Phytoplankton distribution pattern and its implication for the establishment of land-based ballast water treatment technology and test facility in tropical waters

The present study was carried out to investigate the phytoplankton distribution in tropical waters and its implication for establishing land-based ballast water treatment technology and test facility (BWTT-TF) as per the International Maritime Organization (IMO) guidelines. Samples were collected from the Swarnamukhi estuary (SE) and coastal locations on the east and west coast of India. The maximum phytoplankton density in the size group of ≥10 and < 50 μm was recorded as 3002 cells/mL in estuarine waters and 172 cells/mL in coastal waters. Among the phytoplankton, Bacillariophyta and Pyrrophyta were observed at all locations, whereas Ochrophyta and Chlorophyta were found only at specific locations or during specific periods. According to IMO guidelines, the minimum required number of species (5) was observed at all the locations, but the minimum number of phyla (3) was not found at some locations. The IMO minimum required phytoplankton density (>1000 cells/mL) was observed only during the bloom period, whereas it was about 5–50 times lower during other periods. Taxonomic distinctness indices were used to examine the diversity beyond the conventional species count. The study found that the Buckingham Canal and Swarnamuki River upstream among the SE locations, and coastal stations of Pamanji and Tirunelveli among the coastal locations, are suitable sites to establish land-based BWTT-TF. Since the results indicate that achieving the IMO specified size group of ≥10 and < 50 μm density in tropical waters was possible only during the bloom period, culturing phytoplankton surrogates and concentrating naturally available phytoplankton are recommended as alternate methods for establishing land-based ballast water treatment technology and test facilities.