The Phytoplankton Are Starving

The reduction in phytoplankton is not due to oceanic warming, but instead to overfishing. Guest writer Ed Caryl digs into the subject of phytoplankton.

Phytoplankton clouds shown in light green. Source: NASA

The Phytoplankton Are Starving
By Ed Caryl

A recent press release from Dalhousie University, Nova Scotia, announced an article published in Nature (behind a pay-wall) that we’ve been losing 1% of our phytoplankton each year dating back to 1899, meaning 40% since 1950. The article blames it on ocean warming. The article was discussed in July on WUWT and here. Let’s pull our heads back a bit more and look beyond warming.

Why are phytoplankton important?

Phytoplankton or algae are single-celled, photosynthesizing creatures at the “bottom” of the ocean food chain. They take in sunlight and CO2 and produce carbohydrates, just like plants do on land. They are the source of the biomass that all larger animals and fish feed upon. Without them, life in the ocean would not exist. Yet, much of the literature makes no mention of any dependence in the other direction, i.e. phytoplankton depend on the creatures higher up in the food chain.

Phytoplankton are a hybrid of plant and animal. Some have locomotion capability as if they were single-celled animals. They need the same nutrients as all plants: CO2, nitrogen (as nitrates or ammonia), and phosphorus (as phosphate); iron, zinc and manganese are also needed in trace quantities. When there is an excess of these nutrients, such as in agricultural runoff, “blooms” can occur where runaway reproduction produces so many that during the night when they are not photosynthesizing they can consume all the dissolved oxygen in the water, and thus suffocate themselves and the fish.

Why are phytoplankton disappearing in deep ocean areas?

In the deep ocean, away from nutrient-feeding rivers and streams, the phytoplankton population is generally low. This can be seen in the graphic above from satellite data where blue indicates low chlorophyll.

Upwelling from the deep-ocean delivers nutrients from the bottom and increases the population in areas close to shore where waters are shallow, and where rivers and streams bring nutrients from land. The phytoplankton population seems to have increased in shore areas in recent years, probably due to nutrient runoff from agriculture, while the mid-ocean gyres are still seeing population decreases.

The questions then are:

1) Why is the mid-ocean so generally poor in phytoplankton?
2) Why has the overall phytoplankton population dropped?

Let’s discuss the possibilities: Is increasing CO2 in the atmosphere causing it?
This is unlikely for three reasons. First, CO2 started increasing in a significant way many years after the reduction in phytoplankton started. Second, CO2 is a nutrient that should stimulate growth, not inhibit it. Three, the recent inshore population increase seems to go against the CO2 influence.

Is ocean warming the culprit?

Note that planktons are plentiful in very warm equatorial waters where nutrients are available. Even though the far north and south seem to have more phytoplankton, warm temperatures do not seem to be the limiting factor. Phytoplankton are not a single monolithic species. There are thousands of species of phytoplankton, adapted to various environments, including temperature.  Some phytoplankton also diurnally move vertically in the water column through large temperature gradients.

So, what could be limiting phytoplankton? The likely culprit is the limitation of nutrients. Phytoplanktons are starving in the mid-ocean. Why?

The oceans are mostly a closed ecosystem. Inputs to the system are sunlight and nutrients from rivers and streams. 95% of the biomass in the ocean is phytoplankton. Everything else in the ocean depends directly or indirectly on phytoplankton. Zooplankton: copepods, krill, and shrimp eat phytoplankton. Small fish, such as herring, sardines, and menhaden eat the zooplankton. Large fish eat the small fish. At the top of the food chain are: squid, tuna, salmon, sharks, whales, porpoise, etc…and finally us humans. But remember, this is a closed system. Except for what man removes, everything else recycles in the ocean. Everything in the ocean lives, excretes, dies, or is eaten by something. Even if it falls to the bottom, bacteria, worms, and crabs consume what is left. Only the non-digestible mineral skeletons and exoskeletons remain in the ocean-bottom sediments. Except for what man removes, the nutrients remain in the ocean. And when man does remove those nutrients, it’s forever.

Man’s removal from the oceans

The problem is that we have fished out the oceans. Only 10% of the large fish found in the oceans in 1950 remain. And we have been over-fishing the oceans far longer than just the last 60 years. Even backe in 1950, people were already noticing a reduction in stocks of whales, salmon, cod, halibut, and other fish. We probably have less than 10% of the large fish and whale stocks that were present before we began harvesting the seas in earnest.

Where does the nitrogen that phytoplankton require come from? At the the mid-ocean levels, some comes from nitrogen fixing bacteria, but the rest comes from excrement in the form of urea and ammonia from bacteria breaking down protein as carcasses decompose. Iron, molybdenum, and phosphates come from the same sources. But remember we are removing large amounts of fish protein from the ocean, especially whale, tuna, shark, and other large fish. 90% of what was there is now gone. We are removing more every year. The fish products are no longer available to the phytoplanktons. Their food supply has diminsihed. They are starving.

What does that mean for the carbon cycle?

Why is this important? If we have lost 40% of our phytoplanktons, then we have lost a significant part of the photosynthetic biosphere. Photosynthesis binds 100 to 115 million metric tons of carbon each year. Phytoplanktons are responsible for half the photosynthesis that occurs on the planet. If we have lost 40% of the phytoplanktons, then we have lost 20% of our total photosynthesis capability, or the conversion of more than 20 million metric tons of carbon per year, in carbon dioxide, into oxygen and water. This is a huge loss, but it pales in comparison to a larger loss.

Phytoplanktons have silica and calcium carbonate skeletons. Phytoplanktons are eaten by copepods and other zooplankton, which also have calcium carbonate skeletons and exoskeletons. 40% of the carbon is converted into calcium-carbonate shells and excreta that sink to the bottom, and 60% to dissolved organic carbon originating from flesh. In 1950 planktons were sequestering 16.6 billion metric tons of carbon. Today, planktons convert 10 billion metric tons of carbon. If we have lost 40% of the phytoplanktons since 1950, i.e. 40% of the carbon sequestration capability, then 6.6 billion metric tons of carbon should appear in the atmosphere.

Currently we are adding more than 5.5 billion tons of carbon yearly to the atmosphere from fossil fuel and cement production (here). In 1950, we were adding more than 1.5 billion tons of carbon per year. That’s a 4 billion ton increase. Four billion tons a year is the yearly average atmospheric carbon-in-CO2 increase. But if in that same period, 40% of plankton have starved out, they are no longer sequestering 6.6 billion tons of carbon. These figures don’t agree. This is probably because the plankton loss is not quite 40%, but somewhat below 30%. Still, the plankton loss alone can account for the rising atmospheric CO2 levels.

Maybe it’s time we curtailed eating fish for a while, and focus on consuming poultry, pork or beef.

27 responses to “The Phytoplankton Are Starving”

  1. DirkH

    I was thinking along the same lines; you harvest fish, you remove nutrients from the oceans. Maybe we should bring in a petition at

    http://www.change.org/petitions

    that everyone who removes a ton of fish from the open ocean must drop an equivalent amount of nutrients in return. Ordinary fertilizer would do. It’s funny how the leftists are protesting against ocean seeding experiments; when what we do day in day out is the exact opposite of seeding.

    1. Ed Caryl

      Good idea. And a great ending point!

  2. R. de Haan

    I think are on thin ice with this article and I question both claims. Why?
    At WUWT the scientific method estimating the loss/count of phytoplankton was questioned. Besides that we know for fact that water temperature does not affect the pytoplankton bloom but the availability of nutrients.

    So I have big trouble accepting the loss of plankton for fact.

    In regard to the claim of overfishing and fishing methods (by other reports), which is a serious problem in several places, we see the gap of lost volume filled up with other species very quickly.

    We know for example that tuna eat jelly fish and in those waters where the tuna numbers have been reduced the numbers of jelly fish have exploded, compensating for the “loss of mass”.

    So one species is quickly replaced by another.

    In regard to the availability of nutrients that produce algae and plankton.

    I remember that the ban of phosphates in washing powders in the Seventies caused a drop of the fish stocks in the North Sea, simply because less plankton was produced. The use of fertilizers in agriculture on the other hand, washed out from the land into the rivers and into the oceans on the other hand increase the growth of phytoplankton.

    We also know that fish populations adapt to “fishing stress” and produce more off spring.

    So I think we need to do more research by independent scientist because Global Warming and overfishing are subject to serious exploitation by alarmists and the UN in order to gain Global Control over our oceans.

    Besides that, you only have to look at the Space observations from NASA to see there isn’t much to worry about:
    http://earthobservatory.nasa.gov/Search/index.php?cx=002358070019171462865%3Arvzidec6wz4&cof=FORID%3A11&q=Phyto+plackton+bloom

    I will do some desk research on the subject and post my findings but at this moment in time dismiss both claims.

    Reply: You’re welcome to post any findings here as a guest writer. I’d be more than happy to do it. Contact me by e-mail if you’re interested. I agree with your statement that research needs to be done by independent scientists. Right now there’s clearly an agenda driving the science in a particular direction. – PG

    1. Ed Caryl

      Yes, overfishing changes the prey/predator relationships. Removing tuna will favor sea jellies. But what do sea jellies eat? Plankton.

    2. DirkH

      Consider the huge variation between algae booms near river deltas and the oceanic deserts in the Pacific. These deserts are vast; and i don’t know about the distribution of high sea trawlers; but i would expect fishing fleets to go everywhere where they can find fish, so probably they constantly increase the nutrient depletion along the edges of the ocean deserts.

  3. JohnWho

    ” Still, the plankton loss alone can account for the rising atmospheric CO2 levels.”

    But…, but…

    Oh, nevermind!

    Someone will point out that the problem is still man-made and we need to stop polluting our skies with CO2.

    1. Ed Caryl

      I predicted that reaction (to my wife), even quoted you in advance.  Keep thinking.

      1. JohnWho

        Hey, no fair quoting people before they make their statement!

        LOL

        On the other hand, by my saying that “someone” would say it, and then saying it, perhaps I’ve self-fulfilled my prediction?

        The plants on my lanai seem to be enjoying all of this increased CO2 in the air – so what’s the fuss? Well, unless they hear that the CO2 that man has put into the air is a pollutant. I’m not sure what they will do then.

  4. Alondra Ecosystem

    It should not be inhaled as in extremes this could lead to asphyxiation. Alondra Ecosystem

  5. snorbert Zangox

    Before EPA went wild, we were dumping sewage sludge solids into the ocean off the coasts of New Jersey and New York. Those solids contained all of the nutrients of which you spoke. Perhaps our old ways, although they offended our sensibilities (I know of no other reason for the ban), were better than our new ways.

  6. mitchel44

    We must be an anomaly here, lobster is doing OK. “The largest landings , by a wide margin come from LFA 34 in SWNS. Landings there rose dramatically from 1990 to 2000/01 but have been slowly declining in recent years. They still remain well above historic landings.” http://www.gov.ns.ca/fish/marine/sectors/invert.shtml

  7. Willis Eschenbach

    First, let me say this is a clear, understandable and well written article. However, it says:

    Man’s removal from the oceans

    The problem is that we have fished out the oceans. Only 10% of the large fish found in the oceans in 1950 remain. And we have been over-fishing the oceans far longer than just the last 60 years. Even backe in 1950, people were already noticing a reduction in stocks of whales, salmon, cod, halibut, and other fish. We probably have less than 10% of the large fish and whale stocks that were present before we began harvesting the seas in earnest.

    Where does the nitrogen that phytoplankton require come from? At the the mid-ocean levels, some comes from nitrogen fixing bacteria, but the rest comes from excrement in the form of urea and ammonia from bacteria breaking down protein as carcasses decompose. Iron, molybdenum, and phosphates come from the same sources. But remember we are removing large amounts of fish protein from the ocean, especially whale, tuna, shark, and other large fish. 90% of what was there is now gone. We are removing more every year. The fish products are no longer available to the phytoplanktons. Their food supply has diminsihed. They are starving.

    Right now, the food chain in the ocean goes something like this:

    Phytoplankton –> Herbivorous zooplankton –> Carnivorous zooplankton –> Carnivorous small fish –> Carnivorous big fish (tunas, etc.)

    Now, basically nobody in this whole list of eaters and eaten creates anything, except the phytoplankton. Everyone else either eats the phytoplankton, or eats someone who eats the phytoplankton, and on down the line.

    Humana catch and remove about 70 million tonnes of mostly big fish from the ocean annually. But the amount of mass at each trophic level reduces by about 90%. Tuna are four trophic level up from phytoplankton. This means that for every kilo (pound) of fish that we eat, there are about 10,000 kilos (pounds) of phytoplankton that are supporting that fish.

    That means that we are removing something on the order of one ten-thousandth (0.01%) of the nutrients that the phytoplankton that fed those tuna depend on …

    However, that’s not all. Much of the phytoplankton goes to feed things that are generally not eaten by humans. As a result, the reduction in phytoplankton nutrients is even smaller than 0.01%. Much of it is never seen by humans in any form.

    As a result, your hypothesis (reduction in plankton results from human usage of the required nutrients) fails by a number of orders of magnitude. We simply don’t remove enough nutrients to make a difference.

    1. DirkH

      I don’t think it works that way. Many of the critical nutrients – phosphates, iron, nitrates – are concentrated in organisms higher up the food chain. I’m not a biologist so i can’t quantify it but removing a ton of tuna removes much more iron from availability than removing a ton of phytoplankton i would think.

      Your argument in its pure form would only hold if we removed phytoplankton instead of fish.

      You say, 0.01 % – per year, that is, if i understand correctly. Now imagine a nutrient concentration factor of 100; that brings it up to 1 % a year. Suddenly the cumulative effect of years of fishing looks much more dramatic.

      Could this not make a difference?

      1. Ed Caryl

        Thank you Dirk, for pointing that out. I really didn’t want to get into that argument with Willis on my own. I respect and admire Willis Eschenbach a great deal, but in this case he needs to think about it some more.

      2. Willis Eschenbach

        Dirk, you say:

        I don’t think it works that way. Many of the critical nutrients – phosphates, iron, nitrates – are concentrated in organisms higher up the food chain. I’m not a biologist so i can’t quantify it but removing a ton of tuna removes much more iron from availability than removing a ton of phytoplankton i would think.

        Your argument in its pure form would only hold if we removed phytoplankton instead of fish.

        You say, 0.01 % – per year, that is, if i understand correctly. Now imagine a nutrient concentration factor of 100; that brings it up to 1 % a year. Suddenly the cumulative effect of years of fishing looks much more dramatic.

        I doubt that, I’d have to see a citation. Why should a small fish require less iron or phosphate (per kg) than a big fish? Yes, pollutants are concentrated as we move up the food chain. But phosphorus or iron? Sorry, but I’d have to see some hard numbers to believe that. That’s as unbelievable as Ed’s claim that “For nutrients like iron, the sea is a closed system, and what man takes out is never returned.” Nonsense. Much of what is taken from the sea returns to the sea, as runoff from the land.

        And Ed, you give a link to an article saying that the iron in whale poop is vital to the ocean … but where did that iron in the whale poop come from? Not from the whale, that’s for sure, it’s not manufacturing iron. So it must come from … wait for it … the phytoplankton. As the article says:

        The team confirmed the iron came from krill by analysing the iron content in whole krill and sampling genetic material from the whale faeces for krill DNA. “We confirmed the vast majority of the iron in the poo came from krill,” says Nicol.

        And because of that, human predation on whales makes no significant difference to the amount of iron in the ocean.

        Finally, you guys have a vastly exaggerated idea of how much material humans remove from the ocean. Yes, we take out some 70 million tonnes of marine organisms per year … but total fish biomass (not plankton, but fish) is on the order of 2,000 million tonnes. That means total plankton biomass is several orders of magnitude larger than that.

        Which in turn means that, even if we use a “nutritive concentration factor” of 100 as Dirk suggests, we’re still orders of magnitude too small to be starving the phytoplankton to death by taking their nutrients.

    2. Ed Caryl

      Willis,
      I note your comment. But as DirkH points out, the critical nutrients, especially iron, get concentrated as they pass up the chain. There is an article here:
      http://www.newscientist.com/article/dn18807-whale-poop-is-vital-to-oceans-carbon-cycle.html
      that describes how the iron normally gets returned to the sea, and what our predation on whales has done. Also remember that for baleen whales, there are only two trophic steps: phytoplankton -> krill -> whales. For nutrients like iron, the sea is a closed system, and what man takes out is never returned.

  8. R. de Haan

    Where can I find your e-mail address?
    Reply: See the side bar, under “Contact”. -PG

  9. Willis Eschenbach

    Ed Caryl
    25. August 2010 at 19:09 | Permalink | Reply

    Willis,
    I note your comment. But as DirkH points out, the critical nutrients, especially iron, get concentrated as they pass up the chain.

    Ed, thanks for the reply. I asked for a citation that big fish have more iron per kg than small fish. Until that arrives, your repetition of his claim doesn’t advance our knowledge. Nor does the claim you cited, viz:

    For example, your citation says:

    Using estimates of the whale population before commercial whaling in the Southern Ocean began early last century, Nicol predicts that baleen whales – now endangered – once consumed about 190 million tonnes of krill every year and produced 7600 tonnes of iron-rich faeces.

    Larger populations of whales would have produced more of this “bio-available” iron, leading to bigger phytoplankton and krill populations in turn, says Nicol.

    Since the iron in the whale feces is from krill, and was “bio-available” when the whale ate it, the presence of the whales has not added a single atom of iron to the ocean.

    I await the citation that shows that big fish have more iron per kg than small fish …

    w.

    1. DirkH

      Willis has a point.
      Here’s a list with a lot of fish species and their iron content:
      http://www.ferralet90.com/Patient_Information/About_Iron/Dietary/Foods/Fish-Shellfish.aspx

      No systematic i recognize…

  10. Willis Eschenbach

    DirkH
    27. August 2010 at 18:21

    Willis has a point.
    Here’s a list with a lot of fish species and their iron content:
    http://www.ferralet90.com/Patient_Information/About_Iron/Dietary/Foods/Fish-Shellfish.aspx

    No systematic i recognize…

    Thanks, Dirk. The fish on the list with the highest iron content is the Atlantic Sardine … which is way, way down on the food chain. It is a filter feeder eating plankton.

    So I think we can toss the “iron gets concentrated up the food chain” claim in the trash. Herring, another filter feeder that eats only plankton, has as much iron as tuna, which is at the very top of the food chain.

    I stand by my conclusion. The amount of nutrients removed from the ocean is trivial compared to the size of the plankton biomass.

    w.

  11. Ed Caryl

    Willis,
    Then why is the phytoplankton biomass shrinking?

  12. Willis Eschenbach

    Ed Caryl
    27. August 2010 at 23:58

    Willis,
    Then why is the phytoplankton biomass shrinking?

    Excellent question, Ed. The paper claims that phytoplankton biomass has shrunk by 50% over the last century, and 40% over the last 50 years.

    Phytoplankton is the foundation of the ocean. Everyone else is just along for the ride. As a result, if the phytoplankon had truly been cut in half, so would the numbers of every other living being in the ocean, from zooplankton to whales and jellyfish.

    So my answer would be, we don’t know a) if the phytoplankton biomass is shrinking, and b) how much it is shrinking.

    Not knowing either of those, it is way, way too soon to say why it might be shrinking.

    w.

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  14. Tom Ward

    Hi, I’m currently doing AS level Biology and I’m doing a project on the Reduction of Phytoplankton in the oceans.

    I was wondering if anyone could give me three practical solutions that could be done globally which would slow down the reduction in their numbers.

    Thanks, Tom

  15. William Burgess Leavenworth

    We’re just getting into the phytoplankton component of the Gulf of Maine, here at the Gulf of Maine cod project. However, the menhaden and bivalves that once kept phytoplankton grazed down are nearly gone. Hundreds of millions of menhaden once made seasonal journeys along the New England shore (check the MA pound net and weir returns for the last quarter of the 19th century, and compare them with today’s menhaden catch and the catches reported before the Civil War). Additionally, there were filter-feeding bivalves in every estuary and on every New England fishing ground long since trawled to oblivion. Baleen whales are at a fraction of their original numbers in the NW Atlantic; the Atlantic grey whale is extinct. So, can someone tell me what happens when there are very few phytoplankton grazers other than zooplankton, and few zooplankton predators? The Gulf of Maine contains barely 5% of the vertebrate biota it contained in the 19th century.

  16. William Burgess Leavenworth

    Hasn’t someone recently published a paper showing that diatoms in pelagic waters can survive with less iron than diatoms in estuarine waters? Wouldn’t that make some difference in the amount of iron available to pelagic and estuarine predators? Did foragers once crowd inshore seasonally to get better iron forage through clupeid planktivores that spawned inshore? All of the work we’ve done with coastal weir catches in the late 19th century suggests that pelagic predators crowded inshore when clupeids came inshore to spawn and then feed.