Distribution scheme of the three ciliate species Askenasia chlorelligera, Balanion planctonicum and Urotricha cf. castalia prevailing in an alpine lake throughout the ice-free summer months (June/July through October/November).

Heterotrophic ciliate probably accumulating UV-sunscreens (MAAs) through algal food.

Voracious heterotrophic ciliate dependent on high algal food concentrations. Near the lake bottom not only algae are abundant but UV radiation intensity is lowest, thus the UV-sensitive B. planctonicum remains in the greatest depths.

Mixotrophic ciliate that receives UV-sunscreens (MAAs) from its symbiotic algae allowing the species to exploit all water depths in the lake.

Copopod that potentially predates on ciliates. To avoid ingestion, rapid escape jumps are performed by the ciliates.

This alpine lake is highly transparent to even UV-B radiation that can reach the lake bottom (K 320 nm = 0.33 m-1, Z1% = 14.0 m).

Assumption: algal food quality and quantity appears to be higher in deeper areas and B. planctonicum rules out U. cf. castalia that is mainly detected in the surface layers. However, U. cf. castalia is obviously better adapted to high incident solar radiation.

Ciliate plankton in an alpine lake