ORIGINAL PAPER A comparison of epiphytic diatom communities on Plocamium cartilagineum (Plocamiales, Florideophyceae) from two Antarctic areas Roksana Majewska • Piotr Kuklinski • Piotr Balazy • Nair Sumie Yokoya • Aline Paternostro Martins • Mario De Stefano Received: 20 March 2014 / Revised: 4 September 2014 / Accepted: 7 September 2014 Ó Springer-Verlag Berlin Heidelberg 2014 Abstract Our understanding of diatoms, one of the most important Antarctic primary producers, is based mostly on investigations of plankton, sea-ice, and sediment samples. Herein, we contribute to the limited research devoted to benthic Antarctic diatoms by presenting a study on epi- phytic diatom communities sampled in two remote Ant- arctic regions: Admiralty Bay (maritime Antarctica, Antarctic Peninsula) and Terra Nova Bay (Ross Sea). Recent studies have demonstrated that the most critical factor for the local epiphytic diatom communities was the nature of the substrate. In order to eliminate this factor so we could evaluate other potential controls, we sampled epiphytic diatoms from only one substrate that is common to both regions: the macroalgae Plocamium cartilagineum (L.) Dixon. Thalli of P. cartilagineum and their associated microalgal community was collected in January 2011 (Admiralty Bay) and 2012 (Terra Nova Bay) from a water depth of 5–25 m. Dehydrated macroalgal pieces were placed on stubs and sputter-coated, which allowed obser- vation of diatoms attached to the substrate in their original position using scanning electron microscopy. A total of 72 taxa were observed, of which 31 taxa were common to both regions. Cell abundance and diatom growth form domi- nance were significantly different in Admiralty Bay and Terra Nova Bay samples. Total diatom abundance was higher in Admiralty Bay samples, dominated by adnate diatoms (Cocconeis spp.), but the number of taxa found as well as the values of ecological indices were higher for samples from the Ross Sea, where motile forms were dominant (Navicula spp.). Our results suggest that Ant- arctic shallow-water benthic habitats may present a high degree of microniche heterogeneity and highlight the need of fine-scale analyses in microbial studies. We also suggest grazers as a factor that contributes greatly to the observed differences. Keywords Antarctic diatoms Á Epiphytes Á Grazing Á Growth form Á Plocamium cartilagineum Á SEM Introduction After decades of extensive research in the Antarctic, it has become clear that throughout much of this region, eco- system processes are dominated by microscopic organisms (Vincent 2000; Stanish et al. 2013; Wilkins et al. 2013). In the highly productive coastal region of Antarctica they have an important role in biomass and energy flow (Ne- dwell et al. 1993; Archer et al. 1996; Cattaneo-Vietti et al. 1999; Vincent 2004; Bowman 2013; Wilkins et al. 2013). Although our current understanding of Southern Ocean diatoms is based mainly on studies of plankton and sea-ice samples, and sediment cores, our knowledge of epiphytic Electronic supplementary material The online version of this article (doi:10.1007/s00300-014-1578-7) contains supplementary material, which is available to authorized users. R. Majewska (&) Á M. De Stefano Second University of Naples, Caserta, Italy e-mail: roksana.majewska@unina2.it P. Kuklinski Á P. Balazy Institute of Oceanology, Polish Academy of Sciences, Sopot, Poland N. S. Yokoya Institute of Botany, Centre for Research in Phycology, Sa ˜o Paulo, Brazil A. Paternostro Martins Institute of Chemistry, University of Sao Paolo, Sa ˜o Paulo, Brazil 123 Polar Biol DOI 10.1007/s00300-014-1578-7