Seasonal Variation of the Calcifying Green Alga Phacotus lenticularis (Ehrenb.) Stein in Water Bodies under Human Influence (Mid-Western Poland)

The unicellular flagellates of the genus Phacotus, which form a solid calcite lorica by extracellular precipitation of calcium carbonate are some of the nanoplankters quite frequently occurring in hardwater ecosystems of the temperate zone. The aim of this study was to describe seasonal changes of Phacotus lenticularis populations in several types of water bodies (a glacial lake, small and shallow ponds, and a lowland river) in relation to some environmental parameters. All the water bodies are subject to multiple human pressure: recreation, fishing, agriculture, and urbanization. P. lenticularis individuals preserved in Lugol’s solution were counted under an inverted microscope (after sedimentation in 14 or 9 mL chambers), including both empty and filled loricae. Its populations differed both between seasons and between waters. High P. lenticularis abundance was mainly limited to the summer months. It was observed at temperatures above 19 °C and pH values above 7.8, in water characterized by quite high electrolytic conductivity (>500 μS cm⁻¹). Statistical analysis reveals two significant relationships between physicochemical parameters and the abundance of P. lenticularis. This suggests that in the investigated waters the biotic factors and processes are probably more important regulators of changes in the density of its population than nutrients.