Fragilariopsis and Pseudo-nitzschia species (Bacillariophyceae) in the Antarctic and Arctic: distribution, morphology and genetic variation

Summary

The pennate diatom genera Pseudo-nitzschia and Fragilariopsis are common components of the phytoplankton community in Antarctic and Arctic waters and are important primary producers. Cryptic and pseudo-cryptic species of these genera occur, and electron microscopy and molecular methods are here required for a precise species identification. The aim of this study is to determine which species of Pseudo-nitzschia and Fragilariopsis that are present in different polar water masses, which species appear to be bipolar, and do strains from Antarctic and Arctic waters differ morphologically and genetically. The material from the Atlantic sector of the Southern Ocean was collected during a cruise with R/V G.O. Sars during summer 2008 along a N-S transect at 15°E between 45-67°S, while the material from the Arctic was collected along a E-W transect from Svalbard into Fram Strait summer 2009 with R/V Lance. Water samples, net hauls, and hydrographical data were collected and algal cultures started onboard on both cruises. More than 50 diatom strains from Antarctic and about 20 from Arctic waters have been established. Preserved and live algal material have been examined in the light and electron microscope, and 8 different Fragilariopsis species were observed from one Antarctic station. The cultured strains have been identified to species by electron microscopy (SEM and TEM) and analysed genetically, using coding (LSU) and non-coding (ITS) ribosomal DNA sequences as markers. Genetic examination of Fragilariopsis from the Antarctic shows that ITS, but not LSU rDNA can discriminate between closely related species. Our ITS rDNA sequence data suggests two genotypes in culture of the F. cylindrus and F. nana ‘species-complex’, differing from those previously reported. Our results will link morphology with genetic signature and geographic origin, and will give new knowledge on their genetic variability and distribution.