Coscinodiscus Ehr. species: morphology and distribution

FERRARIO, M. E.; LICEA, S.; ALMANDOZ G. O.; GARIBOTTI, I.

Miedzyzdroje, Polonia

Simposio; 18th International Diatom Symposium 2004; 2004

International Society for diatom research & University of Szczecin, Poland

The genus Coscinodiscus is an important component of the marine phytoplankton and several core sediments intervals (Sancetta, 1987), and has been registered in the fossil record since the Late Cretaceous (Strelnikova et al. 1998). Coscinodiscus species are well represented in modern Argentinean ocean samples, although most of these studies are based on light microscopy (LM). We analyzed plankton material from different areas in Antarctica, Argentina and Mexico in order to provide a narrow definition of the living Coscinodiscus species and investigate the inter-population morphological variability using both LM and Scanning Electron Microscopy. The study area include Argentinean continental shelf, Drake Passage, Antarctic Peninsula and the Gulf of Mexico. Qualitative (30 µm net pore) and quantitative samples were taken at 9 m depth, fixed with lugol and prepared and mounted using standard procedures. The analyzed samples were compared to mounted slides from the Frenguelli collection, Series Ns 167 (1-2-3-4), from Argentinean ocean samples. We followed the diatom terminology suggested by Von Stosch (1980), Hasle & Lange (1992), Fryxell & Ashwoth (1988). We identified the following species: C. granii Gough, C. radiatus Ehrenberg, C. oculoides Karsten, C. asteromphalus Ehrenberg, C. marginatus Ehrenberg, C. gigas Ehrenberg, C. jonesianus (Ehrenberg) Ostenfeld, C. alboranii Pavillard, C. bouvet Karsten and C. janischii Schmidt. The genus Coscinodiscus has locular areolae and labiatae processes without external tubuli as diagnostic features. These two morphological characters are present in all the analyzed species except C. janischii, C. alboranii and C. jonesianus. C. janischii has both locular and poroid areolae (Ferrario & Sar, 1990), whereas C. alboranii presents typical locular and poroid areolae and another type of areolae “endochiastic areolae” with a complex structure not described yet for another species (Von Stosch, 1985). C. jonesianus has macro-labiate processes with external tubuli and complex morphology. Most of the discussed Coscinodiscus species have a wide geographical distribution, although we observed that C. bouvet is an endemic species from Antarctica, C. alboranii occurs in Australia and Gulf of Mexico, and C. janischii, a rarely cited species in the bibliography, is common in several Argentinean coastal localities. The inner-population morphological variability was minimal.