Environmental triggers and ecological implications of a harmful algal bloom in the northern Arabian/Persian Gulf: Insights into the driving forces and consequences

The Arabian/Persian Gulf, a marginal sea of the northern Indian Ocean, has been significantly impacted by human activities, leading to a rise in harmful algal blooms (HABs). This study investigates the summer blooming of an ichthyotoxic phytoflagellate Chattonella marina var. antiqua and associated fish-kill in Kuwaiti waters, connecting the events to a previous dust storm and eutrophication status in the coastal waters of the Northern Arabian Gulf (NAG). Pre- and post-fish-kill sampling revealed significant differences in Chattonella cell densities and environmental conditions, with cell densities reaching 435 × 10³ cells L⁻¹ in the post-fish-kill period. Chattonella structural properties and environmental conditions reported significant differences between the fish-kill and non-fish-kill areas. Apparent Oxygen Utilization patterns suggested higher organic carbon remineralization in areas with dense Chattonella density, suggesting the bloom's potential to promote heterotrophic activities in the water column. The toxicity levels and structural properties of Chattonella positively correlated with deteriorating water quality. We postulate that a severe dust storm that occurred two months before the bloom played a critical role in enhancing the nutrient availability, which, supplemented with an allochthonous nutrient supply and a genetically programmed, temperature-dependent excystment of Chattonella cysts, initiated the vegetative cell growth of Chattonella culminating in a bloom. It is postulated that the increased water temperatures, reduced dissolved oxygen solubility, elevated metabolic rates in fish, and the ichthyotoxins secreted by the bloom impaired fish respiratory mechanisms and caused fish mortality. Thus, this study explains the possible long-term effects of summer dust storms in the northern Arabian Gulf, as understanding the role of environmental mechanisms triggering HABs is vital to comprehend their ecological implications in coastal marine systems.