Sigmoid diatom
Nitzschia sigmoidea
The sigmoid diatom is a single-celled diatom characterized by its distinctive S-shaped (sigmoid) valve structure. It is among the largest benthic diatoms and is widely distributed in mesotrophic to eutrophic water bodies. The cell features a complex silicate structure with a marginal keel containing the organ of movement (raphe).
Details
Oxygen production
Produces oxygen as a byproduct of photosynthesis during the light phase.
Habitat function
Part of the epipelon (growth on mud), stabilizes surface sediment layers through mucilage production.
Nutrient uptake
High uptake of silicates for valve construction, as well as nitrates and phosphates for growth.
Food source for
Food source for benthic invertebrates (e.g., mayfly larvae) and protozoa.
Human use
Scientific use in paleolimnology and water analysis to reconstruct environmental conditions.
Ecology
Ecological role
Important primary producer in the periphyton; fixes carbon and serves as a food source for benthic invertebrates.
Natural predators
Zooplankton, small crustaceans (e.g., amphipods), snails, and other grazers of the phytobenthos.
Competitor species
Other diatoms of the genera Navicula and Gyrosigma, as well as green algae in biofilms.
Ecosystem service
Oxygen production and nutrient sequestration in aquatic systems.
Threats
Severe chemical pollution, herbicide input, and extreme acidification of water bodies.
Scientific profile
Protection & threats
Main threats
Destruction of littoral habitats, excessive herbicide load from agriculture, and extreme hydromorphological changes (bank stabilization).