Chain-forming diatom
Melosira varians
Melosira varians is a widespread, chain-forming diatom found in freshwater and brackish environments. The cells are cylindrical and connected by flat end surfaces, forming long, unbranched filaments. It plays a significant role as a primary producer in aquatic ecosystems. This species is often found in nutrient-rich waters, forming brown coatings on substrates or floating as part of the phytoplankton in the water column.
Details
Oxygen production
High; actively produces oxygen during the light phase through photosynthesis.
Habitat function
Serves as a substrate for bacterial films and as a food source in benthic and pelagic zones.
Nutrient uptake
Actively absorbs nitrates, phosphates, and especially silicates for the construction of the cell wall.
Food source for
Zooplankton, benthic invertebrates, and phytophagous fish.
Human use
Used in paleolimnology as a bioindicator to reconstruct past environmental conditions.
Ecology
Ecological role
Important primary producer and base of the aquatic food web; contributes significantly to oxygen production.
Natural predators
Zooplankton (e.g., Daphnia), protozoa, snails, and various fish larvae.
Competitor species
Other diatoms (e.g., Fragilaria) and green algae when competing for light and silicates.
Ecosystem service
Oxygen production, carbon dioxide fixation, and provision of biomass for consumers.
Threats
Excessive herbicide pollution in water bodies and extreme acidification.
Scientific profile
Profile
Distinguishing features
Thick cell wall; valve surface finely punctate (often only visible under SEM); distinct auxospore formation (large, spherical cells within the chain); lacks spines at valve margins unlike Paralia.
Reproduction
Vegetative cell division (leads to size reduction); sexual reproduction via oogamy; formation of auxospores to restore maximum cell size.
Protection & threats
Status not on standard scale
Main threats
Strong acidification of water bodies; toxic pressure from herbicides; massive morphological changes in running waters (loss of shallow water zones).
Conservation measures
Reduction of diffuse nutrient inputs (phosphate/nitrate); preservation and restoration of natural river morphology and riparian zones.