**7. Impact of HAB on animal and human health**

Frequent HAB events in a particular area are reported to endanger and kill marine organisms, especially fish, shellfish, birds, and other marine organisms on a large scale. HAB formation can be associated with either toxic or non-toxic phytoplanktons. Non-toxic species are responsible for discolouration sometimes for fish and shellfish mortality. In this case, oxygen depletion due to dense bloom is accountable for such killing. On the other hand, toxic species cause poisoning in marine fish and

bivalves, which renders large-scale fish killing and also severe health hazards for humans [54]. Ciguatera poisoning (CP) is the most common type of HAB-related contamination in fish. Dinoflagellates, *Gambierdiscus and Fukuyoa*, are attributed to produce ciguatoxins, which ultimately cause CP. Upon consuming contaminated fish, individuals may experience gastrointestinal, cardiovascular, and neurological disturbances [55].

Other HAB-related diseases include amnesic shellfish poisoning, caused mainly by *Pseudo-nitzschia* and *Nitzschia*; azaspiracid shellfish poisoning, caused by *Azadinium* and *Amphidoma*; diarrhetic shellfish poisoning, caused by Dinophysis, Phalacroma and Prorocentrum; neurotoxic shellfish poisoning, caused by *Karenia* and *Chatonella*; paralytic shellfish poisoning, caused by *Alexandrium, Gymnodinium* and *Pyrodinium*; and palytoxicosis ovatoxin poisoning, caused by Dinoflagellate, *Ostreopsis*. All of these poisonings are mainly associated with gastrointestinal, respiratory or neurological disturbances in humans. In severe cases, it may lead to coma or even death. HAB toxins kill marine piscine species and may amalgamate in these marine creatures, which may further transfer to the food web. This may affect other animals as well [56]. For example, birds, snakes and turtles found in HAB affected wetlands are reported to face sub-lithal effects. HAB toxins like microcystin can elevate physiological stress in these organisms, resulting in immune function or reproduction anomalies [57].

Besides direct consumption, exposure to HAB related toxins may also affect human health. Aerosolised brevetoxin from *Karenia brevis* is responsible for impaired respiratory function. This brevetoxin can spread quickly to the entire water column and maybe end up in the diet of the biota of that area. Not only that, this toxin has a detrimental impact on the larval stages of aquatic creatures [58].
