Morphological variability of Emiliania huxleyi in the Indian sector of the Southern Ocean during the austral summer of 2010

• E. huxleyi morphotypes A, B, C, B/C, var. corona and type D recorded in the study region.
• E. huxleyi morphotypes A, B and var. corona dominate north of the SSTF.
• E. huxleyi morphotypes B/C and C dominate in the SSTF, SAF and PF regions.
• E. huxleyi was recorded as far as 65°S latitude.
• E. huxleyi morphotypes C and B/C are better adapted to the SSTF, SAF and PF regions.

We documented scanning electron micrographs of Emiliania huxleyi morphotypes from 9 vertical profile samples collected between 39°S and 65.49°S (57.3°E) during the Fourth Indian Southern Ocean expedition (January–February, 2010). Water samples were obtained from 6 different depths (between 0 and 110 m) to study the distribution and abundance of E. huxleyi morphotypes with respect to associated environmental factors in the oceanic frontal regions of the Southern Indian Ocean. Five E. huxleyi morphotypes were identified, quantified and the preference of each morphotype with regard to physico-chemical parameters assessed by Canonical Correspondence Analysis (CCA). Morphotypes A and B comprised 6.2% and 0.7% of the total E. huxleyi abundance, respectively, and dominated at stations located north of the Southern Subtropical Front (SSTF) associated with warmer, highly saline and nutrient-poor surface waters. Morphotypes C and B/C are cold water forms representing 23.2% and 68.5% of the total E. huxleyi abundance, respectively, and dominated in the Subantarctic (SAF2) and Polar Frontal (PF1) regions of the Southern Indian Ocean. Morphotypes C and B/C dominated in the SAF2 and PF1 regions, which were identified as the most productive areas due to the elevated nutrient concentrations. Salinity, nitrate, phosphate and probably light intensity were the most important parameters for the proliferation of E. huxleyi in these frontal regions. Towards the south, a consistent decrease in the E. huxleyi abundance was observed and their lowest abundance recorded at the southernmost station located in the Antarctic coastal region (65.49°S).