Slender diatom
Fragilaria gracilis
The slender diatom (Fragilaria gracilis) is a widespread species of diatom found primarily in stagnant and slow-flowing freshwater bodies. It is characterized by its extremely narrow, needle-like cells, which often form loose star-shaped or zigzag colonies. As a photoautotrophic organism, it plays a fundamental role as a primary producer in aquatic food webs.
Details
Oxygen production
High; contributes significantly to oxygen saturation in the euphotic zone.
Habitat function
As part of the periphyton, it also colonizes the surfaces of aquatic plants and stones.
Nutrient uptake
Actively takes up dissolved phosphate, nitrate, and especially silicate from the water.
Food source for
Primary food source for herbivorous zooplankton and benthic grazers.
Human use
Important reference species in biological water monitoring according to the EU Water Framework Directive.
Ecology
Ecological role
Base of the aquatic food web; fixes carbon and produces oxygen; serves as a food source for zooplankton.
Natural predators
Zooplankton (e.g., Daphnia and copepods), ciliates, and filter-feeding macroinvertebrates.
Competitor species
Other planktonic diatoms (e.g., Asterionella formosa) and green algae competing for light and silicate.
Ecosystem service
Oxygen production, primary production, and an important part of the biological carbon pump in lakes.
Threats
Excessive nutrient input (eutrophication), chemical pollution, and the warming of surface waters.
Scientific profile
Profile
Distinguishing features
Very narrow valve width (1.5–3 µm), extremely fine transapical striae (22–28 in 10 µm) that are difficult to resolve with light microscopy. Central area is absent or only minimally developed on one side.
Reproduction
Asexual by vegetative cell division with successive size reduction; sexual via auxospore formation to restore initial cell size.