The decline of baleen whales has led to a decline of krill, researchers find | Hacker News Reader

The decline of baleen whales has led to a decline of krill, researchers find

news.stanford.edu

151 pointsgmays89 comments

So whales poop krill which feeds algae which feeds krill. Add in sunlight and saltwater microorganisms and I guess it’s possible that whales eating then shitting krill = even more krill. But like so many complex systems it’s hard to draw any conclusions. Whales are beautiful creatures and it would be great if the oceans were so full of them again!

In general, it's difficult for a process that takes krill as the only input to have more krill in the output than there were in the input. If whales cause a net increase in krill, it has to be through some other means than eating krill.

For example, wolves eating deer meant more deer (because losses to illness decrease when sick deer are caught and eaten before they can infect others).

OK, but that would seem to fall under "through some other means than eating the deer". If instead of eating sick deer the wolves exiled them, or vaccinated healthy deer, presumably you'd see the same increase in deer population.

That's too simplistic. The moment wolves start vaccinating healthy deer, there'll be a 20-30% anti-vax deer population.

Yeah, but then there's the impact of too many deer on the forests that they browse (assuming it's a species that's a browser rather than a grazer) - when there's overpopulation, they'll eat everything they can as they grow desperate through hunger.

A forest with all the seedlings eaten out struggles to recover from the death of mature trees, which is normally an opportunity for an explosion of growth - the decaying trunk restores nutrients to the soil, the sunlight streaming through gives the seedlings an opportunity to grow as fast as they can.

So continual overpopulation ultimately leads to the head of deer a given area of forest can support dropping significantly. Predation, whether by wolves or humans, can reduce the deer population to the extent that allows the forest to recover, which in turns leads to the forest being able to sustain larger populations of deer.

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.

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.

You're missing the phytoplankton bit - they need iron for photosynthesis, krill eat phytoplankton, whales eat krill, whales poop bioavailable iron.

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.

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

maybe krill reproduce faster when they’re under threat, like how WWII preceded the baby boom

(i am not a krill expert)

Oh, I have it! I have it! What if somebody would be fishing all this krill and sending it to floating factories to feed pets?

Your forgetting one more input… the sunlight. The intermediate step is the phytoplankton. The whale poop (the iron specifically) is a limiting factor that limits how much phytoplankton can photosynthesize.

It’s like fertilizing soil with the dead… it could in theory support ever growing populations.

Sunlight is a source of power; by assuming unlimited sunlight input we can rearrange as much material as we want, but we can't add or subtract any.

If we arrange more material into phytoplankton, that would seem to leave less material available to be krill.

> It’s like fertilizing soil with the dead… it could in theory support ever growing populations.

But this cannot work in theory. A population cannot grow if its only nutrient input comes from dead members.

> But this cannot work in theory. A population cannot grow if its only nutrient input comes from dead members.

That’s the point your missing. The nutrient input is coming first from the sunlight. The phytoplankton nutrient for the krill is limited by the available iron.

> Sunlight is a source of power; by assuming unlimited sunlight input we can rearrange as much material as we want, but we can't add or subtract any.

Photosynthesis creates nutrients at the base of all food webs (except deep sea geothermal vents) It’s able to allow plants to take carbon dioxide out of the air and fix it as a source of chemical energy. The sunlights radiative energy then is converted to chemical energy which then acts as a nutrient for other living things. The nutrient addition is literally arriving out of thin air. (C02 into sugars)

However, organisms and in this case the phytoplankton doing that photosynthesis, are limited by specific nutrients, otherwise known as regulating factors. [1] In this case sunlight, carbon dioxide, etc would allow for massive growth of phytoplankton in the ocean. However, even given unlimited amounts of those, the phytoplankton will hit a growth wall when it runs out of iron.

That iron, in this case, was locked up in vast amounts of krill. Krill from my knowledge can live up to 10 years. So that means that a balance will be reached between the krill and phytoplankton in terms of population densities and where that limiting nutrient of iron is stored.

Whales change that limiting nutrient balance. By eating the krill and releasing the iron, the phytoplankton is able to increase its growth rate.

Krill then, feeding on the phytoplankton blooms will reproduce quicker. Iron that was once locked up in krill for 10 years allows faster reproduction rates of new krill.

The energy input that allows both populations to grow in this scenario is the sunlight. Again, the iron is only a limiting factor. The limiting factor is not 100% of the energy input. The iron is not “used up” meaning it’s availability to allow increased photosynthesis remains.

The end result is that a significantly larger proportion of sunlight is captured and converted to living matter which allows a net positive gain in both populations. This is possible because the regulating factor for increased photosynthesis is maintained in the ocean at higher levels with whales.

1. https://en.wikipedia.org/wiki/Limiting_factor#Ecology

https://sciencing.com/effect-limiting-nutrient-ecosystem-517...

The process's starting inputs are sunlight and dissolved carbon dioxide that phytoplankton convert to biomass.

But a limiting factor is the trace minerals they need to do so - iron is key to photosynthesis. In fact, people have proposed deliberately seeding the ocean with iron to stimulate phytoplankton blooms to fix carbon dioxide... not sure I agree with that, given the risks of harmful algal blooms.

The krill eat the plankton, the whales eat the krill, the whale poop contains iron that the phytoplankton need, it's the great circle of life.

Are the krill sequestering more iron than they need? Assuming they aren't, then in this model processing by whales can lead to fatter krill (more biomass per unit of iron), but not more krill.

In most of biology, abundance of food would lead to more individuals as well.

You're talking about a fixed amount of iron. It can be in algae or it can be in krill.

But it can only be in one thing at a time. More algae can't lead to more krill if the existence of the larger krill population precludes the existence of the larger algae population.

Suppose I told you that by draining the iron from a bunch of humans we could promote the growth of iron-bearing plants that would feed a bunch of new humans. How much surplus iron could we drain from a living human? How many new humans could sustain themselves on that amount of iron?

But it's not necessarily true that both populations are limited by iron availability. These iron-hungry plants could be producing more, say, zinc than they themselves need, which could allow the human population to expand even with less iron available.

Give it a long time for coevolution to take place, then have something suddenly happen to the mosquito population that was extracting the iron from the people, and we could see the same dynamic.

> These iron-hungry plants could be producing more, say, zinc than they themselves need, which could allow the human population to expand even with less iron available.

There are a couple of ways this could work.

The human population might have access to a source of iron which is not available to the plants. In this case, we can model the system as iron going from a mine somewhere (say) to the plant population, mediated by human remains. The iron isn't being drawn from the human population.

Or, this human subspecies might store a lot more iron than it actually needs to survive. Maybe they grow their own metallic armor or something. In this case, the remains of one human contain enough iron to support several other humans, so returning human remains to the soil in order to grow more plants could cause in increase in the human population, though the new humans would have impaired armor or whatever.

The issue I see with the iron/algae/krill model is that it's explicit that the additional iron for the algae is coming out of the krill. So we have two questions:

(1) Can krill get their iron through some other means than eating it?

(2) Do krill sequester more iron than they need to survive?

I'm assuming that krill obtain their iron through their diet. So unless an adult krill sequesters more iron than it needs, it doesn't really matter how much algae the recycled iron can produce -- less iron in the krill population will necessarily mean a smaller krill population. If the krill population isn't limited by iron, it may be happy to grow to accommodate the new larger supply of algae. But in order to do that, it will need to keep a certain amount of iron. If that iron has to come out of the algae the new krill supposedly eat, then how much larger is the new supply of algae really? Once the krill population gets back up to its original size, all of the "additional" iron is gone.

Putting this another way, if we think that algae are limited by the availability of iron, and we also think that krill are limited by the availability of algae, then we aren't saying that krill are not limited by the availability of iron. They definitely are! But that limitation goes through the algae they depend on.

A theory I read is that when whales dive to the deep ocean they induce currents that bring iron to the upper layers. A sibling comment points out that iron is the bottleneck food for algae, so even a small amount of iron can create a huge mass of algae and krill as a consequence.

Just some quick Googling found this:

"Other types of whales, such as sperm whales, migrate to waters much deeper than the euphotic zone and they can scavenge iron from below and then return to the surface layer to defecate."¹

¹: https://theconversation.com/bottoms-up-how-whale-poop-helps-...

Wouldn't that mean we could also blame whales for occasionally causing red tides?

Not the main causes of course, I believe it is mine and fertilizer runoff which are the current leaders.

The likely reason is that when krill die by being eaten by whales, their remains are spread at the surface of the ocean, and algae can use the scarce elements that were sequestered in the krill bodies, allowing the cycle to continue.

When krill die due to old age, they might sink to the bottom and be buried in sediments, so the elements stored in their bodies will exit the cycle, causing reduced biomass in the cycle, and this loss will not be completely compensated by what river water brings from the erosion of the continents.

That makes some sense. Thank you.

Sunlight and iron are also inputs. Sunlight from the sky, obviously, and iron from transported sediment.

A system that uses either more efficiently could result in a net increase in biomass, even if the system is “processing” more krill per unit time while doing so.

I understand the limiting factor is iron, which the plankton require.

This can be blown in from the Sahara occasionally. The whale faeces float, whales eat at depth but due to the high pressure of the deep ocean they can only defaecate at the surface.

If they’re in an eddy and grouped as a pod the nutrients are concentrated in an area the plankton can then use the iron, and the krill which live for six years or so feed on it.

The idea being to seed the oceans with simulated whale faeces this should jump start the plankton and ideally the krill giving the whales an opportunity to feed should their numbers expand, a trial in the Arabian ocean is planned to start.

Currently iron levels are only sufficient near the coasts, the hope being that all far more of the oceans could start to support life instead of being deserts.

This Inside Science podcast has a good bit about it all:

https://www.bbc.co.uk/programmes/m00114n7

Just thinking about it, this sounds slightly like Dune. The whales being the sand worm of the oceans, reprocessing krill into plankton food which is thought to have a huge effect in sequestering carbon.

It sounds like what's happening is the whales are working as a sort of churn, cycling material from deeper in the water up to the surface where plankton can metabolize it.

Isn't whale poop also known as "ambergris", a very valuable commodity used in perfume manufacture?

I wonder how much of this recycled krill nutrient is removed by humans in the form of ambergris, to meet the requirements of wealthy women.

[Edit] Apparently it is excreted, perhaps by pooping; but it isn't quite poop.

https://en.wikipedia.org/wiki/Ambergris

Ambergris comes from sperm whales, a toothed whale that mainly eats squid, not krill.

I would suggest an alternative possibility.

Whales eat squids.

And ships are made of iron.

Humans are probably putting more iron in the sea than whales do.

A different type of whale eat squid. The baleen combs of baleen whales is unsuited for chewing squidy bits.

Rusty ships are avoided, some of the iron is molecularly bonded to other metals and minerals, and rust from ships will sink immediately, and isn't really very bio available anyway. Rust flakes and particles are kinda difficult (and large) for crustaceans to rend and digest.

Irony whale poop has buoyancy, and the iron is bio available.

What about fortified breakfast cereals? Could we just scatter a boatload of Captain Crunch instead?

100% correct. May I introduce squid floating larvae in this equation?

And squid eat...

The plural of "squid" is "squid", as the plural of "sheep" is "sheep".

Perhaps "squids" refers to multiple superconducting quantum interference devices.

</pedantry>

While I’m sure you are not eating whales, you may be consuming some resources that consecutively affect whales population, so it’s might not be as easy as it sounds.

This might seem counterintuitive but it’s not really a new concept in ecology. For example it is well-understood how hippos contribute to biomass in African rivers despite being ravenous consumers. As with the whales hypothesis, it’s from their poop.

It’s not that crazy a concept that increasing consumers can increase biomass. We all learned about scavengers and decay—life that consumes life, but in doing so, frees nutrients for other life. By short-cutting between the end of a complex life, and the beginning of a simple life, such creatures contribute to the overall efficiency with which the ecosystem captures solar energy and applies it to arrange environmental chemicals into living things.

The difference between a predator and a scavenger is just timing. If anything, predators take an even shorter cut between the end of a life (they cause it) and the availability of nutrients via digestion.

And as a gut check, things must work this way in general because the earth started with simple producers (photosynthesis or something like it), and consumers came later. Yet the overall biomass increased over time since then, even as consumers increased.

The same with scything meadows. Apparently if you let a meadow uncut, the plant/biodiversity rapidly declines.

Anecdotally I've found this to be true, my grandparents had mountain meadows that they didn't harvest for tens of years and indeed, the hay there seems to be almost "monocrop" compared to the ones that are harvested.

I wonder if our own species would be improved by the return of predators, say one t-rex or sabertooth per every x population. The population control would reduce our carbon footprint. Spending on chronic medical conditions that make people slower would be reduced. There would be more incentive to exercise, less lassitude and boredom. Increased violent sudden death could be considered a drawback, but look at the big picture.

That’s ridiculous. In parts of India and Africa, people live among tigers and they fend themselves off just fine. In rural America we have bears and we fend them off. Sure cities lack those predators, but cars make up for that.

You just want more Covid, but I bet you don’t actually want more covid.

Could we release a couple of tigers in your house for the greater good, or would they mainly inhabit places with higher contentrations of paupers and other such undesirables?

I doubt that at this point of our technological advance any predator could really pose such a threat to humanity in whole. No PETA in the world would save such predator from extinction, and this would come not from everyday Joe who started to excercise more, but from military and police (and maybe some other organizations, depends on real threat level)

The most effective predators of humans are other humans. And in places where such predation happens regularly, e.g. countries with long lasting wars, there is indeed a lot less trouble with chronic medical issues, but there is no evidence that the species is improved. By all reasonable measures it is in fact a massive detriment to improvement of any kind.

Our most reliable and proven form of population control is the education of girls. If we truly care about saving the species this is the most effective route available to us in the next generations along with ending the use of non-renewal energy

Impactful funds you can support: https://impactful.ninja/best-charities-for-female-education/

Exactly, this is so well documented, if anyone's still scared of a Malthusian disaster, focus on overcoming cultural biases against educating girls.

I would say that war, famine, and disease are our most proven. Education of women is speculative, as it has not been a factor in the past like the first 3, and used often as a hand wavy way for people who are smart enough to understand the math to say they are against population control.

If we want to solve a problem, we should try to choose the solutions that don't involve killing people :-)

All trends show that the countries with low levels of poverty, high levels of education and women equality results in fewer births.

Women are able to have careers and want to finish their education and get work experience before they think of children. In countries like Scandinavia, the average age of first time mothers are increasing year by year. We also see that cities within the country with a lot of highly educated jobs have a higher age than others

I'm will absolutely concede that it may work and we should try anyway. But correlation != causality.

> correlation != causality

That's also an argument against your point about war, disease, and famine.

When you put a sword through someone, causality is not in doubt.

> If we want to solve a problem, we should try to choose the solutions that don't involve killing people :-)

The anti-natalism movement has it right IMHO. If we voluntarily limit birth to far less than replacement, overpopulation would correct itself in as little as a generation. But we won't do that, we're not wired that way. Instead, we'll keep chugging along past the carrying capacity of the biosphere and Gaia will correct our population for us, abruptly.

I'm not trying to be snarky - but take moment to google "population control education"

Those three are all proven - to not work in the long term! War, famine,and disease tend to be followed by increased reproduction. A combination of sadism and intuitiveness are the only "advantages" of the four "proven" appoaches of the horsemen and arrogant know-nothing social darwinists.

Education of women is linked to a more K-Stategy approach among many other reasons on a personal level (ambitions to a higher purpose, learning in detail all of the cringe inducing ways an already known to be painful birth can go wrong for you and your children). K-strategy is all about quality over quantity which is what we actually want and need anyway. While a largely uneducated nation may say export the most logs with a large uneducated populace with handtools as lumberjacks - what they need from the transaction is money and lumber is better. And from there to furniture and a more advanced industrial economy.

Well that's a really good point!

> Our most reliable and proven form of population control is...

limited resources.

Education has got nothing on starvation.

Thank you, Jonathan Swift

Too unethical and non-humanitarian. We already have a smaller scale reduction of "spending on chronic medical conditions" -- COVID-19. No one considers it's "a drawback, but look at the big picture".

This would lead to more gun ownership.

> The population control would reduce our carbon footprint

Most of the carbon footprint comes from a small portion of the population. The kind of people who could afford to pay for defence against the predators.

I think it would be difficult to implement your suggestion without having an effectively eco-fascist outcome.

> Through eating krill and then defecating, whales release iron locked within krill back into the water, making that iron available to phytoplankton, which need it to survive.

So sounds like removing the whales has removed iron from the system permanently and it can't recover then.

Seeding the ocean with iron had previously been suggested for carbon sequestration as well https://edu.rsc.org/feature/iron-ocean-seeding/2020176.artic...

I believe the numbers work out to sequestering 1/3rd of CO2 output for around $4 billion per year and creating hundreds of billion in fish as well as untold benefits for the ecosystem

Canadian tribes have tried it https://www.q13fox.com/news/canadian-tribes-ocean-fertilizat...

Would having more whales boost CO2 sequestration, or just increase the ammount tied up in the oceans at any given time?

If the former, gradual seeding could leave a persistent effect behind in the form of increased whale populations. Seeding wouldn't just be a one-time exchange of money for CO2 sequestration.

Doesn't carbon get sequestered on the ocean floor quite a bit? I imagine more in the ocean would mean more getting trapped in the ocean floor.

limestone is the largest carbon reservoir in the world, storing about 80% of all the world's carbon, and nearly all limestone is former marine organisms.

organisms like krill that now have difficulty accreting carbonate structure and surviving due to the increased co2 acidity of the oceans :D

There are always several cycles going simultaneously in ecology, nothing is permanent.

Extinction is permanent.

There are also lots of spirals like this that lead to rapid population collapse.

The thing that scares people about climate change is that we don't know when humans will be caught in one of those collapses, but we know that it will happen eventually. There are lots and lots of species that we need to sustain billions of humans.

> Extinction is permanent.

You never get quite the same thing but convergent evolution can mean extinction isn’t 100% permanent given enough time.

badgers vs kiwis you mean.

key words "given enough time"

New species also sometimes need an empty niche to evolve. It's pretty tyrannical of us humans to decide that the species that exist now are the ones that get to inhabit that niche forever.

all of humanity stands on the bedrock of a diverse and complex ecosystem. what's tyrannical is the set of people and institutions that unaccountably insist it's their right to go around systematically poking out thousands of fresh empty niches under the world's collective feet

you're not actually concerned about the space available for new species. you're not even concerned with the species we have now. if you were concerned about species diversity, you would be concerned that we are way below replacement rates. you can't spin a mass extinction as some kind of victory for the liberty of nature.

If all these ecosystems are so fragile, then it's our responsibility as a species to re-engineer them to be more robust.

if you want to have that conversation, you must agree it would be irresponsible to destroy the single extant system by applying large uncontrolled inputs, before such an engineering technique is understood. we are currently shitting where we eat.

Do you sincerely believe that humans can re-engineer ecosystems to improve upon hundreds of millions of years of evolution?

We don't even understand any single organism or any ecosystem completely.

Biodiversity recovers at some rate, and we destroy it at some rate.

At present, the magnitude of those rates is 100k to 1.

That’s clearly an unsustainable situation.

The greatest increases in species diversity have generally occurred after extreme destruction. Early cyanobacteria killed nearly all life on earth by consuming all available iron and polluting the entire planet with toxic oxygen.

sorry, we have no time to wait it happen, and even expect it will recovery is not practical. do you want to wait at least one million for it? is human still exists that times? human changed world in very short time, there are no time for evolution

Species aren’t permanent.

They’re also not static.

Discussed yesterday, 64 comments:

https://news.ycombinator.com/item?id=29101594

Aren’t baleen whale populations rapidly recovering though? Humpback whales more so but blue whales also improving. Will krill populations return or does iron need to be added back to the ocean to return both krill and whale populations back to where they were?

Krill has become an important commercial product, which means we have the risk that humans end up harvesting so much krill that the whales starve.

https://en.wikipedia.org/wiki/Krill_fishery

Tangentially related... Large animals store considerable amount of carbon.

> if we restored global whale populations to pre-whaling levels, they'd sequester 1.7 billion tons of carbon/year.

https://twitter.com/lauraetam/status/1453054149583462405?fbc...

Here’s a Nature paper on it:

https://www.nature.com/articles/s41586-021-03991-5

> ...which uses sound waves at several different frequencies to measure how much prey is around.

Cool use case for echolocation.

Sonars are bad for whales and other cetaceans.

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