Phytoplankton communities in Patagonian and Antarctic lakes: a latitudinal study. International Association of Phytoplankton Taxonomy and Ecology

IZAGUIRRE, IRINA; SAAD, JUAN FRANCISCO; SCHIAFFINO, ROMINA; VINOCUR, ALICIA; TELL, GUILLERMO

kastoria

Workshop; 17th Workshop of the International Association of Phytoplankton; 2014

IAP (International Association of Phytoplankton)

In protist biogeography two main models are currently discussed: the ?ubiquity model? that postulates that everything is everywhere but the environment selects, and the ?moderate endemicity model?, which poses that a third of free living protists would present a restricted geographical distribution. We investigated the structure of phytoplankton in 62 freshwater environments (including deep lakes, shallow lakes and ponds) across a latitudinal gradient from Austral Patagonia (Argentina) to Antarctica. The environments were sampled in late spring (Patagonia) and in the austral summer (Antarctica) throughout different field campaigns from 2004 to 2012. The following hypotheses were tested: 1) The species richness of phytoplankton in lakes decreased with increasing latitude. 2) The phytoplankton structure is influenced by both geographical and environmental factors. We also analysed the predominant algal trophic strategies (mostly autotrophic vs mixotrophic) in lakes with contrasting trophic states. The phytoplankton structure was analysed using a polyphasetic approach (species diversity, functional diversity and dominant molecular diversity); the species diversity and eveness were estimated. The results of the multivariate analysis (Redundancy Analysis) showed that the phytoplankton functional groups can be well predicted from the environmental variables: the most important and significant variables were temperature and those related with the trophic state of the lakes (mainly nutrients). Molecular DGGE analysis (denaturing gradient gel electrophoresis) resulted in 82 different DGGE band positions, which represent the total dominant eukaryotic nanoplankton richness in the studied lakes. We found a significant decreasing pattern in phytoplankton richness (microscopical analyses) and in the dominant eukaryotic nanoplankton richness (DGGE) with latitude. On the other hand, we observed that the ratio autotrophs/mixotrophs increases towards higher trophic states. Our results support the hypothesis of biogeographic patterns in phytoplankton, indicating that both spatial and environmental factors control the community structure. Analyses based on morphological species diversity and dominant molecular diversity showed comparable patterns.