61 A three-year record of red tides in Chabahar coastal waters (North of Gulf of Oman) Emad Koochaknejad 1 *, Amir Ghazilou 1 , Hamid Ershadifar 1 , Kamalodin Kor 1 , Abdolvahab Maghsoudlou 1 1- Department of Marine Biologyy, Faculty of Marine Science, Iranian National Institute for Oceanography and Atmospheric Sciences (INIOAS) Received: May 2016 Accepted: September 2016 © 2016 Journal of the Persian Gulf. All rights reserved. Abstract Seven phytoplankton species (Alexandrium sp., Prorocentrum micans, Cochlodinium (aka Margalefidinium) polykrikoides, Mesodinium rubrum, Akashiwo sanguinea, Gonyaulax polygramma, Ceratium sp.) were found as the main cause of Harmful algal blooms (HABs) in a three-year record of red tides in Chabahar coastal waters (North of Gulf of Oman). Autumnal blooms of Gonyaulax polygramma and Prorocentrum micans are reported for the first time in the region. The most frequent bloom events were caused by Akashiwo sanguinea (i.e. 4 times) and Mesodinium rubrum (i.e. 3 times). The highest observed density was at Oct 2017 caused by Akashiwo sanguinea (15.3*10 6 / litre). The recorded temperature range was from 24.4 to 31.5°C and the DO ranged widely from 3.9 to 11.2 mg/liter. In conclusion, HABs occurrences are not associated with the expansion of one particular species but with multiple taxa and there is a suitable environmental condition for HABs in the autumn and spring in the region. Keywords: HABs, Red tide, Chabahar, Gulf of Oman, Akashiwo sanguinea 1. Introduction Harmful algal blooms (HABs) are increasing phenomenon in the coastal waters of the world in terms of frequency and intensity (Glibert et al., 2015), causing unfavorable effects on marine ecosystems (Anderson et al., 2015). In the Gulf of Oman, HABs and their impacts have become more widespread and persistent (Al-Azri et al., 2007, Thangaraja et al., 2007). The coastal waters of Chabahar within the northern part of the Gulf are no exception to this pattern. Annual winter bloom of the green Noctiluca scintillans constitutes the major HABs of the area. The species has expanded across the Indian Ocean, the Arabian Sea, and the Gulf of Oman over the past few decades (Harrison et al., 2011). Yet, N. scintillans is not the only case of HABs and blooms of several other dinoflagellates and ciliates are common in this area. In one occasion a large-scale bloom of Prorocentrum micans, not only led to shot down of a desalination plant and cut off of the city's tap water for a week, but also imposed damages to one shrimp breeding site in 2017. These events have caused significant concerns Journal of the Persian Gulf (Marine Science)/Vol. 7/No. 25/ September 2016/6/61-66 * Email: emad.koochaknejad@inio.ac.ir Downloaded from jpg.inio.ac.ir at 6:06 IRST on Thursday November 25th 2021