Distribution and ecology of <i>Pseudo-nitzschia</i> species (Bacillariophyceae) in surface waters of the Weddell Sea (Antarctica)

Abstract

The distribution of six <i>Pseudo-nitzschia</i> species and their relationship with environmental conditions were studied for the first time in a vast zone of the Weddell Sea (∼61–77°S, Antarctica). Both qualitative and quantitative phytoplankton samples, collected during summer 2004, were examined using light and scanning electron microscopy. Phytoplankton abundance and composition showed great variability along our study area. Diatoms were the most conspicuous phytoplankton group in the northern area while small flagellates were generally dominant in the southern stations. The genus <i>Pseudo-nitzschia</i> was broadly distributed and significantly contributed to total diatom densities. A marked contrast in <i>Pseudo-nitzschia</i> species distribution was observed in three main zones divided by the Weddell Front (WF) and the Antarctic Slope Front (ASF). <i>P. subcurvata</i> and <i>P. turgiduloides</i> were the most abundant species in the neritic Weddell Sea zone, south of the ASF, mainly near the ice-edge in shallower waters and in conditions of long photoperiod. In contrast, <i>P. prolongatoides</i> and <i>P. lineola</i> dominated north of the ASF; the first was associated with deeper and nutrient-rich waters whereas the latter showed a weak relation with environmental variables examined. Finally, <i>P. turgidula</i> and <i>P. heimii</i> were mostly observed in the Weddell–Scotia Confluence Zone in the warmest and far from ice covered waters, north of the WF. A brief morphological <i>Pseudo-nitzschia</i> species description is given in the Appendix, including morphometrics and pictures.