Sub-ice colonial <i>Melosira arctica</i> in Arctic first-year ice

As one of the three main algal communities associated with polar sea ice, the occurrence of a sub-ice community has been recorded during a May 2012 field campaign conducted in the central Canadian High Arctic around Cornwallis Island, Nunavut. The sub-ice community was only observed once at the nearshore station in Wellington Channel (water depth: 85 m; ice thickness: 1.3 m; snow depth:<4 cm), forming short strands< 10-15 cm in length. The community was dominated by the northern cold water centric diatom, Melosira arctica Dickie, which formed very dense aggregates of several parallel, vertically aligned chains of cells, held tightly together by a secretion of mucilage from the rimoportulae on the valve face within the limit of the carina. In addition, three epiphytic diatom taxa were present, Chaetoceros sp., Synedropsis hyperborea (Grunow) Hasle, Medlin & Syvertsen and Pseudogomphonema arcticum (Grunow) Medlin. Surprisingly, and in addition to these epiphytes, some raphe-bearing diatoms were also part of this sub-ice community, gliding over the colonial filamentous cells of M. arctica. © 2014 © 2014 The International Society for Diatom Research.