Star green alga
Pediastrum spp.
The star green alga (Pediastrum) is a genus of green algae that forms flat, radially symmetrical colonies. These colonies, known as coenobia, consist of a fixed number of cells often arranged in a star-like pattern with characteristic processes on the peripheral cells. They are distributed worldwide in freshwater ecosystems, particularly in mesotrophic to eutrophic stagnant water bodies.
Details
Oxygen production
Produces significant amounts of oxygen in the euphotic zone.
Habitat function
Provides microhabitats for small epibionts and serves as a food base.
Nutrient uptake
Efficient uptake of phosphates and nitrates from the water column.
Food source for
Daphnia, copepods, rotifers, and fish larvae.
Human use
Used in paleolimnology to reconstruct past environmental conditions in lake sediments.
Ecology
Ecological role
Important primary producer in the aquatic pelagic zone; base of the food chain for zooplankton.
Natural predators
Filter-feeding zooplankton such as Daphnia, rotifers, and small non-predatory fish.
Competitor species
Other phytoplankton species such as cyanobacteria or other green algae (e.g., Scenedesmus).
Ecosystem service
Oxygen production through photosynthesis and fixation of atmospheric carbon.
Threats
Excessive eutrophication (blooms of other species), chemical water pollution, and herbicides.
Scientific profile
Profile
Distinguishing features
Characteristic star-shaped coenobia; cell walls contain algaenan (highly resistant polymer), making them fossilizable; lack of a mucilaginous sheath compared to similar genera.
Reproduction
Asexual via zoospores forming a new coenobium within a vesicle; sexual via isogamy (fusion of biflagellate gametes).
Protection & threats
Status not on standard scale
Main threats
Extreme acidification of water bodies and chemical contamination by herbicides.
Conservation measures
Maintenance of water quality; reduction of diffuse nutrient inputs to prevent hypertrophy.