Ocean acidification means the lowering of pH values below 7.0 presumably caused by the atmospheric CO2 absorbance by seawater. Since coastal seawater allows to grow the respective ecosystem, which in turn allows them to absorb the atmospheric CO2 releasing O2 into the atmosphere, the excess CO2 absorbance by seawater may lead to the change in the seawater chemistry by altering natural seawater pH, alkaline in nature, into lowering the same toward acidic-- keeping the possibility of alteration of marine and coastal ecosystem pathways leading to uncertainties in such ecosystem’s productivity. The result of the experiment shows that the pH of the samples taken from different places of Visakhapatnam having two different ambiences (places/sampling spots from the open sea of Bay of Bengal and places/sampling spots from & nearby the Viskahapatnam natural port area) shows variations from each other. Open coastal seawater sample shows higher pH values as compared to that of harbour seawater. The rate of pH values determined in the subsequent year shows significant decrease in harbour seawater and having found a direct relationship with the dissolved oxygen content of the same. The result also shows that a very slight reduction of pH of the harbour seawater sample influenced in reducing the salinity, dissolved oxygen and total chlorophyll content. Keywords: Marine & Coastal Ecosystem, Bay of Bengal, pH, Ocean Acidification, Salinity, Dissolved Oxygen, Total Chlorophyll.