What are Microalgae?

Microalgae, also known as phytoplankton, are microscopic plant-like organisms that live in water. They don’t have roots, stems, or leaves. Instead, they float freely and use sunlight to produce oxygen through photosynthesis. Microalgae fall into four main classes:

• Diatoms: found in fresh and salt water, with silica shells, and key to aquatic food webs
• Green algae: common in freshwater and marine environments, usually harmless but can signal pollution when overgrown
• Red algae: mostly marine, important to ecosystems and used in food and other products
• Blue-green algae (cyanobacteria): found in both freshwater and marine environments, and capable of forming harmful, toxin-producing blooms

Microalgae are very important for life on Earth, producing almost half of our atmospheric oxygen and acting as a key food source for aquatic animals.

However, microalgae can also be dangerous. Overgrowth of microalgae can cause harmful algal blooms to develop. Algal blooms can produce toxins, harm aquatic animals, and damage water ecosystems. So, while microalgae are helpful, we must manage them carefully to avoid problems. Read more in our guide, Discover Microalgae: The Benefits, Risks & Importance of Monitoring.