Field evidence of coupling between underwater light spectra and nano and microphytoplankton community structure in two shallow lakes

GEREA, M.; PÉREZ, G.; UNREIN, F.; SOTO CÁRDENAS, C.; MORRIS, D.; QUEIMALIÑOS, C.

Córdoba

Congreso; 16th International Congress on Photopbiology; 2014

The underwater light field is determined by the absorption and scattering of many optical active substances, among them, colored dissolved organic matter (CDOM)[1]. It has been recognized that different wavelengths could be utilized by phytoplankton due to a rich variety of photosynthetic pigments, enabling the niche differentiation and species selection in aquatic environments [2]. This chromatic adaptation has been demonstrated in picocyanobacteria [2-4], but in the nano and microphytoplankton fractions remains poorly investigated to date. An annual synchronic sampling schedule in two North Patagonian oligotrophic shallow lakes was performed to comparatively analyze the influence of CDOM over the underwater spectral light, and the consequent effects on the nano and microphytoplankton community structure. Lake Escondido (with higher CDOM concentration) showed a higher attenuation of blue and green light than Lake Morenito, being the spectral composition of underwater light field shifted towards green-yellow light. In contrast, the underwater light field in Lake Morenito was dominated by green light. These outcomes underscore the influence of CDOM over the underwater light field in oligotrophic shallow lakes. Phytoplankton composition was dominated by cryptophytes and chrysophytes in both lakes; however, the phycoerythrin containing cryptophytes prevailed in Lake Morenito and their biomass showed a positive relationship with the relative green light availability during the annual cycle. Chrysophyte biomass was comparatively more important in Lake Escondido and decreased with the relative increment of green light availability. Overall, our findings showed that chromatic adaptation could play a central role shaping nano and microphytoplankton community structure.