Phytoplankton from the Southwestern Atlantic Ocean: morphology, taxonomy and distribution of selected small-size diatoms

FERRARIO, M. E.; SALA, S.; ALMANDOZ G. O.; CEFARELLI, A.

Irkutsk, Rusia

Simposio; 19th International Diatom Symposium 2006; 2006

International Society for Diatom Research & the Limnological Institute of the Siberian Branch of the Russian Academy of Science

The Southwestern Atlantic Ocean is recognized as one of the most productive areas in the world and supports a very rich fishery. However, paradoxically the phytoplankton taxocenosis is poorly known. Addressed to study the biodiversity and seasonal phytoplankton dynamic in Argentinean continental shelf and slope waters (38-55°S), a cooperative research program (GEF- Patagonia, Argentina) has been recently established. In the frame of this Project, we present a preliminary report based on the first oceanographic cruise performed during spring 2005. The main goal of the present study was to provide information related to selected small-size diatoms, which are easily misidentified when examined with light microscopy and therefore, have not been reported or sporadically mentioned in previous surveys. A total of 81 oceanographic stations were performed. Samples for qualitative (30 µm net mesh) and quantitative analyses were collected at 9 m depth using a continuous seawater pumping system. The qualitative material, preserved with Lugol solution, was treated and mounted for light (LM) and scanning electron microscopes (SEM) using standard procedures. On the basis of the analysis of the ultrastructure, taxonomy and distribution, 11 species are discussed, 5 of them are reported for the first time in the SW Atlantic Ocean. Minidiscus trioculatus (Taylor) Hasle and M. decoratus Chrétiennot-Dinet & Quiroga, are reported for the first time in the SW Atlantic, and compared with M. chilensis Rivera & Koch, the only species previously reported for this region. The analyses of morphological variation of several specimens of Cyclotella littoralis Lange & Syvertsen, originally described for this area, show a great similarity with Cyclotella baltica (Grunow) Håkansson. Consequently, we discuss their possible taxonomic relationships. The presence of Triblioptychus cocconeiformis (Hendey) A. Prasad,  Thalassiosira proschkinae var. spinulata (Takano) Makarova and Thalassiosira oceanica Hasle is registered for the first time. In the present survey the two former were common components in coastal waters while the later was frequently collected in oceanic waters. In this area, Pseudopodosira westii (Smith) Sheshukova & Gleser, Plagiogrammopsis vanheurkii (Grunow) Hasle, von Stosch & Syvertsen, Cymatosira belgica Grunow and Campylosira cymbelliformis (A. Schmidt) Grunow were only previously studied (LM) by Frenguelli. Their identity is confirmed based on SEM analysis and also their distribution is expanded. Part of this information was previously communicated in Latin American meetings.