KARACHI: On early Wednesday morning, residents of Karachi in different parts of the city smelled a weird foul odor, but despite passage of more than two days, Pakistan Meteorological Department (PMD) or any other official department could not find the mystery behind the strange smell.The strong smell was reported in different parts of the city particularly felt in South, East and Central districts along the coastal belt. “It smelt like rotten eggs or decomposed fish,” said a woman, resident of an apartment building in Saddar town.No plausible reason was attributed to the cause of the stench. However, officials of World Wildlife Fund for Nature, WWF-Pakistan think that it was caused by decay of small planktonic dinoflagellate called Noctiluca scintillans. Mass bloom of this small free floating organism was reported from the Arabian Sea including the Pakistan coast. It is reported that the bloom was more prominent along the Pakistan and Oman coasts. According to WWF-Pakistan, the green bloom along Pakistan’s coast started appearing in February 2017 and continued till late May with a peak in March and April. In some areas the sea water even turned into green soup.Noctiluca scintillans blooms have been reported from Pakistan’s coast on many occasions. They occur in two forms, i.e. orange (or red) and green, which sometimes result in the mortality of fish and shellfish. During the current year the mass scale green bloom occurred but no mortality of fish or shellfish has been reported from Pakistan so far. However, mass scale mortality of pelagic shrimp and associated fishes was reported from Oman coast. Fishermen reported discolouration of water during the last five months. A reversal of current and wind patterns under the influence of the southwest monsoon in late May has resulted in the decay of the bloom, which caused the atypical stench in coastal areas of Karachi.“The blooms of Noctiluca scintillans (commonly known as sea sparkle) occur at least twice a year,” said Muhammad Moazzam Khan, Technical Advisor (Marine Fisheries), WWF-Pakistan. However, he said, in some years, the intensity of such bloom increases substantially and results in fish mortality in some cases. He also said that the onset of the monsoon results in a change in current pattern and due to this Noctiluca starts dying and results in an atypical odor. ‘The smell is not generally harmful,’ he added.While, Rab Nawaz, Senior Director Programmes, WWF-Pakistan pointed out that the frequency of such blooms is increasing in Pakistan which may be attributed to climate change. However, other anthropogenic factors may be the cause of such blooms.