Diatom (dwarf form)
Bacillariophyceae (small morphotypes)
Dwarf-form diatoms describe small representatives of the Bacillariophyceae, usually measuring less than 15-20 micrometers. These forms often result from the successive reduction of silica valves during asexual reproduction (MacDonald-Pfitzer rule). They are ecologically significant as primary producers and oxygen providers in both lentic and lotic waters. Due to their small size, they often require specialized microscopic techniques for exact identification or are treated as a collective group in water quality monitoring.
Details
Oxygen production
High; diatoms are responsible for a significant portion of global oxygen production.
Habitat function
Provides the nutritional basis for primary consumers in the pelagic zone.
Nutrient uptake
Efficient uptake of dissolved silicate, nitrate, and phosphate directly from the water column.
Food source for
Zooplankton, filter feeders, and juvenile fish.
Human use
Use of fossil deposits (diatomaceous earth) in filters, abrasives, and as insulating material.
Ecology
Ecological role
Important primary producers that sequester CO2 and form the base of the pelagic food web.
Natural predators
Zooplankton (e.g., rotifers, cladocerans), herbivorous protozoa, and small fish larvae.
Competitor species
Other phytoplankton groups such as green algae or cyanobacteria, especially during silica depletion.
Ecosystem service
Oxygen production through photosynthesis and contribution to the global carbon and silicon cycles.
Threats
Water pollution, herbicide input, and climate-change-induced changes in water stratification.
Scientific profile
Profile
Distinguishing features
Siliceous frustule consisting of two valves (epitheca/hypotheca). Small morphotypes are characterized by a diameter < 20 µm. Identification often requires electron microscopy to visualize striae (rows of pores) and fultoportulae.
Reproduction
Asexual cell division (binary fission), leading to a successive reduction in cell size; restoration of maximum size through sexual formation of auxospores.
Protection & threats
Main threats
Silica depletion due to dam construction (silica trapping), herbicide inputs from agriculture, extreme summer heatwaves.
Conservation measures
Reduction of diffuse nutrient inputs (P-elimination), restoration of riparian zones for input buffering, maintaining connectivity for silica transport.