M.A. Asefi - Department of Marine Biology, Faculty of Marine Sciences, Chabahar Maritime University, Chabahar, Iran
G. Attaran Fariman - Department of Marine Biology, Faculty of Marine Sciences, Chabahar Maritime University, Chabahar, Iran
G. Mohammadpour - Iranian National Institute for Oceanography and Atmospheric Science, Faculty of Atmospheric Sciences, Tehran, Iran

The present study reports widespread aquatic mortality during an unprecedented harmful algal blooms (HABs) in Chabahar Bay, the largest bay of the Oman Sea and one of the most important fishing areas of Iran, on ۱۵ and ۱۶ June ۲۰۱۹. This volume of aquatic death stopped fishing and tourist activities in this area for a short time. During this event, the microalgae Karlodinium Cf. veneficum with a density of ۶.۸ × ۱۰۴ cells mL−۱ was identified as the bloom former species. The toxic dinoflagellate K. veneficum has contributed to the aquatic mortality in many coastal areas of the world by producing karlotoxin. The phytoplankton community was studied in this bloom and ۴۶ species of phytoplankton were identified, including ۲۲ species of diatoms,  dinoflagellates (۲۲),  Cryptophyta (۱), and  Chlorophyta (۱). This is the first occurrence of HABs associated with the dinoflagellate Karlodinium bloom and the first report of the presence of two toxic and dinoflagellate species, Amphidinium carterae and Ostreopsis ovata associated with the algal bloom in the northern  Oman Sea. Chabahar Bay is considered one of the most important areas of aquatic fishing grounds in the region.  The occurrence of HABs regarding toxic dinoflagellates can be a serious risk to aquaculture activities, human health, and the ecosystem in the area. Water consumption of the residents of Chabahar relies on desalination plants, therefore the bloom of toxic microalgae in the Chabahar bay can disrupt the operation of the desalination plant and pose a potential threat to the water supply in this area.

Dinoflagellate, Aquatic mortality, Red tide, Chabahar Bay, HABs