Diatoms are microscopic, single-celled algae that inhabit nearly every aquatic environment on Earth, from oceans and lakes to rivers and even damp soil. A defining characteristic of these tiny organisms is their intricate cell wall, known as a frustule, which is composed primarily of hydrated silicon dioxide, essentially glass. These unique silica structures provide protection and support for the cell. Despite their diminutive size, diatoms collectively play significant roles in planetary processes and human activities.
Foundational Role in Ecosystems
Diatoms are primary producers, generating food through photosynthesis. This process fuels aquatic ecosystems, forming the base of complex food webs. Through photosynthesis, diatoms are also producers of atmospheric oxygen. They are estimated to generate between 20% and 50% of all the oxygen produced on the planet each year.
The energy and organic material produced by diatoms are transferred throughout aquatic food webs. Zooplankton, small marine animals, graze on diatoms, subsequently becoming food for larger organisms. Diatoms also synthesize essential fatty acids, which are then passed up the food chain to larger marine life. Their abundance and productivity mean that changes in diatom populations can have cascading effects on the entire aquatic food web, impacting the health and productivity of marine and freshwater environments.
Architects of Global Cycles
Diatoms influence global biogeochemical cycles, particularly the carbon and silica cycles. Through photosynthesis, diatoms absorb carbon dioxide from the atmosphere, converting it into organic carbon. When diatoms die, their silica frustules cause them to sink to the ocean floor, carrying this sequestered carbon to the deep ocean. This process, known as the “biological carbon pump,” removes carbon dioxide from surface waters and the atmosphere, storing it in deep ocean sediments.
Their silica cell walls make diatoms central to the global silica cycle. Diatoms extract silica from the water to construct their frustules. Upon death and sinking, the silica from their frustules dissolves, returning silicon to the water column or contributing to silica deposits on the ocean floor. This continuous uptake and release of silica by diatoms helps regulate the availability of this element in marine environments, influencing the growth of other silica-dependent organisms.
Versatile Tools for Humanity
The fossilized remains of diatoms form diatomaceous earth, which has many applications. This substance is composed of porous silica frustules. Its abrasive qualities make it useful in products like polishes and toothpastes. The porous nature of diatomaceous earth also makes it an effective filtration aid in various industries, purifying liquids by trapping impurities.
Beyond industrial uses, diatomaceous earth serves as an insecticide. Its sharp edges and absorbent properties damage the waxy outer layer of insects, leading to dehydration. Diatoms are also used as bioindicators for assessing water quality. Different diatom species have varying sensitivities to environmental conditions, like pH, nutrient levels, and organic pollution. Scientists can analyze the presence, absence, or community composition of diatom species in a water body to determine its health and detect pollution.