Ecological, physiological and biomolecular surveys on microalgae from Ross Sea (Antarctica)

Results of analyses on pico, nano- and microphytoplankton from the sea-ice of Terra Nova Bay, during austral summer 1995- 96, are reported. In this environment, among the 116 taxa that we found, the most abundant were diatoms (102). The interior algal community of the sea-ice was dominated by Fragilariopsisspp., Arcbeomonas areolata, and hypnozygotes of Porella glacialis. In the algal mat at the deeper layer of the ice, however, diatoms showed higher density. Photoautotrophic picoplankton was also present and red-fluorescing cells, small eukaryotes and phyco- cyanin-rich cyanobacteria prevailed over phycoerythrin-rich cyanobacteria. Besides these data, ultrastructural, physiological and biomolecular surveys on three Antarctic sea water microal- gae, of which only Koliellaantarctica was known, were also car- ried out. The 18S rDNA gene sequences of K. antarctica and oth- er closely related species allowed us to verify that the Koliella genus belongs to Trebouxiophyceae, while as regards the other two taxa, one of them was found to belong to the Heterococcus and the other to the Pyramimonas genus. They might be unde- scribed species of the Southern Ocean. Pyramimonas sp., found in Terra Nova Bay during the austral summer 1998-99, carried tri- chocysts. Moreover, K. antartica, like Heterococcus sp., showed great ability to live both in fresh water and at different salinities.