ICE DIATOM, SYNEDROPSIS LATA VAR. LATA HASLE, MEDDLIN & SYVERSTSEN, FROM NORTHWEST WEDDELL SEA, ANTARCTICA. MORPHOLOGY, HABIT AND DISTRIBUTION.

MARTHA FERRARIO; ADRIÁN CEFARELLI; MARIA VERNET

Minnesota

Simposio; 21st International Diatom Symposium; 2010

The araphid diatom genus Synedropsis, was stablished by Hasle, Meddlin & Syverstsen (1994). The generitype, Synedropsis hiperborea (Grunow) Hasle, Meddlin & Syverstsen, was first considered as a species of Synedra. The main morphological structure is an apical field, composed of slits separated by 3 o more bars. The species of genus are better represented in the Antarctic than in the Arctic usually associated to sea ice habitats or in warm waters and. Around ten Synedropsis species have been reported, among these, Synedropsis cheethamii was found in upper Oligocene sediments, marking the earliest fossil register of this genus. Recently were added the first warm waters registers, Synedropsis roundii from southeastern Brasil and Synedropsis Karsteteri, from northeastern gulf of Mexico. Both species were found forming extensive bloms. During the expeditions Iceberg I and III (December 2005; March to April 2009) in the framework of the project ?Free-drifting Icebergs as Proliferating Dispersion Sites of Iron Enrichment, Organic Carbon Production and Export in the Southern Ocean?, a Phantom DS-2 remote operating vehicle (ROV) was used to sample from the submerged iceberg flanks, in North West Weddell Sea, Antarctica. The Cualitative samples were preserved with 2% acid Lugol?s iodine solution, treated and mounted for light (LM) and scanning electron microscope (SEM) using standard procedures. In this study we describe Synedropsis lata var. lata, an epiphytic species of Thalassioneis signyensis, a dominant epilithic species attached to sand-grained-sized rocks included in the ice which was found forming small tufts in the iceberg flanks. Its main morphological characters were valves narrowly elliptical, with dilated central part, sternum occupying the entire valve face and apical slit fiels with different number of slits in each pole. Synedropsis lata var. lata, was distinguished from each other species of the genus, mainly by the valve striation density, the structure of apical field and position of the labiated process/rimportula. Comparisons and discussion with allied genera such as Brandinia, Fossula, Fragilaria, Ulnaria and Thalassioneis are made. Also environmental data are given and are compared with the previous studies.