Underwater Measurements of Transmitted Light Spectra in Stratified Reservoirs of the White Sea Coast as a Key to the Understanding of Pigment Composition of Phototrophs in the Chemocline Zone

Abstract

Measurements of the spectral composition of light at the boundary of the photic zone in seven coastal reservoirs, which are isolated from the sea to varying degrees, as well as in the marine water area and in a freshwater lake showed that in marine and brackish reservoirs, mainly green light reaches it; in lakes with a fresh upper layer it is orange, red and far-red. In meromictic reservoirs, the photic zone was limited by a colored layer of water with a massive development of phototrophic microorganisms. Their pigment composition is in good agreement with the spectral composition of transmitted light. The marine bays and lagoons were dominated by taxa with red pigments: cryptophytic algae with phycoerythrin-545, purple sulfur bacteria with okenone carotenoid, brown green sulfur bacteria with isorenieratene and bacteriochlorophyll e. In lakes with fresh upper water, unicellular algae and green sulfur bacteria with chlorobactene and bacteriochlorophyll d developed. The spectral range can serve as a selective factor that determines the composition of a community of phototrophs with structurally different antennas and similar light absorption spectra.