Morphological study of the marine planktonic diatom Chaetoceros castracanei Karsten from Antarctic waters, and possible taxonomic relationships

FERRARIO, M.E.; HERNÁNDEZ-BECERRIL, D.U.; GARIBOTTI, I.A.

Ottawa, Canadá

Simposio; 17th International Diatom Symposium; 2002

International Society for Diatom Research

During several phytoplankton surveys (including cruises of the Project Argau) along the north coast of the Antarctic Peninsula, the Weddell Sea and the Gerlache Strait, phytoplankton samples were collected using net (30 um mesh) and water pumps on different seasons in 1985, 1986, 1999, 2000 and 2001. Samples were fixed in formalin and lugol’s solution, respectively. Several diatom species of the genus Chaetoceros have been collected, identified and studied. A fairly common species is Chaetoceros castracanei Karsten, originally described in 1907, which morphology, distribution and taxonomy have not been investigated in detail. The species is present mainly in February and April, and was also recorded in subantarctic waters: it showed relatively high abundance in the Weddell Sea (up to 95238 cells l-1). Chaetoceros castracanei forms straight, medium-size to large chains, the terminal and intercalary setae are directed in the same direction (in girdle view), the apertures very reduced, centrally constricted and there are numerous chloroplasts in both cells and setae. Details studied by electron microscopy show valves randomly perforated by round poroids, no costae and a eccentric rimoportula in every valve of the chain: the setae are circular in cross section at the base, but become four-sided distally, there are perpendicular rows of elongate poroids, spines arranged in spirals along the setae and the tip is very pointed. The intercalary setae are fused together in sibling valves. We have found that the species Chaetoceros impressus Jensen et Moestrup, recently described for Danish waters, is coespecific with C. castracanei, and consequently we propose it as a synonym of the later. Therefore, the known distribution of Chaetoceros castracanei may woden to Antarctic, subantarctic and Danish waters. Other possible taxonomic relationships of the species are also discussed, especially regarding C. danicus.