Water quality characteristics and phytoplankton of polluted Visakhapatnam Harbour

Data on water quality characteristics and phytoplankton communities of the polluted Visakhapatnam Harbour were collected for 3 years from April 1980 to March 1983. The waters of the harbour were highly turbid, and the BOD and dissolved oxygen content varied in the six stations selected. The concentrations of nutrients and heavy metals found in the harbour was 2–300 times higher than that of coastal waters. Fifty species of phytoplankton, belonging to Cyanophyceae, Chlorophyceae, Euglenophyceae, Bacillariophyceae and Dinophyceae were found in different stations. Standing crops of nanoplankton (2–20 μm), blue-green algae, Ankistrodesmus falcatus, Nitzschia longissima and Thalassiosira decipiens, were at a maximum at the severely polluted station I; dinoflagellates, Skeletonema costatum and Cyclotella menegheniana, were highest at the moderately polluted Stations III and IV and many diatoms dominated the less polluted Stations V and VI. The composition and species diversity varied between plankton of harbour stations and open waters. S. costatum was the dominant species among the microplankters of the harbours. Mean standing crop of total plankton varied from 18·0 to 54·0 × 10 5 cells litre −1 in surface waters of Station I to VI and the contribution of nanoplankton was 73·4 to 91·8% of total densities of algal crop. Both nano- and micro-plankton decreased from surface to 4 or 6 m. Nanoplankton was not observed at 6 m. Cell densities varied in the six harbour stations in relation to changes in the nutrient concentrations, BOD and turbidity of the water. Minimum circulation, accumulation and utilization of nutrients appear to be responsible for the excessive growth of primary producers and oxygen supersaturation observed in the waters of Visakhapatnam Harbour.