A study was performed in the estuarine waters of the North-eastern Bay of Bengal on the influence of salinity in the governance of the frustular diameter of the centric diatom Coscinodiscus, in the Hooghly estuary, in India. The centric diatom Coscinodiscus was chosen to be the subject of the present study based on its ubiquitous habitat which includes varying salinity domains of the world wide estuaries in an attempt to truly understand the significance of the event on a global scale. The study encompassed tenure of two years, embracing three distinctly different salinity regions as sampling stations. The result reveals that an increase in salinity of the ambient medium always caused the reduction in the diameter of the cells and vice versa. The detailed correlation and regression values generated from tallying the nutrient concentration and fluctuation in frustular diameter revealed significantly negligible dependence of frustule diameters on that of the nutrients. This feature can be used as a potential ecological indicator in well mixed estuaries.