Diatom

Diatoms are microscopic algae in the group Bacillariophyta. Their cell covering, called a frustule, is built from hydrated silica and typically consists of two overlapping parts. Frustule shapes and surface patterns differ widely among lineages, making diatoms both ecologically diverse and visually distinctive. Some species are solitary; others form chains or colonies. Their life cycles involve cell division and size changes, and some species can form resting stages when conditions become unfavorable.

Diatoms occur in oceans, lakes, rivers, wetlands and moist soils. As photosynthetic primary producers, they convert inorganic carbon into organic matter and support consumers in aquatic food webs. Their contribution is not uniform: local production and community composition depend on light, temperature, water movement and nutrients. Diatoms take up dissolved silicic acid to make their frustules, so silicon availability can influence their growth relative to phytoplankton that do not require silica.

When diatom cells or aggregates sink, they can transport organic matter and silica away from sunlit surface waters. This export links surface production to deeper ocean processes, although the fraction that reaches depth depends on grazing, aggregation, sinking and decomposition. Silica in frustules can dissolve and return to the water as silicic acid, where it may again become available for biological uptake. The timing and depth of dissolution affect how nutrients circulate through the water column.

The ecological influence of a diatom community cannot be inferred from cell counts alone. Research on natural assemblages found that large cells could contribute disproportionately to short-term silica production, while growth rate became more important over longer periods. Diatoms are also not a single uniform response group: species differ in size, shell properties and environmental tolerances. Claims about their global production or responses to ocean change therefore depend on the method, location and time scale being considered.