Although microbiologists often separate unicellular algae from groups with more complex structures, we adopt a broad view. Algae are vital to the maintenance of the integrity of all ecosystems. Diatoms and other microscopic algae in the plankton of the oceans fix half to two thirds of photosynthetic carbon worldwide.
Algal photosynthesis oxygenates all waters.
Algae are the primary producers, the base of the food pyramid, of the food chains of aquatic habitats. The products of marine algae or seaweeds turn up in a huge range of everyday goods. From the late 17th century, brown seaweeds were burned for their mineral-rich ash, which yielded soda for making soap and glass, and potash for fertilizer. Chemical elements bromine and iodine were first isolated from this ash and iodine is still extracted from seaweed in Japan. Seaweeds continue in wide use as fertilizers.