DiatomEdit
Diatoms are a large and ecologically pivotal group of photosynthetic microalgae found in almost every aquatic environment, from open oceans to rivers, lakes, and even damp soils. They belong to the phylum Bacillariophyta and are best known for their exquisite silica-based cell walls, or Frustule, which come in two halves that interlock like a delicate, glassy egg cup. This silica skeleton not only protects the cell but also bears intricate patterns that have inspired scientists across disciplines, from biology to materials science.
The frustule shells of diatoms are among the most diverse natural nanostructures, with pore lattices and ridges that vary by species and environment. This structural complexity arises from a carefully choreographed process of silica deposition guided by organic templates inside the cell. The resulting shells are often so ornate that they are preserved in the fossil record long after the organic cell has decayed, making diatoms a key source of information for researchers in paleontology and geology. The chemical composition of the frustule is nearly pure hydrated silica, and diatoms synthesize these shells with remarkable precision, a topic of ongoing study in nanotechnology and materials science. In addition to their silica framework, diatoms rely on a suite of photosynthetic pigments, including chlorophyll a, chlorophyll c, and the carotenoid fucoxanthin, which give many species their characteristic golden-brown color and optimize light harvesting in aquatic environments.
Diatoms are a central component of the phytoplankton that fuel oceanic and freshwater food webs. They convert sunlight into organic matter through photosynthesis, contributing a substantial share of global primary production and supporting a wide array of marine and freshwater life. Their siliceous remains accumulate on the seafloor and lakebeds as sediment, forming extensive deposits known as diatomaceous earth that have long been exploited for filtration, polishing, and various industrial applications. The ecological importance of diatoms extends to their role in the carbon cycle, where they contribute to the biological carbon pump by sinking organic material and silica shells to the deep ocean.
Biology and morphology
Frustule and cell design
A diatom’s defining feature is its Frustule—a rigid, two-part silica shell composed of an epitheca and a smaller hypotheca that fit together. The frustule’s elaborate pores, slits, and perforations increase surface area and influence gas exchange, nutrient uptake, and interactions with the surrounding water. Diatoms therefore exemplify how micro-scale architecture can affect macro-scale ecological processes. For those exploring the chemistry and physics of natural materials, the frustule is a prime example of biological mineralization in action. See also silica and nanotechnology for related topics.
Pigments and photosynthesis
Diatoms perform photosynthesis using a pigment complement that includes chlorophyll a, chlorophyll c, and fucoxanthin. This combination gives many diatoms their brownish coloration and enables efficient light absorption in marine and freshwater light regimes. The photosynthetic machinery integrates with cellular metabolism to drive growth and carbon fixation in dispersed, nutrient-rich as well as nutrient-poor environments.
Motility and life cycle
Some diatoms possess a raphe system that enables subtle gliding movement along substrates, which can be advantageous in navigating microhabitats and optimizing nutrient uptake. Reproduction occurs primarily by asexual division, but under certain conditions, sexual reproduction can occur, restoring cell size and maintaining genetic diversity. This life-cycle flexibility helps diatoms persist through fluctuating nutrient availability and climate conditions. For more on related cellular structures, see Raphe (diatoms) and cell division.
Ecology and distribution
Habitat and abundance
Diatoms occupy almost every aquatic niche, from sunlit surface waters to the dark depths and even saturated soils in some environments. Their proliferation is often linked to nutrient availability, light conditions, and micronutrients such as iron. As one of the most abundant groups of phytoplankton, diatoms are a foundation of aquatic ecosystems, supporting higher trophic levels and influencing microbial community dynamics.
Role in the carbon cycle
Through photosynthesis, diatoms fix carbon and contribute to the movement of carbon from the surface ocean to deeper waters as their siliceous shells sink. This process is a major component of the biological carbon pump, linking surface productivity with long-term carbon sequestration in the deep ocean. In addition to carbon, diatoms influence silica cycling, as their frustules contribute to biogenic silica budgets in marine and freshwater systems.
Taxonomy and evolution
Classification and fossil record
Diatoms form the phylum Bacillariophyta and are traditionally divided into major groups based on shell morphology, ecology, and reproductive traits. The fossil record of diatoms is rich because their silica frustules preserve well, providing insights into past oceans, climates, and biogeography. Molecular phylogenetics has refined our understanding of diatom relationships, often reshaping aspects of traditional classifications and revealing deep evolutionary splits within the group. For background on how diatoms relate to broader algal lineages, see algae and protists.
Controversies and debates
As with many groups with long scientific histories, taxonomy and classification of diatoms have seen revisions driven by new genetic data and better imaging techniques. Debates center on how to delimit genera and higher-level groups, how to treat environmentally diverse lineages, and how to interpret convergence in shell morphology. The integration of molecular data with classical morphology has been essential for resolving relationships, while some researchers stress the utility of morphology-driven classifications for field identification. The ongoing conversation exemplifies how molecular phylogenetics and traditional taxonomy can complement each other in refining our understanding of diatom diversity.
Human uses and research
Diatoms have broad applications and serve as important indicators in environmental monitoring. TheirFrustules are a natural archive of past ocean conditions, and living diatom communities reflect current nutrient regimes, salinity, and temperature. Diatomaceous earth, the fossil-rich sediment derived from diatom shells, has a wide range of uses in filtration (for beverages and water treatment), insect control, insulation, and industrial polishing. In research, diatoms are used as model organisms for studies of photosynthesis, silica biology, and aquatic ecology. See also Diatomaceous earth for more on practical applications, and bioindicator or environmental monitoring for discussions of diatoms in ecosystem assessment.