Diversity and dynamics of Antarctic marine microbial eukaryotes under manipulated environmental UV radiation

Abstract

In the light of the predicted global climate change, it is essential that the status and diversity of polar microbial communities is described and understood. In the present study, molecular tools were used to investigate the marine eukaryotic communities of Prydz Bay, Eastern Antarctica, from November 2002 to January 2003. Additionally, we conducted four series of minicosm experiments, where natural Prydz Bay communities were incubated under six different irradiation regimes, in order to investigate the effects of natural UV radiation on marine microbial eukaryotes. Denaturing gradient gel electrophoresis (DGGE) and 18S rRNA gene sequencing revealed a eukaryotic Shannon diversity index averaging 2.26 and 2.12, respectively. Phylogenetic analysis of 472 sequenced clones revealed 47 phylotypes, belonging to the Dinophyceae, Stramenopiles, Choanoflagellidae, Ciliophora, Cercozoa and Metazoa. Throughout the studied period, three communities were distinguished: a postwinter/early spring community comprising dinoflagellates, ciliates, cercozoans, stramenopiles, viridiplantae, haptophytes and metazoans; a dinoflagellate-dominated community; and a diatom-dominated community that developed after sea ice breakup. DGGE analysis showed that size fraction and time had a strong shaping effect on the community composition; however, a significant contribution of natural UV irradiance towards microeukaryotic community composition could not be detected. Overall, dinoflagellates dominated our samples and their diversity suggests that they fulfill an important role in Antarctic coastal marine ecosystems preceding ice breakup as well as between phytoplankton bloom events.

Marine photosynthetic eukaryotes in polar systems: Unveiling phytoplankton diversity and composition in Antarctic waters

“…Similarly, data on marine micro-eukar yotic diversity, applying different molecular methods with a varying resolution level, are not always equivalent. Accordingly, and keeping resolution differences in mind, diversity data suggest that the micro-eukar yotic community from Pr ydz Bay had a similar, but slightly higher diversity as compared to other diversity studies (Piquet et al 2008). Extrapolation of these results to all Antarctic waters, however, requires a much larger number of studies using approaches and methodologies that could be intrinsically comparable.…”

“…Minicosms experiments, wher e natural A n t a r c t i c m a r i n e m i c r o b i a l e u k a r y o t e communities were incubated under different ir radiation regimes, did not show major or consequent variations in community composition between dif ferent experiments, suggesting that a signifi cant contribution of natural UV irradiance towards (at least) the micro-eukaryotic community composition is not important (Piquet et al 2008). However, and in a somehow opposite way, Neale et al (2001) observe a variable but generally high sensitivity of natural phytoplankton assemblages to UV radiations, measured by biological weighting functions and exposure response cur ves for inhibition of photosynthesis by UV.…”

“…In part, this is due to one of the distinctive characteristics of Phaeocystis, its ability to form dense colonies that fl oat in the seawater. These colonies are composed by hundreds of cell forming a biofi lm-like structure, with a matrix of exopolysaccharide agglomerating the cells (Piquet et al 2008). Similarly, another group of nano-phytoplankton typically characteristic 1995, Fig.…”

“…The group that dominates is the dinofl agellates. The high diversity observed can be an indicator of the relevant role this organisms have in coastal areas of Antarctica just before ice breakup and between the development of phytoplanktonic blooms (Piquet et al 2008). In addition, microscopic data on the diversity of the microeukar yotic community gathered in another Antarctic coastal site (Fig.…”

“…Although analysis of the ef fect of these parameters using a size fractionation approach, mostly based on chlorophyll a or on DNA libraries, has been widely used (Weber & El-Sayed 1987, Stoecker & Moissan 1995, Wright et al 1996, Fiala et al 1998, Agawin et al 2002, Doolittle et al 2008, Piquet et al 2008, Wright et al 2009), the results obtained are often contradictor y or non-conclusive, indicating that more data is necessary to fulfi ll a general picture in this topic. To our knowledge there is no study were the complete size-fractions (micro-nano-and pico-phytoplankton) have been analyzed at the same time using molecular tools.…”