Phytoplankton: An Invisible Army Saving the Planet

When we talk about protecting Earth, we think of forests, urban greening, and reducing emissions. But there is a hero we almost never remember, though he does most of the work for us. He is invisible to the eye, he lives in the oceans, and his population is counted in billions in every drop of water. This is phytoplankton. Without it, there would be no life on land, no familiar climate, and even no air we breathe. It produces 50 to 80% of the oxygen on the planet. It absorbs carbon dioxide like a giant filter. And it is under threat because we do not notice how we are destroying its environment.

Who are these invisibles

Phytoplankton is microscopical algae and cyanobacteria that inhabit the upper, illuminated layer of the ocean. They drift with currents, cannot actively swim, but their role in the ecosystem is colossal. Like plants on land, they use sunlight, carbon dioxide, and mineral substances for photosynthesis. In the process, they release oxygen and create organic matter that is the basis for the entire marine food chain — from zooplankton to whales.

These organisms are incredibly diverse: from single-celled diatoms to colonial forms that can be seen with the naked eye as a green film on the surface of the water. Their sizes range from a micron to several millimeters, but their total biomass is comparable to that of all terrestrial plants. They are the foundation of oceanic life and one of the main regulators of the climate.

Oxygen shield of the planet

We often hear the phrase “lungs of the planet” in relation to the Amazon rainforest or Siberian taiga. But in fact, the main lungs of Earth are the oceans. And it is exactly phytoplankton that provides most of this breathing. Scientists have calculated that every second breath you take is owed to these microscopic organisms. They not only produce oxygen but also absorb carbon dioxide that we emit into the atmosphere by burning fossil fuels.

The mechanism is called “biological pump”. Phytoplankton takes carbon from the atmosphere and converts it into organic compounds. Part of this carbon, when the algae die, sinks to the bottom of the ocean and remains there for millennia. In this way, the ocean sequesters a huge amount of carbon, mitigating the effects of global warming. If phytoplankton suddenly disappeared, the concentration of CO₂ in the atmosphere would increase so much that the climate would become completely different — and most likely, unsuitable for life in its current form.

Threats to phytoplankton: from warming to pollution

Ironically, the same carbon dioxide that phytoplankton absorbs is one of the main threats to its existence. Rising ocean temperatures cause the stratification of water masses: warmer water, less dense, lingers at the surface and does not mix with deep, nutrient-rich water. And phytoplankton needs not only light and CO₂ but also minerals — nitrates, phosphates, iron. Without them, it cannot reproduce. Therefore, warming has led to a decrease in the productivity of phytoplankton in some regions by 10–20% in recent decades.

In addition, ocean acidification caused by the absorption of CO₂ threatens species with calcareous shells, such as coccolithophores and pteropods. Their shells simply do not form in acidic water. This destroys the entire food chain. And pollution with microplastics and chemicals also does not go unnoticed: toxins accumulate in the cells of phytoplankton, passing on further along the chain — to fish, marine birds, and whales.

Protecting phytoplankton: protecting ourselves

What can we do? First, reduce CO₂ emissions, switch to renewable energy sources. Second, reduce plastic and chemical effluents in the ocean. Third, create marine protected areas where industrial activity is limited. Fourth, support scientific research that will help understand how phytoplankton responds to changes and how we can help it adapt.

This is a difficult task, but it is achievable. Every decision we make — from choosing transportation to our attitude towards waste — affects the ocean, and thus, phytoplankton. Protecting this invisible army is not an abstract ecological slogan. It is a question of our own survival. As long as phytoplankton lives, we live. And we should remember this every time we look at the sea.

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