Diatom assemblages at subsurface chlorophyll maximum layer in the eastern Indian sector of the Southern Ocean in summer

Abstract

We examined and compared species composition of the diatom assemblages in the surface mixed layer and subsurface chlorophyll maximum (SCM) layer in the eastern Indian Sector of the Southern Ocean during the summers of 2002 and 2003. In both years, the SCM formed below the mixed layer and within the temperature minimum layer. Among all diatom taxa (56 species and 10 generic groups) identified, 13 were classified as dominant taxa and they had wide variable cell sizes. This makes the SCM a widely available foraging site for a variety of grazers of different sizes. Bray–Curtis similarity index indicated that species composition of the assemblages was similar in the mixed layer and in the SCM at most stations. Cluster analysis revealed that three assemblages in the SCM detected in 2003 were clearly different from those from a single SCM assemblage in 2002. Comparisons among data from this and previous studies suggest that there are no unique SCM assemblages in the area, and that assemblages in the SCM have high regional and interannual variability in species composition, which would cause their availability for various grazers to be variable.