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What role do algae play in the oxygen cycle?

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A color-coded periodic table of the elements displays each element's symbol and atomic number, with categories such as alkali metals, noble gases, halogens, transition metals, and actinoid elements distinguished by different background colors. — oxygen group element Modern version of the periodic table of the elements (printable).

Algae play a vital role in the oxygen cycle by acting as primary generators of oxygen within the biosphere. Through the process of photosynthesis, algae consume carbon dioxide and water to produce carbohydrates, releasing oxygen as a necessary by-product.12

It is estimated that algae are responsible for replacing approximately 90 percent of all oxygen used in the biosphere, with algae collectively producing up to half of the oxygen found in Earth’s atmosphere. This process is essential for maintaining the stability of atmospheric oxygen levels, which support aerobic life.314

Historically, the evolution of oxygenic photosynthesis in cyanobacteria—often referred to as blue-green algae—was a transformative event that significantly increased the oxygen content of the early atmosphere, enabling the development of oxygen-using organisms. While algae are critical to this cycle, it is important to note that under certain conditions, such as during excessive "blooms," rapid algal growth can lead to the depletion of dissolved oxygen in water, which can be harmful to aquatic life.45