POSSIBLE SYMBIOSIS OF BERKELEYA ADELIENSIS MEDLIN, SYNEDROPSIS FRAGILIS (MANGUIN) HASLE ET AL. AND NITZSCHIA LECOINTEI VAN HEURCK (BACILLARIOPHYTA) ASSOCIATED WITH LAND-FAST ICE IN ADÉLIE LAND, ANTARCTICA

Abstract

Berkeleya adeliensis Medlin is a tube-dwelling diatom commonly associated with the bottom level of land-fast ice and the underlying unconsolidated layer or “platelet ice”, in Antarctica, particularly in Adélie Land. This taxon often accounting for a great proportion of the biomass (up to 10⁸ cells 1⁻¹) exhibits a colonial life habit. Cells are grouped in large mucilaginous tubes, sometimes centimetric, which show a polarity: new cells are closely grouped toward one pole of the tube, whereas at the other pole cells are scarce, loosely arranged and with a large proportion of degraded and empty cells. Small pennate diatoms belonging to Synedropsis fragilis (Manguin) Hasle, Syversten & Medlin live as epiphytes on the external wall of the mucilaginous tube, but without any selective distinction with regard to the polarity of the Berkeleya colony; they are arranged in small stellate colonies of three or more cells. Other tiny pennate cells of Nitzschia lecointei Van Heurck are frequently observed in the inner part of the mucilaginous tube where they seem to live free, and this latter species is suspected to live in symbiosis with B. adeliensis and perhaps may be commensal. The life habit of these three diatom taxa are described and illustrated in LM and SEM.