What are Phytoplankton?

Phytoplankton are microscopic marine plants that live suspended in water, both salty and fresh, and drift with the currents. Despite their small size, there are more phytoplankton suspended just below the water’s surface than stars in the sky.

Why are Phytoplankton Important?

NASA satellite studies show that the greenness of the ocean varies widely year to year, decade to decade. It would take many decades of data to see if there's a long-term trend

THEY generate about half OF the atmosphere's oxygen 

Despite their tiny size, phytoplankton are critical to much of life on Earth. Much of the oxygen in our atmosphere today was produced by phytoplankton or phytoplankton precursors over the past 2 billion years.

Phytoplankton also form the base of the marine food web

They are eaten by primary consumers such as zooplankton, which in turn provide food for small fish, and so on all the way up the food chain to top predators like dolphins, large sharks, whales, and seals. Humans consume aquatic life from every section of this food web. 


THEY regulate the global climate  

Phytoplankton play an integral role in moderating the Earth's climate. Carbon dioxide emissions—like the kind that cars produce—are absorbed by phytoplankton on the ocean surface. In Fact, Scientists believe that the oceans currently absorb 30-50% of the CO2 produced by the burning of fossil fuel. When they die, they sink, and carry this atmospheric carbon to the deep sea. A fraction of this organic matter will be trapped in sediment layers and after millions of years will become fossil fuels. This is a process called the “biological pump.” By reducing the levels of atmospheric CO2, phytoplankton are a significant force in limiting global warming and maintaining the climatic health of the planet.

So what?


Any change in phytoplankton productivity could have a significant influence on biodiversity, fisheries and the human food supply, and the pace of global warming. Today, Phytoplankton are being harmed by pollutants in the ocean, such as agricultural and industrial runoff, and are often absent where pollutant concentrations are high. Phytoplankton also need nutrients to grow, particularly nitrogen and phosphorus, which can be scarce in warm surface waters.

Key Research

Global Phytoplankton Decline Over the Past Century

Without phytoplankton, most, perhaps all, of the animals in the food web would die off, and ultimately, our supply of breathable air would be cut in half. A 2010 study in the journal Nature found that populations of phytoplankton have decreased by 40% since 1950. Since 1899, the average global mass of phytoplankton has shrunk by 1%each year.

Mathematical Modeling of Phytoplankton—Oxygen Dynamics Under Climate Change

Global warming could affect phytoplankton and the amount of oxygen available in our atmosphere.  If the world’s oceans warmed just 6 degrees, phytoplankton would halt oxygen production. By 2100, the oxygen levels at sea level could be the same as those at the top of Mount Everest.

A Reduction in Marine Primary Productivity Driven by Rapid Warming Over the Tropical Indian Ocean

In the past 6 decades, the Indian ocean has seen a reduction of up to 20% of marine phytoplankton. The observations indicate that phytoplankton have decreased up to 30% during the past 16 years. The reduction in marine productivity is attributed to the rapid warming of the Indian Ocean. Changes in plankton production can have immense impact on marine species as well as humans.

Reconciling fisheries catch and ocean productivity

There are large regional differences in fish catch depending on the condition of the ocean plankton pastures those regions sustain. The models show that even modest to moderate declines in phytoplankton production, of up to 15%, could result in fish catch decreases that may exceed 50%.

 Southern Ocean Phytoplankton in a Changing Climate

Phytoplankton in the Southern Ocean, which plays a key role in reducing atmospheric carbon, face extinction. The level of global atmospheric carbon would be around 50 percent higher without the uptake provided by Southern Ocean phytoplankton.

Decline in global oceanic oxygen content during the past five decades

Reports on stunning 2% decline in ocean oxygen in just 50 years, it will plummet to a 7% loss before the end of this century!

Biomass changes and trophic amplification of plankton in a warmer ocean

Estimated than an increase in ocean temperature due to global warming would cause phytoplankton and zooplankton biomass to decrease by 6 percent and 11 percent, respectively, by the end of this century.


Additional Reading: 

What’s happening to the oceans’ phytoplankton?

Failing phytoplankton, failing oxygen: Global warming disaster could suffocate life on planet Earth

Warming Ocean Slows Phytoplankton Growth

Global Warming is Putting the Ocean's Phytoplankton in Danger

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