Take a deep breath. And then another. One of those breaths came from trees. But the source of the other breath might surprise you.
“Around 50 percent of the oxygen we breathe comes from phytoplankton,” said Brenda María Soler-Figueroa, a marine biologist at the Smithsonian Environmental Research Center.
Phytoplankton are tiny plants that live on the surface of oceans and lakes. Each one is invisible to the naked eye, but when they gather together in great numbers, they can turn a body of water red, green or milky white based on which variety is present.
“They come in different sizes and shapes,” Soler-Figueroa said. “For example, some look like a bowl with two tails, or they may have an elongated oval shape, or even a forklike shape. Some have spiny structures, and others have structures that look like a crown.”
Like trees and other plants, phytoplankton can absorb sunlight and turn it into energy through a process called photosynthesis. Fortunately for us, photosynthesis also creates oxygen as a waste product, which the phytoplankton and plants expel — just like how humans and other animals produce carbon dioxide when we exhale.
Although phytoplankton are tiny, there are a lot of them out there. There can be thousands of phytoplankton in a single drop of water, Soler-Figueroa said. Now imagine an ocean full of them releasing little invisible puffs of oxygen all day long.
Of course, providing the air we breathe isn’t the only important thing phytoplankton do. They also serve as the base of marine food webs. Many kinds of animals eat phytoplankton, including whales, jellyfish, shrimp, and small fish.
“Although they are very important for the environment and the aquatic ecosystems, phytoplankton can also do harm to the environment,” Soler-Figueroa said.
For instance, when there are too many nutrients in the water, often as a result of farmers’ fertilizers getting washed out into the ocean, phytoplankton can multiply rapidly and create what’s known as an algal bloom.
The problem with algal blooms, said Soler-Figueroa, is that many of these species produce toxins that can be deadly to other ocean life. In great numbers, phytoplankton can also cause a chain reaction that uses up all of the oxygen in the water and creates what marine biologists call “dead zones,” where most can’t survive.
“So they’re important, but as with all life, there needs to be a balance,” Soler-Figueroa said.
Perhaps the coolest thing about phytoplankton, apart from providing the oxygen that we breathe, is that some of them can glow.
In Puerto Rico, which Soler-Figueroa calls home, you can kayak at night and watch as the water lights up with tiny blue and green fireworks around your paddle. Phytoplankton use the ability to create light, known as bioluminescence, as a way to distract and escape from predators.
“You can describe it, but it’s not the same as seeing it,” said Soler-Figueroa. “It’s pretty amazing.”
Correction: An earlier version of this story referred to phytoplankton as creatures. They are plants. The story has been updated.