Phytoplankton communities in relation to trophic status in lakes from Hope Bay (Antarctic Peninsula)

Nine lakes and ponds of Hope Bay (Antarctic Peninsula), with different trophic status were surveyed during four summer periods between 1991 and 1996. Some limnological features and the structure of their algal assemblages were strongly influenced by the eutrophication caused by sea-birds activity in their areas. Such differences among lakes were evidenced by the results of Principal Component Analyses, based on both physico-chemical and phytoplankton data. Oligotrophic lakes showed a scarce phytoplankton, commonly dominated by small flagellated Chrysophyceae, and a well developed phytobenthos. Water bodies enriched by ornithogenic nutrients revealed an abundant phytoplankton usually dominated by Chlorophyceae (Volvocales) and planktonic Cyanobacteria. A study on one particular lake showed that summer changes in the phytoplankton community were mainly affected by physical phenomena such as variation in light intensity, and thawing, mixing and freezing processes.