Star-shaped diatom
Asterionella formosa
Asterionella formosa is a widely distributed freshwater diatom commonly found in the phytoplankton of lakes and reservoirs. It is characterized by the formation of star-shaped colonies where individual cells are joined at one end by mucilage pads. This species plays a significant role in the primary production of aquatic ecosystems, especially during spring blooms, serving as a vital food source for zooplankton.
Details
Oxygen production
High during bloom phases in spring and autumn.
Habitat function
Forms the base of the pelagic food web.
Nutrient uptake
High demand for silicate for the construction of its frustules (silica shells).
Food source for
Primary food source for many filter-feeding zooplankton.
Human use
Used in paleolimnology to reconstruct past environmental conditions.
Ecology
Ecological role
Major primary producer; converts inorganic carbon into organic biomass and releases oxygen.
Natural predators
Zooplankton (e.g., Daphnia, rotifers), parasitic fungi (chytrids).
Competitor species
Other diatoms (e.g., Fragilaria) and green algae during nutrient competition.
Ecosystem service
Oxygen production and carbon sequestration in aquatic systems.
Threats
Climate change (warming of lakes), herbicide runoff, extreme eutrophication.
Scientific profile
Profile
Distinguishing features
Araphid diatom (lacks a raphe); stellate colony arrangement; linear in girdle view with capitate ends; valve surface with fine transapical striae (approx. 25-30 in 10 µm).
Reproduction
Mainly asexual through vegetative cell division; sexual reproduction (oogamy) is extremely rare and leads to auxospore formation to restore cell size.
Protection & threats
Status not on standard scale
Main threats
Climate change (increased lake stratification), silica depletion due to anthropogenic factors, herbicide runoff.
Conservation measures
Nutrient input management (eutrophication control), protection of water quality according to the WFD.