Star alga
Pediastrum
The star alga belongs to the genus Pediastrum and is a widespread planktonic green alga in freshwater habitats. It forms characteristic, flat, disc-shaped colonies (coenobia) that often appear star-shaped or serrated. The number of cells per colony is usually a power of two (e.g., 8, 16, 32). These algae are important primary producers in stagnant waters and are characterized by their robust cell walls.
Details
Oxygen production
Actively produces oxygen during the light phase through photosynthesis.
Habitat function
Provides surfaces for colonization by bacteria (biofilms) in the pelagic zone.
Nutrient uptake
Absorbs phosphates and nitrates directly from the water column.
Food source for
Daphnia, rotifers, and other herbivorous microorganisms.
Human use
Scientific research in limnology and paleoecology; no direct economic use.
Ecology
Ecological role
Important primary producer in freshwater plankton; forms the nutritional basis for filter-feeding zooplankton.
Natural predators
Zooplankton such as rotifers (Rotatoria) and small crustaceans (e.g., Daphnia).
Competitor species
Other phytoplankton species such as Scenedesmus or various diatoms.
Ecosystem service
Oxygen production and carbon fixation in limnic ecosystems.
Threats
Excessive herbicide levels in water bodies; extreme acidification.
Scientific profile
Profile
Distinguishing features
Characteristic star-shaped or disc-shaped coenobia; cell walls often contain algaenan (highly resistant biopolymer), making them fossilizable; species-specific number and shape of marginal processes.
Reproduction
Asexual by formation of zoospores that arrange themselves into a new autocolony within a vesicle; sexual by isogamy (fusion of biflagellate gametes).
Protection & threats
Main threats
Herbicide inputs from agriculture, extreme acidification (pH < 5), massive pesticide pollution.
Conservation measures
Reduction of diffuse nutrient inputs; protection of riparian buffer strips for pesticide retention; maintenance of natural water dynamics.