Microbial communities in the surface water masses surrounding the South Shetland Islands, Antarctica

The prokaryotic and eukaryotic marine microbial communities were studied during austral summer in the South Shetland Islands (SSI) area, Antarctica. The communities were monitored by phytoplankton counts and identification in a microscope and by PCR-DGGE of small subunit ribosomal DNA. In addition data on hydrography, nutrients and chlorophyll a (Chl a) was collected. Three hydrographic regions were identified based on temperature/salinity diagrams: Weddel Sea and continental shelf water (WSSW), Antarctic Circumpolar Current water (ACCW) and waters consisting of a mix of these waters (MIXW) close to the SSI. There was an inshore to offshore gradient in temperature and salinity, low iron concentration in ACCW and a unimodal distribution of Chl a, with the highest concentration close to the SSI. The productive zone with natural iron enrichment in the area close to the SSI maintained a microbial community of both eukaryotes and prokaryotes which was significantly different from the WSSW and ACCW communities. Significant correlation between community, environmental and geographic distance matrices indicated that both historical contingencies and present environmental variables determine the community composition of both eukaryotes and prokaryotes.