Mapping the global distribution of phytoplankton

ETH Zurich


IMAGE: Phytoplankton boasts an amazing variety of forms and species. Credit: Meike Vogt und Jorge Martinez-Rey / ETH Zurich

With some 10,000 to 20,000 different species in the world’s oceans, the diversity of phytoplankton (phyto from the Greek for plant) species is extremely rich. These phytoplankton form a key element of ocean ecosystems and life on this planet, producing more oxygen than all the world’s rainforests combined. They also serve as the fundamental basis of the marine food chain.

To date, however, very little has been known about the geographic and seasonal diversity of phytoplankton. Although many species of phytoplankton have been identified, the question of when and where they occur is largely unexplored; in light of the current biodiversity crisis, this represents a serious knowledge gap.

In early May, the Intergovernmental Platform on Biodiversity and Ecosystem Services stated in its latest report that a million of all known species on earth are under threat of extinction as a result of human activity and climate change. However, for many important species, especially species of the world’s smallest form of marine life, plankton, our knowledge of their distribution and diversity remains inadequate or non-existent to this day.

Now, a team of researchers from ETH Zurich and the Swiss Federal Institute for Forest, Snow and Landscape Research WSL have filled in some of this knowledge gap. In a study published recently in the Science Advances journal, they modelled the spatial and temporal distribution of over 530 different species of phytoplankton. As the basis for their distribution charts, they used around 700,000 water samples from across the world’s oceans.

Biodiversity in tropical seas

Their study reveals that tropical waters hold the richest diversity of species at all times of the year. Phytoplankton diversity is particularly high in the seas of the Indonesian-Australian archipelago, in parts of the Indian Ocean and in the equatorial Pacific Ocean. In the subtropics, biodiversity drops off markedly beyond 30 degrees latitude North and South, reaching its lowest values around a latitude of 55 degrees. Diversity then picks up again slightly towards the poles.

“We were surprised to find that on a monthly basis, the polar seas present greater diversity than the mid-latitudes,” says Damiano Righetti, the lead author of the study. He is a PhD student with ETH professor Nicolas Gruber and senior scientist Meike Vogt. “It’s remarkable because global species distribution and diversity are normally closely linked to environmental temperature trends.”

Species diversity typically decreases continuously towards the poles, where it is normally at its lowest. Temperature could plausibly be the direct driver of this decline. According to metabolic theory, higher temperatures accelerate metabolism, mutations of genetic material and speciation. This explains why the tropics are richer in species than the mid-latitudes and the polar regions, as would be expected.

Biodiversity surprisingly low at mid-latitudes

The study reveals that phytoplankton does not always behave in line with this theory. “Evidently, there are factors other than temperature affecting plankton diversity,” Righetti says. Two of these might be the strong currents and turbulence, which are prevalent in the mid-latitudes, but less so in polar or tropical seas. “The seasonal fluctuations and ocean turbulence in these latitudes might suppress the development of biodiversity, even though the temperatures here are higher than in the polar oceans,” the ecologist says.

Righetti and colleagues also found that phytoplankton diversity in the mid-latitudes, unlike in the tropics, varies greatly from season to season. Righetti explains that although the number of species in the mid-latitudes is constant over time, the species composition changes over the course of the year: “In contrast to tropical seas, the diversity here is dynamic throughout the year, but hardly any research has been done on this.”

Samples collected on shipping routes

Working with ETH adjunct professor Niklaus Zimmermann and other colleagues from the WSL, Righetti developed a computer model to map the diversity distribution of phytoplankton. They fed this model with observational data and used it to project where each species occurs – with a temporal resolution of one month.

The observational data came from water samples collected during research trips as well as from normal shipping routes. Phytoplankton specialists subsequently studied the samples under the microscope to determine which species they contained. Over time, these research cruises amassed huge amounts of observational data on several thousand different species. Righetti and colleagues then gathered the data available into a database and analyzed it.

It must be noted, however, that sampling has not been evenly distributed across the oceans and, in many regions, has not spanned all seasons. Thanks to British researchers, the North Atlantic is very well represented, but very little data exist for large parts of the other oceans. The ETH researchers compensated for this distortion in their models.

Their work is significant in a number of respects. Not only are their distribution maps the first to chart phytoplankton; their models can also be used to predict how the diversity of phytoplankton could develop under changing temperature conditions. Warmer waters as a result of climate change could alter the distribution of phytoplankton. “In turn, this could have a serious impact on the entire marine food chain,” Righetti says.


From EurekAlert!

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May 22, 2019 10:08 pm

I’m sorry, but when a paper says:

“In early May, the Intergovernmental Platform on Biodiversity and Ecosystem Services stated in its latest report that a million of all known species on earth are under threat of extinction as a result of human activity and climate change. ”

… it goes directly into the circular file. Anyone who believes that kind of madness is of no interest to me.


Reply to  Willis Eschenbach
May 23, 2019 3:15 am

Would a species be a species if it wasn’t always under the threat of extinction? 😎

Joshua Peterson
Reply to  Willis Eschenbach
May 23, 2019 5:11 am

It’s worth noting that the paper followed that line with the scientific equivalent of, “But that’s cow dung, and here’s why.”

Reply to  Willis Eschenbach
May 23, 2019 6:00 am

Well, considering that most experts in the fields of biology believe that the total number of species on the planet exceeds one trillion, it would be a shock if there weren’t at least one million – 0.1% – of those species being on the road to extinction at any given time in earth’s history.

It’s called natural selection.

Reply to  Duane
May 23, 2019 6:05 am

Oops, my bad .. or at least my math was bad.

One million species being in trouble out of one trillion total species is 0.0001%, not 0.1%, of the total.

Again, the point is, due to natural selection and well known constant changes in climate over the geological timescales of earth’s history, it would be a shock if there weren’t at least 0.0001% of species at risk of extinction.

Reply to  Duane
May 23, 2019 6:07 am

“Well, considering that most experts in the fields of biology believe that the total number of species on the planet exceeds one trillion”

That sounds exceedingly unlikely. Reference please.

Reply to  tty
May 23, 2019 6:34 am

How many species?

To now, the best approximation of Earth’s species total was based on the educated guesses and opinions of experts, who variously pegged the figure in a range from 3 to 100 million — wildly differing numbers questioned because there is no way to validate them.


When applied to all five known eukaryote* kingdoms of life on Earth, the approach predicted:

  1. ~7.77 million species of animals (of which 953,434 have been described and cataloged)
  2. ~298,000 species of plants (of which 215,644 have been described and cataloged)
  3. ~611,000 species of fungi (moulds, mushrooms) (of which 43,271 have been described and cataloged)
  4. ~36,400 species of protozoa (single-cell organisms with animal-like behavior, eg. movement, of which 8,118 have been described and cataloged)
  5. ~27,500 species of chromista (including, eg. brown algae, diatoms, water moulds, of which 13,033 have been described and cataloged)

Total: 8.74 million eukaryote species on Earth.

As many as there needs to be to perpetuate the biodiversity crisis fraud.

Reply to  Duane
May 23, 2019 9:15 am

The statistical method used in that study is invalid:

Reply to  Duane
May 23, 2019 10:41 am

Didn’t read your own link?

“There Might Be 1 Trillion Species on Earth”

The operative word is might. That is; Fantasy masquerading as science.

It is so typical of duane and alarmists who peddle eco and climate nonsense.
Find a threat then enlarge and emphasize that threat into theoretical Earth disaster. Then attempt to stuff that nonsense into all owned news channels and fake science publications.

It is known as making mountains out of molehill dung.

Reply to  Willis Eschenbach
May 23, 2019 6:36 am

Note the weasel words “human activity and climate change”. You could have said “human activity and Santa Claus” and it would have been equally true (or untrue).

Human activity (overhunting, overfishing, deforestation, destruction of habitat in general, introduction of invasive species…) threaten a lot of species, climate change does not.

bruce ryan
Reply to  Willis Eschenbach
May 23, 2019 7:37 am

Willis, wasn’t your observation of the equatorial seas as being clear blue? As you approach islands the seas green up.
I’d like to see where their shipping samples were taken. The fact that they modeled so much of their findings I do have some reservations.

Reply to  bruce ryan
May 23, 2019 9:16 am

Blue is the desert color of the ocean.

John in Oz
Reply to  Willis Eschenbach
May 23, 2019 5:04 pm

If the vegans and ‘cows are an existential threat to mankind because they produce methane’ crowd get their way, will bovines be placed on the threatened with extinction due to mankind list?

J Mac
May 22, 2019 11:23 pm

Gotta agree with Willis. I hit that line of drivel… and ceased hope for anything substantive to follow.

May 22, 2019 11:30 pm

The main issue is that they only talk about diversity and ignore density. So sample a given volume of water and find a thousand phytoplankton all different species and that is high diversity; sample the same volume of water and find a million phytoplankton all the same species and that is low diversity. I am wondering if a low density of phytoplankton is the reason diversity rises above 55 deg.

Within that limit this seems to be a reasonable study, up to the point that they put the obligatory climate change bad paragraph. The study seems to show that warm waters are beneficial, but they still say “Warmer waters as a result of climate change could alter the distribution of phytoplankton. ‘In turn, this could have a serious impact on the entire marine food chain,’” I suppose if you distort the English language enough, an increase in phytoplankton and hence larger sea creatures could be described as “a serious impact on the entire marine food chain” a seriously beneficial one.

Reply to  BillP
May 23, 2019 12:41 am

Yep. There was the guy who dumped tons of iron in the Pacific and the plankton bloomed and the salmon came back. The powers-that-be didn’t like that at all. link

As far as I can tell, the increase in atmospheric CO2 is just as easily explained by a decrease in plankton as it is by burning fossil fuels.

May 23, 2019 12:17 am

Lets assume that he Green blob is right, and that the world is getting hotter. So what happens in the Oceans, do these tiny creatures get bigger, smaller, greater or less in total volume. , or is there more or less variety. ? Not all that clear.


Reply to  Michael
May 23, 2019 1:23 am

They turn into godzilla and come and eat you and your family, standard Climate Change science.

David Channon
May 23, 2019 12:29 am

Sir Alistair Hardy Foundation for Ocean Science has been collecting plankton data since 1931. More here

May 23, 2019 2:28 am
Reply to  griff
May 23, 2019 5:17 am

I always wondered how micro-paleontology started… 😉

May 23, 2019 2:39 am

Off-piste everyone and sorry for that but good to get some humour in-

“Comedy Unleashed on Greta Thunberg”

May 23, 2019 2:56 am

There are two areas whch need to be assessed to better understand climate; phytoplankton consumption of carbon dioxide and under water volcanic explosions. If we do not know the mass of phytoplankton and the rate at which it consumes carbon dioxide, how can we model climate ? How much carbon dioxide and minerals do underwater volcanic erruptions produce ? The input of minerals and carbon dioxide could find their way to the surace and fertilise phytoplankton ?

Thomas Homer
May 23, 2019 5:34 am

” [Phytoplankton] also serve as the fundamental basis of the marine food chain.”

Since Phytoplankton consume Carbon Dioxide, the above claim should read:

CO2 is the fundamental basis of the marine food chain.

CO2 feeds life, on land and sea.

Ian Wright
May 23, 2019 5:35 am

I am a tad confused. If we don’t know how much phytoplanktons are, but we know they take CO2 out of the system in their skeleton formation process (which then blankets the sea as a CaCo3 ooze) how the heck are we so sure about this anthropgenic CO2 lark?

May 23, 2019 6:19 am

It is important to distinguish diversity and density. Tropical areas typically have high diversity but low density of iundividuals, colder area lower diversity but higher density while both are low in the Arctic/Antarctic (on land that is).

This is a bit different in oceans. Warm waters are nutrient-poor, and this is particularly true for the “doldrums” in mid latitudes which are oceanic deserts. But in the oceans the density of phytoplankton is actually highest in the Arctic/Antarctic where nutrients are continually being dumped into the oceans by melting glacier ice. Here is a satellite map for chlorophyll (=phytoplankton) density:

May 23, 2019 6:29 am

“With some 10,000 to 20,000 different species in the world’s oceans, the diversity of phytoplankton (phyto from the Greek for plant) species is extremely rich.”

I would say the opposite. That is a surprisingly low number of species, considering their small size and that 70 % of the World is Ocean. It means that there is only barely more species of phytoplankton than there are species of birds (something like 11,000 species at present).

Robert W Turner
Reply to  tty
May 23, 2019 8:22 am

Perhaps because the marine environment is relatively homogeneous whereas terrestrial environments are geographically segregated, leading to more allopatric speciation. They are also much more easily observed and the difference between species, subspecies, and variant is often murky.

Also, 10,000 is too low of an estimate, given that there are over 10,000 species of forams alone.

Robert W Turner
Reply to  Robert W Turner
May 23, 2019 9:10 am

Well I suppose since most forams are benthic and not actually planktonic then 10,000 might not be too low.

Reply to  Robert W Turner
May 23, 2019 9:24 am

Forams aren’t phytoplankton, they are protists, and most species aren’t even planktonic.

Robert W Turner
Reply to  tty
May 23, 2019 10:29 am

Hah, I didn’t even notice they were only studying phytoplankton, I thought it was all plankton. Protists can be considered phytoplankton – it’s a common term simply referring to any photosynthesizing plankton, not a scientific term restricted to the plant kingdom. A few foram species could arguably be considered phytoplankton.

May 23, 2019 7:16 am

“According to metabolic theory, higher temperatures accelerate metabolism, mutations of genetic material and speciation. This explains why the tropics are richer in species than the mid-latitudes and the polar regions, as would be expected.”

This line caught my eye. The metabolic theory is a reasonable hypothesis. The conclusion presented is an inexplicable jump. The tropics are much more likely to be diverse because conditions are much more conducive to living. Heat makes growth of anything easier. Every environment in the tropics has more species than the Antarctic ice(surprisingly abundant). Cold is huge stressor on any living thing. Heat can be coped with because there is energy available to deal with it.

Johann Wundersamer
Reply to  Philo
May 27, 2019 5:52 am

According to metabolic theory, higher temperatures accelerate:

mammalian metabolism,

Robert W Turner
May 23, 2019 8:09 am

This paper sounds like amateur hour.

First they mention Chicken Little’s 6th mass extinction claim, then they sound like research on plankton distribution and populations have never been done. They don’t mention anything about sampling location specifics – open ocean, shelf, embayment, brackish, hypersaline – as if a sample from x latitude is just the same as any other sample from x latitude. Nothing mentioned about how diversity compares to overall productivity.

And then they exclaim surprise that the high latitudes show an increase in diversity. Have they not heard of diatoms or dissolved nutrient limiting factor on primary production?

Kurt Linton
May 23, 2019 9:05 am

“our knowledge… remains inadequate or non-existent to this day.” Of course, that is completely irrelevant.

HD Hoese
May 23, 2019 9:54 am

Global pattern of phytoplankton diversity driven by temperature and environmental variability
Open Access
Supplementary Materials for Global pattern of phytoplankton diversity driven by temperature and environmental variability

“Fig. S5. Species richness–temperature relationships derived from the observational raw data. Fig. S6. Species ranges for key environmental factors. ……Expert validation led to the exclusion of 503 species names that could not be traced to any taxonomic entity on Algaebase, which was either accepted or preliminarily accepted, leaving 1938 species names”

Unfortunately the word “richness ” refers to the number of species but there have been several complications that try to measure diversity “better.” There are lots of links on the subject. I have not read about “The metabolic theory of ecology,” but would presume that it includes nutrients, especially those often limiting in the ocean. When I took oceanography, before the Anthropocene, we were taught that the ocean was largely a desert. Various schemes over the years have been proposed to change it, but a great deal of the nutrient literature is devoted to presumed excesses. The word eutrophic is misused as such septic systems that cause problems are “hypertrophic.” The ocean is still largely oligotrophic but I have not been out there lately and base this on second-hand information that is consistent with sailing miles and miles without seeing much more than water.

From Figure S6
“Variables in A to I are the most powerful correlates of global SDM-based species richness besides temperature and latitude: MLPAR, mixed-layer photosynthetically available radiation; PAR, photosynthetically available radiation; Chl, chlorophyll a concentration; pCO2, sea surface partial pressure of CO2.

This is a difficult paper to review with an impressive list of species. It appears from a too cursory examination that it shows that nutrients are far more important than CO2.
“The five highest values (top five performing variables) per column are highlighted in bold font.”
T, Wind, PAR, NO3, MCPAR, best as I can tell from what is bold in the table S2.

That they found the most species in the tropics is not surprising. Shall we conclude that increasing temperature is good for “species richness?” Lots of assumptions, interesting paper, but needs a better title.

“….responses of global patterns in marine phytoplankton diversity to climate change may be more complex than hitherto anticipated, …” from end of results and discussion is not quite the same as the last line of their abstract–“The nonmonotonic relationship between phytoplankton richness and temperature suggests unanticipated complexity in responses of marine biodiversity to ocean warming.” Where have I heard that before?

May 23, 2019 10:24 am
David Schnare
May 23, 2019 10:27 am

The paper does not seem to have addressed the change in nutrient loading, which also vary over a year. Without that, they have a massive hole in their methodology and ultimately any conclusions they offer

May 23, 2019 1:34 pm

While I don’t have access any longer to the references I might note, as some have mentioned, that it was once believed tropical oceans were near “deserts” relative to the number of phytoplankton both in species diversity and density. I debated with one of the world’s experts in dinoflagellates for nearly a decade. Why? Swordfish, marlins, dolphin (fish), yellow fin tuna, bluefin tuna all travel to the tropics to spawning. Yellow fin and dolphin are extremely fast growing and seldom leave sub-tropical and tropical oceans. SO why would they travel so far if the tropical oceans were deserts. Well they aren’t the deserts some in the past have preached. Turns out that scientists studying tropical phytoplankton were not using the correct sampling methods. Basically their “nets” had too large a mesh size. Micro-phytoplankton, most species never before identified, were slipping through and going unidentified and uncounted. They went to a smaller mesh—-

Ever want to be amazed find a research vessel with the right depth recorder/ sonar and watch what happens with plankton at night in the tropics.

The bottom line is we know damn little about the ocean, far less than we know about the surface of the Moon.

May 23, 2019 4:08 pm

It’s called the Deep Scattering Layer and it moves Up and Down in response to the Sun. At night it comes Up and at dawn it goes Down. Oceanographers have studied it for decades.

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