Limnetica 32

Maritime Antarctica shows less severe weather conditions than continental Antarctica, thereby allowing an important thaw process during the austral summer that increases both light availability for primary production and the inputs of nutrients and organic matter through run-off. Thus, a rapid development of certain phytoplankton groups is favoured at the beginning of the austral summer as a direct effect of the higher availability of light and nutrients after the ice thaw. Inputs of allochthonous organic matter from microbial mats and moss carpets distributed across the catchment also enhance the abundance of heterotrophic bacterioplankton. Indeed, the bacterioplankton abundance and the availability of organic matter are correlated for each studied depth, revealing a possible differential use of the organic matter. Additionally, the availability and dynamics of different types of dissolved organic matter (autochthonous and allochthonous) may influence the diversity and abundance of the different bacterioplankton groups along the water column and throughout the summer, with a relative abundance of each group that differs between the surface and bottom waters. The study of DGGE patterns reveals the existence of changes in the abundance of different bacterial taxa during the summer and the different relative importance of each bacterial group at each depth. This result can also be related to the organic matter dynamics during the austral summer, as evidenced by the correlation between the concentration of chromophoric dissolved organic matter (CDOM) and abundance of bacterioplankton at each depth. Therefore, the regional temperature regime, which allows ice thaw of the lakes and their catchments during summer, plays a key role in the onset of biological processes and the length of the productive season throughout the austral summer.