PICOPHYTOPLANKTON, AS THE INDICATOR OF THE UNDERWATER LIGHT CLIMATE IN SHALLOW LAKES

Boglárka Somogyi, Centre for Ecological Research, HAS, Balaton Limnological Institute, Tihany, Hungary
Anett Kürthy, University of Debrecen, Department of Hydrobiology, Debrecen, Hungary
Balázs Németh, Centre for Ecological Research, HAS, Balaton Limnological Institute, Tihany, Hungary
Balázs Kránicz, University of Pannonia, Department of Physics and Mechatronics, Veszprém, Hungary
Lajos Vörös, Centre for Ecological Research, HAS, Balaton Limnological Institute, Tihany, Hungary

Abstract

As opposed to terrestrial plants, phototrophic communities in the water column must adapt to the spectral and intensity changes of the light field. The underwater light climate of a given water body, moreover, could change significantly due to external influences: the ‘red shift’ of the light regime is a well-known phenomenon in shallow lakes and wetlands caused mainly by the presence of brown-coloured (humic) substances or by eutrophication processes. Our aim was to characterize the underwater light climate of Hungarian lakes and to describe the main factors (humic substances, phytoplankton and inorganic suspended solids) influencing the spectral characteristics of their light field. Our second aim was to characterize how the ‘red shift’ of the underwater light climate due to external influences affects the composition and diversity of the phototrophic communities with special respect to the photoautotrophic picoplankton (<3µm). Based on the obtained results, the underwater light field of the studied lakes showed different light regime from the green waveband dominance, through the green/red predominance to the red or, in polyhumic waters, to the deep red light dominance. The picophytoplankton proved to be a good indicator of the underwater light conditions (which reflect to the water quality): as the red light became dominant, phycocyanin-rich picocyanobacteria have competitive advantage over phycoerythrin-rich ones. With the further ‘red shift’ of the light climate (deep red light dominance), however, picoeukaryotic green algae will prevail over the other two groups. The study was sponsored by the Hungarian Research Fund (OTKA K 73369).