Distribution of extant coccolithophores from the northwest continental shelf of India during the summer monsoon

Abstract

Coccolithophores contribute substantially to marine primary production as well as to particulate inorganic carbon (PIC) flux to the deep sea; however, there is no literature available so far from the Indian continental shelf on this functional group. We present here the first study describing the spatial variability and species composition of living coccolithophore communities from the north-western continental shelf waters (northeastern Arabian Sea) of India (SW monsoon; August 2018). We found a total of 18 species from 11 genera with Gephyrocapsa oceanica as the dominant coccolithophore. Florisphaera profunda, Calcidiscus leptoporus, Helicosphaera carteri and Umbilicosphaera sibogae were also observed in significant quantities in most of the stations. Cell abundances ranged from 0.3 to 85.6 � 103 l-1 with the maximum occurrence at the northernmost station. Coccolithophore diversity was comparatively higher in the southernmost region, while high dominance was noticed in the north. Redundancy analysis (RDA) revealed that nutrient availability was an important factor to modulate the distribution and abundance of coccolithophores. Gephyrocapsa oceanica was recorded in each station and showed a positive association with NO2- + NO3- levels, whereas F. profunda and U. sibogae were confined mostly to deepwater. Our study shows that a substantial number of coccolithophores are present in the shelf water and could be important as primary producers as well as for the carbon export flux. Further research attention to broaden our knowledge of the role of this functional group is warranted.