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 en vironment, among the 116 taxa that we found, the most abundant were diatoms (102). The interior algal community of the sea-ice was dominated by Fragil ariopsis spp., Archeomonas areolata, and hypnozygotes of Porella glacialis. In the algal mat at the deeper layer of the ice, however, diatoms showed h igher density. Photoautotrophic picoplankton was also present and red-fluor escing cells, small eukaryotes and phycocyanin-rich cyanobacteria prevailed over phycoerythrin-rich cyanobacteria. Besides these data, ultrastructural , physiological and biomolecular surveys on three Antarctic sea water micro algae, of which only Koliella antarctica was known, were also carried out. The 18S rDNA gene sequences of K. antarctica and other closely related spec ies allowed us to verify that the Koliella genus belongs to Trebouxiophycea e, 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 rscribed species of the Southern Ocean. Pyramimonas sp., found in Terra Nov a Bay during the austral summer 1998-99, carried trichocysts. Moreover, K. antartica, like Heterococcus sp., showed great ability to live both in fres h water and at different salinities.