Diatoms are microscopic, single-celled organisms that form a significant portion of the microalgae, or phytoplankton, found across the globe. They thrive in almost every aquatic environment, including the vast expanse of the oceans, freshwater lakes, rivers, and moist soils. Their massive abundance means they represent a substantial fraction of the Earth’s total biomass. Diatoms are sometimes described as the “jewels of the sea” due to their intricate structure and global importance.
Defining the Unique Silica Structure
The defining feature of diatoms is their remarkable cell wall, known as a frustule, which is a shell made of hydrated silica, essentially biogenic glass. The frustule is composed of two overlapping halves, or valves, that fit together much like a pillbox. The larger half, the epitheca, slightly overlaps the smaller half, the hypotheca, creating a protective enclosure.
Diatoms form this structure by actively drawing dissolved silicon, primarily orthosilicic acid, from the surrounding water. The silica is then polymerized inside the cell and extruded to form the geometrically patterned wall. The frustule is covered in thousands of minute pores, or areolae, arranged in species-specific, intricate patterns. These openings allow the exchange of nutrients, waste, and gases between the cell and the external aquatic environment while providing structural integrity.
The Vast Diversity of Diatom Morphology
Diatoms exhibit significant morphological diversity, with estimates suggesting the existence of over 100,000 different species. Scientists categorize this variety into two major groups based on the frustule’s symmetry and shape.
The first group, Centric diatoms, are characterized by radial symmetry, resembling a disc, cylinder, or triangle. Centric diatoms are generally non-motile and drift suspended in the open ocean. The second group is the Pennate diatoms, which display bilateral symmetry, typically appearing elongated, boat-shaped, or needle-like. Pennate diatoms often possess a slit-like groove called a raphe, through which they secrete a mucilage to facilitate gliding movement along solid surfaces. The distinct patterns etched into the frustules of both groups are routinely used by scientists to identify different species.
Diatoms as Global Ecological Powerhouses
The widespread presence of diatoms translates into an immense ecological impact, positioning them as fundamental components of the global ecosystem. As photosynthesizing organisms, diatoms function as primary producers, converting sunlight and carbon dioxide into organic compounds and oxygen. They are responsible for generating a substantial portion of the world’s breathable oxygen, with estimates ranging from 20 to 50 percent of the total produced annually.
Diatoms form the foundation of the marine food web, supporting life at every subsequent trophic level. They are intensely grazed upon by zooplankton, which in turn become food for small fish, shellfish, and large marine mammals. The energy and organic matter they generate are transferred throughout the aquatic environment, making their productivity a direct control on the health and abundance of many aquatic populations.
This productivity also regulates the Earth’s climate through the biological carbon pump. When diatoms die, they sink from the surface waters, carrying the carbon they fixed during photosynthesis toward the deep ocean floor. The dense silica frustule acts as a protective ballast, helping the organic carbon sink rapidly and efficiently before it can decompose and release carbon dioxide back into the atmosphere. This gravitational sinking effectively sequesters carbon in the deep ocean, making diatoms a significant natural mechanism for long-term carbon removal.
Practical Applications in Industry and Science
The durable silica frustules of diatoms have found several practical uses in industry and science long after the organisms have died. Over geological time, massive deposits of fossilized frustules accumulate on the ocean floor, forming a sedimentary material known as diatomaceous earth (DE). This material is harvested for its unique physical properties, primarily its high porosity and fine, abrasive texture.
Diatomaceous earth is widely employed as a filtration medium for clarifying liquids, such as water, beer, and wine. It also serves as a mild abrasive in products like toothpaste and metal polishes, and its structure makes it an effective, non-toxic mechanical insecticide for pest control. In scientific research, the long-lasting nature of the frustules provides a record of past environmental conditions. Scientists use diatoms as bioindicators, analyzing the species composition found in sediment layers to reconstruct historical water quality, temperature, and nutrient levels, aiding in paleoclimatology and environmental monitoring.