Investigation on ballast water exchangeable area in the Bay of Bengal using MODIS/Aqua

The ballast water exchange at seas has been recognized as one of the operational countermeasures to cope with the invasion of non-indigenous species through the ballast water. The Bay of Bengal is traditionally considered to have low chlorophyll-a concentration thus low phytoplankton counts, which is the reason why the Bay of Bengal (BoB) has been selected as a suitable ballast water exchangeable sea. However an anomalously high K(490) area was found off the coast of Sri Lanka during the northeast monsoon in 2005, which corresponds to higher plankton cell densities than the criterion set by the regulation of International Maritime Organization (IMO). The regression equation between K(490) and corresponding in situ plankton cell densities in the Bay of Bengal is developed to identify suitable ballast water exchangeable area based on the regulations of IMO. According to the results the central and eastern portions in the Bay of Bengal during the northeast monsoon season are found to be suitable, while the unsuitable area broadens during the southwest monsoon season at the western Bay of Bengal. Seasonal and annual variability of K(490) and corresponding cell density is discussed to establish an early routing system for avoiding the high cell density area in advance.