| Summary: | Species diversity of microorganisms inhabiting Antarctic waters seems to be relatively low. However, they metabolic flexibility is unusually high, making them fundamental to the Antarctic ecosystem functioning. In polar waters, microalgal communities associated to macroalgae and invertebrates exhibit rates of primary production comparable or even higher than those of phytoplanktonic ones. These benthic microalgal communities are for the most part represented by diatoms. Despite to their crucial ecological role in the trophic chain, the biodiversity of antarctic epiphytic diatoms is poorly studied and greatly underestimated. In the present study, the diversity of epiphytic diatom communities from coastal waters of Terra Nova Bay (Ross Sea, Antarctic continent) has been investigated and described for the first time. Samplings were made during the Italian Antarctic expeditions in the years: 1989/90, 1990/91, 1993/94, 1994/95, 1998/1999, 2000/01, 2001/02 and 2004/05. Thalli of Iridaea cordata, Phyllophora antarctica and Plocamium cartilagineum were collected by scuba diver during the austral summer. Collections were made from different depths at five sampling sites localized along the shore and fixed with formaldehyde. To observe diatom communities originally settled on the macroalgal host preserved thalli were cut, dehydrated, placed on a stub and sputter coated with thin layer of gold. Taxonomical identification and counting of diatom cells has been carried out by scanning electron microscope. According to our results biomass appears to be inversely related to the diversity. The diatom community composition varied depending on the sampling site as well as on the morphology of the macroalgal host. Some differences could be observed also along a depth gradient. In terms of growth form in most cases adnate (e.g. Cocconeis, Amphora) and mobile forms (e.g. Navicula, Nitzschia) dominated. Erect diatom taxa tended to be associated with animal macrofouling species.
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