For example, maybe krill do a poor job recovering nutrients from dead krill, while they do great job of it with whale waste. In this case, whales would keep the overall amount of nutrients available to krill high while also consuming them. Who knows what's actually going on here, but it's really not difficult for these sorts of highly interrelated systems to end up with counterintuitive dynamics.

choeger 5y ago
Logically, it cannot work via pre-existing nutrients alone. Even if wales poop out 100% of the relevant chemicals they ingest from krill again, because they do not need it, krill won't be able to eat it completely as it is diluted in the sea. There's always losses. So someone has to produce something. For instance: Krill need chemical X when young but create it when older in large quantities. Wales poop out X then. Or wales create X, while krill do not.
- EdwardDiego 5y ago
  You're missing the phytoplankton bit - they need iron for photosynthesis, krill eat phytoplankton, whales eat krill, whales poop bioavailable iron.
- Retric 5y ago
  The limitation is on biomass not numbers of krill. Replacing a X million with average weight 2g with a population that weighs 1.8g and numbers could increase even if biomass decreased. But even that’s assuming a uniform static population. Suppose in area X there is an abundance of Krill and iron, but in area Y they are heavily limited. Whales migrating through Y might cause a net migration of iron from X to Y even if they aren’t 100% efficient. Another possibility is recycling. Suppose the rate of iron addition via dust seeding is A tons per day, the rate of iron lost when a krill dies of old age is 60% and the rate of iron lost when a krill is eaten by a whale is only 30%. If the average age of krill dropped by say 20% then the biomass of krill should significantly increase.
EdwardDiego 5y ago
Whale poop liberates nutrients locked up in krill that phytoplankton need - (the article mentions iron, a trace element essential for photosynthesis). Phytoplankton convert sunlight and dissolved CO2 into biomass, krill eat phytoplankton, baleen whales eat krill. So the role of the whale poop is fertilisation. https://en.wikipedia.org/wiki/Iron_fertilization https://en.wikipedia.org/wiki/Iron_fertilization

choeger 5y ago

Logically, it cannot work via pre-existing nutrients alone. Even if wales poop out 100% of the relevant chemicals they ingest from krill again, because they do not need it, krill won't be able to eat it completely as it is diluted in the sea. There's always losses. So someone has to produce something. For instance: Krill need chemical X when young but create it when older in large quantities. Wales poop out X then. Or wales create X, while krill do not.

EdwardDiego 5y ago
You're missing the phytoplankton bit - they need iron for photosynthesis, krill eat phytoplankton, whales eat krill, whales poop bioavailable iron.
Retric 5y ago
The limitation is on biomass not numbers of krill. Replacing a X million with average weight 2g with a population that weighs 1.8g and numbers could increase even if biomass decreased. But even that’s assuming a uniform static population. Suppose in area X there is an abundance of Krill and iron, but in area Y they are heavily limited. Whales migrating through Y might cause a net migration of iron from X to Y even if they aren’t 100% efficient. Another possibility is recycling. Suppose the rate of iron addition via dust seeding is A tons per day, the rate of iron lost when a krill dies of old age is 60% and the rate of iron lost when a krill is eaten by a whale is only 30%. If the average age of krill dropped by say 20% then the biomass of krill should significantly increase.

EdwardDiego 5y ago

Whale poop liberates nutrients locked up in krill that phytoplankton need - (the article mentions iron, a trace element essential for photosynthesis). Phytoplankton convert sunlight and dissolved CO2 into biomass, krill eat phytoplankton, baleen whales eat krill. So the role of the whale poop is fertilisation. https://en.wikipedia.org/wiki/Iron_fertilization https://en.wikipedia.org/wiki/Iron_fertilization