Needle diatom
Synedra acus
The needle diatom is a unicellular primary producer characterized by a strongly elongated, siliceous cell wall (frustule). It lives predominantly planktonically in stagnant and slow-flowing freshwater bodies. The cells can occur individually or form short, star-shaped colonies. As a diatom, it plays an essential role in the silicate cycle of aquatic ecosystems.
Details
Oxygen production
Produces oxygen as a byproduct of photosynthesis during daylight hours.
Habitat function
Part of the suspended biomass that feeds energy into the pelagic food web.
Nutrient uptake
Actively absorbs silicates, phosphates, and nitrates from the water.
Food source for
Zooplankton, small crustaceans, and fish larvae.
Human use
Used in paleolimnology to reconstruct past environmental conditions.
Ecology
Ecological role
Important primary producer; forms the nutritional basis for filter-feeding zooplankton.
Natural predators
Zooplankton such as daphnia, rotifers, and various ciliates.
Competitor species
Other phytoplankton species such as green algae or cyanobacteria, especially during nutrient competition.
Ecosystem service
Oxygen production and carbon dioxide fixation in inland waters.
Threats
Excessive eutrophication and chemical pollution of water bodies.
Scientific profile
Profile
Distinguishing features
Possesses a heavily silicified frustule. Characteristic is the extremely high length-to-width ratio (length 100-500 µm with only 2-6 µm width). The central area is usually distinct, square to rectangular, and reaches the margins. Striation (striae) is fine (approx. 12-18 striae per 10 µm). Taxonomically often listed under the name Ulnaria acus.
Reproduction
Asexual reproduction by cell division, where daughter cells each form a new hypotheca (leading to size reduction). Sexual reproduction via auxospore formation to restore the original cell size.
Protection & threats
Status not on standard scale
Main threats
Extreme eutrophication (hypertrophication) leading to light limitation by cyanobacterial blooms; silicate deficiency due to anthropogenic interference in the water cycle.
Conservation measures
Preservation and restoration of natural nutrient cycles; reduction of phosphate and nitrogen inputs to avoid hypertrophic conditions.