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A K-Brief (aka. Knowledge Brief) is a series of visual models, each with an explanation that ties them together into a cohesive story that as briefly as possible explains what experts need to know to be able to contribute their knowledge to improve the K-Brief.


How do we stop the collapse of our ocean food chain (web)?

LAST EDITED:  2024-05-21 13:36

ABSTRACT:  While Net Zero CO2 Emissions will certainly help avoid future acceleration of the collapse of our ocean food chain, it is clear that our ocean food chain has been declining for many reasons other than global warming and CO2 increases; so, achieving Net Zero CO2 Emissions alone will not be sufficient to save our ocean food chain (web) from collapse. And even if we fail to reach Net Zero and/or even if global warming continues, we desperately need to find a reliable way to prevent the collapse of the ocean food chain!

LEAD:  Brian Kennedy and the TCC Team

Problem Description

If that decline continues, eventually the populations will get unstable and the food chain will collapse.  (When population density drops below a certain critical level, the growth rate becomes negative and then the decline accelerates exponentially; this is termed the Allee Effect.)

So, we must stop the decline that has been occurring since at least 1899.

Further, we know that increased atmospheric CO2 leads to increased CO2 absorbed by the oceans, which leads to ocean acidification. Worse, the global warming will accelerate that acidification.

In fact, we have seen pH drop from 8.17 in 1940 to 8.03 today. The ocean pH predictions by the IPCC of the three higher-emission scenarios have ocean pH dropping to 7.95 in 2045, 2050, and 2055.

Continued ocean acidification will eventually lead to negative impacts on many of the ocean species, particularly those which construct shells that will have difficulty forming or will even dissolve as the ocean acidification causes undersaturation of calcite and aragonite of which those shells consist. [source of chart: IPCC AR6 WGI SPM Fig SPM.8c]

In the last 70 years, the populations of plankton in our oceans have been cut by half or more. Looking at historical chlorophyll measurements, one estimate is that we have been losing 1% of the median global plankton biomass each year since 1899. [source: DG Boyce, MR Lewis, B Worm, Global phytoplankton decline over the past century, Nature v 466, July 2010]  More recently, analysis of long-term time series data from Narragansett Bay, RI, has revealed that phytoplankton biomass declined 49% from 1963 to 2019. [source: PS Thibodeau, G Puggioni, J Strock, TA Rynearson, Long-Term declines in chlorophyll a and variable phenology revealed by a 60-year estuarine plankton time series, PNAS v121 (21), May 2024]


Phytoplankton is a huge biomass (comparable to all humanity) that serves as the foundation of the ocean food chain. Zooplankton (also comparable in biomass to all of humanity) feed on the phytoplankton, and most shellfish and fish feed directly or indirectly on the plankton. So, as the plankton populations decline, so do the fish populations. [source of figure: M Landos, M Lloyd-Smith, J Immig, Aquatic Pollutants in Oceans and Fisheries, International Pollutants Elimination Network (IPEN), April 2021.]

Global warming will have many additional effects on our oceans. For example, global warming has been slowing many of the ocean currents that distribute the nutrients needed for plankton growth. As global warming continues, it is predicted those currents will decline further.


So, in the 2030 to 2060 time frame, there is a significant chance that the acidification levels and the declining ocean currents are going to accelerate the decline of the plankton populations, and with it the entire ocean food chain populations.


The subsequent mass extinctions will be irreversible. We can't fix them later; removing the CO2 and reversing global warming may be possible; un-extincting our ocean food chain will not be possible.


The widespread famine and other catastrophic effects on our entire planet cannot be overstated.


We need to develop a plan that protects our ocean food chain, even if we fail to achieve Net Zero CO2 Emissions and even if we end up with 2, 3, or even 4°C of global warming. We need to establish "success is assured" for our ocean food chain as soon as possible.

To do that, we need to:

  • Identify all significant causes of the past and existing decline of the plankton populations.

  • Determine the relative sizes of the impacts of each of those causes on the decline.

  • Devise a solution to reverse those declines of the plankton populations, and then show, in advance, that "success is assured".

  • Any knowledge gaps that prevent us from establishing that "success is assured" in advance need to be actively closed as soon as possible.

The purpose of this K-Brief is to expose those knowledge gaps, solicit collaboration from experts on how best to close those knowledge gaps, enabling us to devise a solution where "success is assured". This K-Brief does not yet contain such solution -- but by closing the knowledge gaps to enable proper causal mapping of the declining plankton populations, potential solutions and their effects on the plankton populations will be able to be modeled and shown to be feasible and reliable in the face of the remaining uncertainty, and then optimized for cost and time efficiency.

Achieving Net Zero CO2 Emissions Alone will NOT Save the Ocean Food Chain!

Some readers may be wondering, "Is it not sufficient to achieve Net Zero CO2 Emissions to save the ocean, as we need to do that anyway to stop Global Warming?"  After all, the IPCC has shown that there is strong correlative data that human CO2 emissions have been driving increases in atmospheric CO2 which has been driving global warming, and that both together have been driving ocean acidification, and we know that will eventually lead to decline in plankton populations and eventually collapse of the ocean food chain. That causal chain, as depicted here, undoubtedly exists:

That has lead many proponents of healthy oceans to call for achieving Net Zero CO2 Emissions to save the oceans (especially since we need to stop global warming anyway).


However, focusing on that "solution" to the decline of the ocean food chain will be a grave mistake if that is not in fact the dominant cause of the current decline of the ocean food chain!


If it turns out that achieving Net Zero CO2 Emissions by 2050 (the current objective) does not stop the decline of the ocean food chain, then we could still face those mass extinctions that will be irreversible.


Discovering that is the case after achieving Net Zero in 2050 and realizing that we've lost 25+ years in the battle to save our oceans could be catastrophic!

Correlation does not imply Causation!

Co-Dependence of Zooplankton and Phytoplankton

Furthermore, it is entirely possible that we have some of the causation backwards: that the past decline of the plankton populations is actually the dominant cause of global warming, given the plankton populations could be sequestering more carbon than humans emit, and further has a significant effect on evaporation (the #1 greenhouse gas is water vapor) and cloud formation (which can reflect more heat than it holds in).  Such reverse causation would remain consistent with the correlation data: correlations not only do not imply causation, but also do not imply the direction of the causation.

For those interested in stopping global warming, we dig into that reverse causation alternative in a different K-Brief; so, we will ignore that reverse causation alternative in this K-Brief, instead focusing specifically on the other potential causes of the decline of plankton populations in our oceans (the cloud shapes in the upper left of this reverse causation alternative Causal Map developed in that other K-Brief).

Even the Correlations are not so strong!

Although the correlations between human CO2 emissions, atmospheric CO2, and global warming are very strong (as depicted in the IPCC figure below), the correlation to plankton decline is not so strong.

In the figure below, note the ramp up in emissions in the 1960's lead to ramp up in atmospheric CO2 in the 1970's, and similar ramp up in global warming in the 1970's. In contrast, from 1900 to 1930, global warming was relatively flat; but the plankton populations were already declining at a rate of 1% per year at least as far back as 1899. From a correlation point of view, it seems the plankton populations were being reduced by some other cause than global warming; and given the decline of the plankton populations preceded the global warming, it is more likely the plankton declines caused global warming than were caused by global warming.  [source of figure: IPCC AR6 SYR Fig 2.1abc]

Desirable vs. Undesirable Phytoplankton

Furthermore, the major effects on plankton populations due to ocean acidification will occur when the oceans cease to be super-saturated in calcite and aragonite. To date, our oceans have remained super-saturated in calcite and aragonite, meaning that ocean species with shells made of such won't dissolve. It is predicted that higher latitude areas of our oceans will become undersaturated as soon as 2030, and much of our oceans may be undersaturated as soon as 2060. In limited testing in sea water with the predicted levels of undersaturation, a species of zooplankton showed significant dissolution of its shell in just 48 hours.  Other testing has shown that various species have more difficulty forming shells at the predicted levels of undersaturation. [source: VJ Fabry, BA Seibel, R Feely, JC Orr, Impacts of ocean acidification on marine fauna and ecosystem processes, ICES J Mar Sci 65, 414–432 (2008)]  More research needs to be done to determine how consistently that is true of calcifying ocean species.


So, while that may be devastating to the plankton populations in the near future, that does not at all explain the massive declines that have occurred since 1899 to date.  [source of charts: BI McNeil, RJ Matear, Southern ocean acidification: A tipping point at 450-ppm atmospheric CO2, PNAS 105 (48) 18860-18864 (Dec 2008)]

In summary, the correlations themselves point to there being other causes (beyond the blue causal path) that have been the primary driver of the plankton declines to-date. So, while achieving Net Zero CO2 Emissions may be critical to avoid undersaturations leading to even more rapid declines of plankton in the near future, it won't likely stop let alone reverse the current plankton declines. So, we have urgent need for clarity on those other causes.

It should not be surprising that our earth's biological systems tend to have complex co-dependencies. Given zooplankton eat the phytoplankton, the natural expectation would be that reduced zooplankton would result in increased phytoplankton. Surprisingly, it has been shown that zooplankton population declines due to human pollution actually results in phytoplankton declines. How so?


Every day, the zooplankton dive down hundreds of meters to avoid predators during the day, and rise back hundreds of meters to consume the phytoplankton at night. That Diel Vertical Migration is the largest migration on earth, moving water comparable to the moon-driven tides, and brings the nutrients back to the surface that the phytoplankton need to grow.


Worse, that reduction in the phytotoplankton (zooplankton's food) results in further declines in the zooplankton, further reducing nutrient availability. That can become a positive feedback loop that can collapse the ocean food chain, particularly in areas with lower nutrients or higher pollution and toxins.


Since the biology of plants (phytoplankton) and animals (zooplankton) are quite different, causal analysis of the population declines will benefit from separating out phytoplankton from zooplankton, but showing the co-dependence. So, we have done that here; with a problem flag indicating the dangerous positive feedback loop.

Microplastics and Toxins

Co-Dependence of Whales and Plankton

At the other end of the spectrum from zooplankton, we have whales. Whales are 737-aircraft-sized krill-eating machines; and prior to industrialized whaling, our oceans were filled with millions of such whales. So, you would think that a 5X reduction in the whale population due to industrialized whaling over the past two centuries would be a boon to the krill populations. In fact, the reverse happened...
It turns out that whales feed on krill (zooplankton) throughout the ocean depths and then excrete fatty liquid fecal matter nearer the ocean surface which effectively returns the iron in the phytoplankton consumed by the krill to the surface layer where it is needed to support the photosynthesis by the phytoplankton. One study has estimated that prior to the industrialization of whaling, the whale populations in the southern ocean alone consumed 430 Mt of krill (which is more than double the current population of krill) and recycled 12 Mt of iron each year (which is 10X the current rate of iron recycling). [source: MS Savoca, MF Czapanskiy, SR Kahane-Rapport, et al, Baleen whale prey consumption based on high-resolution foraging measurements, Nature 599, 85–90, 2021]  Beyond just iron, it has been shown that, in the Gulf of Maine, whales bring nutrients from the depths where they feed to the surface at a level greater than the flow of nutrients from all the rivers combined. [source: J Roman, JJ McCarthy, The whale pump: Marine mammals enhance primary productivity in a coastal basin, PLoS ONE, 2010; 5 (10): e13255]
So, the extreme over-fishing of whales that brought whales to near-extinction has dramatically reduced the availability of iron and other nutrients to support the prior levels of phytoplankton biomass, resulting in a massive decline in the entire ocean food chain. We have captured that by adding the three nodes marked with a lightbulb below (we'll use lightbulbs to mark what we add to the Causal Map in each step).

Over-Fishing of More than just Whales

Over-fishing of our oceans is a much wider-spread problem than just whales, but consider one dramatic example: krill. Since the 1970s, krill populations have been reduced by 80%. Krill is a keystone species in the ocean food chain, being the most abundant animal on the planet (trillions of individuals totaling 379 Mt of biomass). The activity of krill and the animals that directly eat krill (e.g., penguins and whales) sequester tremendous carbon in their fecal matter that sinks to the ocean floor. [source: A Hedinger, License to krill: Overfishing the ocean’s keystone species, Apr 2023]


Beyond krill, there is a tremendous level of over-fishing that we do (given the oceans feed a significant portion of the human population) without full understanding of the impacts that fishing may have on the sustainability of that ocean food chain, which can be a recipe for disaster. We need to capture into our Causal Map all those that threaten to destabilize the ocean food chain, especially as the populations continue to decline. For now, we have added just a second "Over-Fishing" node to the prior Causal Map for krill.


Worse, there are important feedback loops in that food chain beyond the two we have already captured. There are surely others between fish, shellfish, zooplankton, and phytoplankton. We need to capture those as well.

Not all ocean plant and bacteria species participate equally in our existing ocean food chain.  Human changes to our oceans can lead to the rise of competing species that do not tend to serve as good food for our existing food chain, or that are even toxic to it. Those competing species can grow to consume most of the available nutrients, causing further decline in the desirable phytoplankton.


Note that this creates another positive feedback loop where the rise of the undesirable leads to further nutrient availability issues that lead to declines in the desirable phytoplankton, which then makes more nutrients and space available to the undesirable phytoplankton.

Note that one of the causes of undesirable phytoplankton is due to Fertilizer Runoff that is often high in nutrients like Nitrogen and Phosphorus that tend to encourage undesirable phytoplankton growth. This points to a weakness in the prior Causal Map:  "Decline of Nutrient Availability" isn't necessarily the problem, but rather an imbalance of nutrient availability that is not well-suited for the desirable plankton growth and/or is better-suited for undesirable plankton growth. To properly model that, we will eventually need to break out the nutrients and capture what is actually balanced. For now, we'll just rename that cloud shape to "Imbalance of Nutrient Availability".

Another cause of undesirable phytoplankton is due to the damming of rivers which reduces the flow of silt down the river and into the ocean. That silt contains many nutrients critical for growth of the desirable phytoplankton. In particular, silt is rich in silicate which is essential for Diatoms to form their shells. With adequate silicate, Diatoms will tend to dominate the other phytoplankton; without adequate silicate, the Diatoms cannot grow, and the undesirable Harmful Algae Blooms emerge. [source: V Ittekkot, L Rahm, DP Swaney, C Humborg, Perturbed Silicon Cycle Discussed, Eos, v81 n18, 2000 May 2]

Note that such blooms of undesirable plant life are already becoming common. For example, there is a 13 Mt mass of sargassum in the Atlantic ocean that is twice the width of the continental US and is becoming a toxic problem for the beaches as it decomposes, releasing hydrogen sulfide and the associated stench. More importantly, it can choke out other ocean species and smother coral. [source: NASA Earth Observatory, A Massive Seaweed Bloom in the Atlantic, Mar 2023] 

Future-Proofing: Warming is Coming!

Unfortunately, 80% of human wastewater is dumped untreated into oceans (or into rivers destined for oceans). [source: UN, Water Quality and Wastewater]  Worse, even when the wastewater is treated, it does not remove microplastics nor many of the other toxins that will kill ocean life. Even worse, most of that is not destined to sink to the ocean floor, but will tend to float at the surface. In particular, the hydrophobicity of the lipid surface microlayer (SML) will tend to attract and hang onto hydrophobic and lipophilic toxins until consumed by zooplankton trying to feed on the phytoplankton which generates the lipids in the surface microlayer. That surface microlayer tends to have 500X concentrations of pollutants. [source: O Wurl, JP Obbard, A review of pollutants in the sea-surface microlayer (SML): a unique habitat for marine organisms, Marine Pollution Bulletin, v48n11-12, Jun 2004]  And the toxins that don't kill the zooplankton or the fish that eat the zooplankton tend to accumulate in their bodies; the long-term impacts of that accumulation on the ocean food chain and on seafood-eating human health remain unclear. [source: LM Ziccardi, A Edgington, K Hentz, KJ Kulack, SK Driscoll, Microplastics as vectors for bioaccumulation of hydrophobic organic chemicals in the marine environment: a state of the science review,  Environmental Toxicology and Chemistry, v35n7, 1667–1676, 2016]  As an early indication of such accumulation, a recent study found microplastics in every human placenta that was tested. [source: MA Garcia, R Liu, A Nihart, et al, Quantification and identification of microplastics accumulation in human placental specimens using pyrolysis gas chromatography mass spectrometry, Toxicological Sciences v 199 (1), May 2024, pp 81-88]  Similarly, another recent study found microplastics in every human testicle tested, which could be the cause of decades of decline in human sperm counts. [source: CJ Hu, MA Garcia, A Nihart, R Liu, et al, Microplastic presence in dog and human testis and its potential association with sperm count and weights of testis and epididymis, Toxicological Sciences, early access May 2024]

Note that not all toxins come from human sources. In particular, those undesirable phytoplankton populations can produce toxins that will similarly build up in the ocean and its fish populations (and those that eat those fish). The toxins produced by cyanobacteria is of significant concern.

Imbalance of Nutrient Availability will be Key

Alternative Remedies

There remains a gap between government policy and IPCC recommendations on the needed timing to achieve Net Zero CO2 Emissions.  [source of figure: IPCC AR6 SYR Fig 3.6]


Worse, note that the IPCC's paths that keep global warming below 1.5°C require immediate action starting in 2020. That has not happened, despite the currently implemented policies being predicted to result in global warming in excess of 3°C. Thus, there is a much larger implementation gap noted by the IPCC, such that achieving Net Zero CO2 Emissions is currently fairly unlikely.  [source of figure: IPCC AR6 SYR Fig 2.5a]

Further we have argued in a separate K-Brief that there is a significant chance that Net Zero CO2 Emissions alone will fail to stop global warming. And others have warned that there is significant warming "in the pipeline" -- warming that will occur but has so far been delayed by various mechanisms. [source: JE Hansen et al, Global warming in the pipeline, in review 2023]  So, there is high likelihood that more global warming is coming soon. Estimates from 2 to 4°C are common and likely; much higher estimates have been suggested.

So, although that blue causal path above has probably not had much effect so far, it will likely have strong effect in the near future. So, it is critical that our plans to protect the ocean food chain are ready to deal with the consequences of higher CO2 and higher temperatures of both the air and the ocean.


One of the additional effects of global warming is the reduction and likely elimination of the major ocean currents, including the AMOC, the NADW, and the AABW.  Reduction of the latter has been shown to greatly reduce oxygen availability [source: KL Gunn et al, Recent reduced abyssal overturning and ventilation in the Australian Antarctic Basin, Nature Climate Change (2023)], and other nutrient availability is likely impacted as well.

Another effect of higher temperatures is that the more temperature sensitive species are migrating to higher latitudes (cooler waters). To the extent that migration is uneven or pushes them into waters without stable supply of the right nutrients, it could further hasten the collapse of the ocean food chain.

One element of this evolving Causal Map is of particular concern as it is connected to everything, and thus key to establishing that "success is assured": the variety of impacts on nutrient availability. The next steps in the evolution of this Causal Map will include:

  • Breaking out the specific nutrients needed by phytoplankton.

  • Relations showing the relative amounts of nutrients needed by desirable phytoplankton and that the phytoplankton growth will be a function of whichever nutrient is least available vs. the need.

  • Breaking out the levels of nutrients that tend to grow undesirable phytoplankton, and conversely which nutrients get consumed by that undesirable phytoplankton.

  • Relations showing the quantitative impact on each of the different nutrients' availabilities.

  • The specific quantitative impacts of toxins and other pollution on the growth of desirable species vs. undesirable species.

  • Quantitative modeling of potential solutions to the problems that could be implemented.


Beyond those next steps in the Causal Mapping above, we have urgent need to establish some scientific consensus on:

  • what has been driving the massive decline in the plankton populations for the last century (what should we learn from the past; and what do we need to urgently correct)

  • the timeline for the collapse of our ocean food chain (how much time do we have, and what are the earliest drivers that need to be delayed first)

  • which of the positive feedback loops could result in runaway behavior that could suddenly accelerate that collapse

  • what can we do to slow or reverse the various paths towards ocean food chain collapse

The best way to establish such scientific consensus is to construct visual models of the causally-sound scientific evidence to facilitate efficient discussion among those with different expertise, such that those experts can see where their knowledge properly connects with the rest.  (The role of this K-Brief is to collect those visual models into a cohesive story for engaging experts in such discussion.)

All of the above knowledge gaps need to be closed as soon as possible such that a concrete plan can be laid out where "success is assured" for halting (or preferably reversing) the plankton population declines.

To do that, we need to move beyond correlative studies to causal experimentation to determine the true cause & effect relationships. Correlative studies can only point to possible causal effects (or reject causal effects); to understand the causation, you need controlled isolated experimentation that can minimize confounding variables, and determine reasonably precise mathematical cause-and-effect relationships.

This K-Brief is not a static document. It is intended to make visible what we believe we know such that people with expertise in these scientific areas can identify where they can contribute their knowledge and how it should be incorporated into the K-Brief and the rest of the knowledge it is making visible.

Further, note that we are not just looking for existing knowledge; we are also looking for expertise on how to most efficiently experiment to close knowledge gaps by developing new knowledge. Knowledge of experimental techniques, measurement techniques, sources of data, isolation techniques, and so on are sought.

So, if you have expertise in any area of this K-Brief, and are willing to point out anything that should be corrected or improved in it, please contact us at SaveOurOceans@TargetedConvergence.Com -- we will continue to evolve this K-Brief accordingly. Our goal is to help facilitate the identification and closing of the knowledge gaps, and thereby accelerate us in the search for more optimal solutions for which we can establish that "success is assured" that our ocean food chain will remain safe, and thus humanity safe from the consequences of the ocean food chain collapsing.

By closing the knowledge gaps in the Causal Analysis above, potential remedies to the problem will tend to become apparent. And the Causal Maps will then allow you to explore the different cost-benefit trade-offs in selecting the more desirable of those alternative remedies.

At this time, we have not yet closed those knowledge gaps; and thus, the root causes remain unclear. So, this block remains a placeholder for that future analysis.

However, given the urgency, we do propose a potential partial remedy in this separate Remedy K-Brief. We chose to separate that Remedy out because: (a) it can potentially remedy more than just this Problem; and (b) we don’t want to short-circuit the ongoing analysis of the root causes of this problem, which should remain the focus of this Problem K-Brief.

We all know that correlation does not imply causation.  And there are numerous examples where assuming it does has resulted in very bad decisions. So, whenever causation is being concluded based on correlation, it is critically important to consider alternate causal models that could be consistent with that correlated data, and then find ways to test or otherwise determine which of the causal models is correct, before settling on a set of decisions based on any one of the causal models, OR to find a set of decisions that work fine regardless of which causal model is correct (such that we know "success is assured" in any case).

In the same time period as our correlative data, we know that human activities have increased numerous things that have negative impacts on the assumed causal chain presented above. If any one of the additional causal paths marked with ?-marks below are comparable in size to the blue path, then a solution that only mitigates the blue path may not solve the problem!

The remainder of this K-Brief will not try to enumerate all other possible causal models.  That effort should be undertaken, but is beyond the scope of this K-Brief.  Rather, the remainder of this K-Brief will focus on just the direct path marked with a flag below.

Call for Expertise and Consensus Building

We would like to acknowledge help provided by the following people in pointing us to many of the sources of the knowledge captured here:


And of course, we acknowledge all the many experts in the various scientific and engineering topics whose knowledge is captured here, particularly those listed with the [source: __] designations throughout.  But many of those sources were, in turn, built on the expertise of those that they cite.

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