Mighty Phytoplankton Fills the Earth with Oxygen
- Alina Bradford
- Apr 16
- 5 min read
Updated: May 7
Besides Feeding Marine Life, Tiny Algae Also Trap Carbon Gases
Aside from a miraculous case of how an Italian teenager survived for 42 minutes underwater without oxygen in 2015 or Stéphane Mifsud’s static apnea (holding one’s breath without moving) underwater world record of 11 minutes and 35 seconds in 2009, air—rather, oxygen—is something human beings can’t literally live without.
When thinking of oxygen production, lush forests and leafy green plants often come to mind. But surprisingly, most of the oxygen people breathe doesn't come from trees—it comes from the ocean. It’s estimated that phytoplankton produce over 50% of the Earth’s oxygen, making them the unsung heroes of the atmosphere.
It’s estimated that phytoplankton produce over 50% of the Earth’s oxygen, making them the unsung heroes of the atmosphere.
Phytoplankton (or microalgae) are tiny, plant-like organisms floating near the ocean’s surface (in the euphotic zone, usually the top 200 to 300 meters or about 656 to 984 feet). These microscopic powerhouses perform photosynthesis, using sunlight, water, and carbon dioxide to produce energy and oxygen.
Though invisible to the naked eye (ranging from less than 1 micrometer to over 100 micrometers), phytoplankton exist in vast numbers and support the foundation of marine ecosystems. Without phytoplankton, not only would marine life collapse, but humans and all land animals would struggle to survive due to the drastic drop in atmospheric oxygen. Their ecological importance is matched only by their potential in fighting climate change, thanks to their ability to store carbon in the deep ocean.
Phytoplankton’s Role in Marine Ecosystems
Phytoplankton are the base of the aquatic food web. In addition to feeding zooplankton—tiny animals in the ocean—phytoplankton are eaten by larger creatures like fish, whales, and seabirds. In this way, plankton support life from the smallest shrimp to the largest blue whales.
“But the important takeaway is that we are all members of this food web,” Reagan Errera, PhD, a research ecologist at the National Oceanic and Atmospheric Administration, said in a 2019 Tedx Talk. “Starting with the phytoplankton, moving up through fish and shellfish, and ending potentially with humans, ‘the small’ have a big impact on our drinking water, seafood industry, and ecosystem and human health.”
“Starting with the phytoplankton, moving up through fish and shellfish, and ending potentially with humans, ‘the small’ have a big impact on our drinking water, seafood industry, and ecosystem and human health.”
Without phytoplankton, marine biodiversity would crash. Fish populations would dwindle, affecting both natural ecosystems and global fisheries that feed millions. Coral reefs, which depend on healthy zooplankton populations, would also struggle, affecting coastal communities and ocean tourism.
Tracking Phytoplankton Populations
To understand how many phytoplankton are in the ocean, scientists monitor levels of chlorophyll, the green pigment in plants that captures sunlight for photosynthesis. Chlorophyll is like a glowing marker that satellites in space can detect, with high levels indicated in dark green.
According to NASA, satellite images can track the global distribution of phytoplankton. These colorful maps help scientists understand how ocean health changes with the seasons, pollution, and climate patterns like El Niño. The data also help predict events like algal blooms—when phytoplankton grow out of control.
Phytoplankton and ‘Dead Zones’
While most phytoplankton are beneficial, under certain conditions, they can become dangerous. When oceans or lakes get too many nutrients, especially from agricultural runoff or sewage, phytoplankton can grow too fast. These events are called harmful algal blooms (HABs). Some species produce toxins that can kill fish, poison shellfish, and even harm people who swim in contaminated water.
“Dead zones” are areas in the ocean with little to no oxygen; they can form when large phytoplankton blooms die and sink. As bacteria break the blooms down, they use up the surrounding oxygen. Marine animals flee or die, and ecosystems can take years to recover.
Powerful Carbon Sequestration
On the positive side, phytoplankton offer a natural solution to climate change.
During their daily photosynthesis, they absorb over 100 million tons of carbon dioxide (CO2)—the gas most responsible for climate change. Some of the carbon gets stored in the phytoplankton’s bodies. When they die, some sink to the bottom of the ocean, taking the carbon with them. This process, known as the biological carbon pump, helps reduce the amount of CO2 in the atmosphere.
“Once [coccolithophores (a type of phytoplankton)] bloom, once they die, not only do they take the sugar carbon they produce, they also take the calcium carbonate—the inorganic chalky material—to the bottom of the ocean,” said Ivona Cetinić, PhD, senior research scientist at NASA Goddard Space Flight Center’s Ocean Ecology Laboratory in a 2023 video. “So, they’re really good for exporting carbon—removing it from this contact with the atmosphere.”
“So, [coccolithophores are] really good for exporting carbon—removing it from this contact with the atmosphere.”
However, the 7th Copernicus Ocean State Report in 2023 by the Copernicus Marine Service, a program of the European Union, indicated that climate change itself is a concern for phytoplankton: “Climate-induced changes causing temperature rise, ocean acidification and ocean deoxygenation stress the ocean’s contemporary biogeochemical cycles and ecosystems, thereby impacting the phytoplankton communities,” it said.
Despite this concern, the report indicated that “most phytoplankton functional types remained stable over the period 2002–2021, except for prokaryotes [plankton without a nucleus], which slightly declined over this period,” based on a study in the report.
Some scientists are exploring artificial ocean fertilization, where nutrients are added to stimulate phytoplankton growth to store more carbon. However, this approach remains controversial due to unknown side effects.
Cultivating Phytoplankton at Home
Cultivating phytoplankton can be a great way to feed one’s aquarium tank and support healthy ecosystems. Many reef tank owners also use home-grown phytoplankton to feed corals, clams, and filter feeders.
Here’s a basic guide to growing phytoplankton at home:
Start with a culture. Purchase a starter culture of live phytoplankton from a trusted supplier.
Get the right equipment. Clear containers (like 2-liter bottles), an air pump, airline tubing, and a light source. Maintaining clean equipment and consistent conditions is key to preventing contamination.
Add nutrients. Use a special phytoplankton fertilizer mix, often sold as "Guillards F/2" or similar.
Provide light and air. Keep the culture under a bright light for at least 16 hours a day and constantly aerate the water to keep the culture mixed and oxygenated.
Harvest regularly. After 7–10 days, the culture should be dark green and ready to harvest. Filter it through a fine mesh, store it in the fridge, and feed it to your tank in small doses.
Appreciation for Phytoplankton
Despite their tiny size, phytoplankton are among the most important organisms on Earth. They provide the majority of the oxygen people breathe, feed marine life, and even help fight climate change by absorbing carbon dioxide. Whether a scientist, a student, or an aquarium hobbyist, understanding and appreciating these microscopic wonders can deepen respect for the planet's delicate balance. Next time when taking a breath, remember—there are the phytoplankton to thank.
*Alina Bradford is a safety and security expert who has contributed to CBS, MTV, USA Today, Reader’s Digest, and more. She is currently the editorial lead at SafeWise.com.