Marine Cocconeis Ehrenberg (Bacillariophyceae) species and related taxa from Kerguelen's Land (Austral Ocean, Indian Sector)

Recent marine species of Cocconeis Ehrenberg, and related taxa (Bacillariophyceae) from sub-Antarctic Kerguelen Islands sediments (Indian sector of the Austral Ocean) were analyzed. Predominant and fast?growing macroalgae cover [kelp, mainly Macrocystis pyrifera (Linné) and Durvillaea antarctica (Chamisso in Choris)] favored epiphytism, and give an opportunity for attached genera to proliferate and develop a large diversity. Based on material collected during four austral summers between 1985 and 1992, almost 40 Cocconeis and some related taxa were described. Several of them are new for these Austral localities (cf. Taxa Index), while others remain taxonomic uncertainties. The diversity was particularly high under the M. pyrifera canopy. Some species were found as epiphytes on larger diatoms, while other very tiny taxa were predominantly epipsammic. Some taxa exhibited a wide range of dimensions as well as variability in their ornamentation. Communities were different at each locality, in relation with tidal variation, macroalgal canopy, or presence of mussel beds. Some of Cocconeis species are ubiquitous, whereas others seem so far to be endemic or restricted to these Austral islands. Cocconeis scutellum Ehrenberg and its varieties are dominant in a large range of subtidal sediments. C. fasciolata (Ehrenberg) Brown or C. stauroneiformis (W. Smith) Okuno are also important components. Some taxa were wrongly identified or poorly illustrated by earlier authors, so that this study clarifies several taxonomic uncertainties. The scanning electron microscopy (SEM) was used to illustrate each taxon. Descriptions based on SEM, and light microscopy, when possible, are presented. Specificities of the Austral diatom flora and particularly those of Kerguelen?s Land are emphasized.