Karenia brevis produces brevetoxins that can be come airborne with the sea spray and cause fish kills, respiratory irritation and possibly other health effects in humans and other mammals occur. Some phytoplankton, such as Karenia brevis found in the Gulf of Mexico are severely harmful to humans and wildlife directly, either through water or air exposure. See the Red Tides article for details on various health threats by region. For instance, dinoflagellate algal blooms create "red tides" which can release strong neurotoxins, such as saxitoxin, that can be ingested by shellfish and passed on to humans who eat the infected shellfish. For red tides, people are exposed principally to the toxins produced by harmful phytoplankton through the consumption of contaminated seafood products. The human health threats and illnesses associated with harmful algal blooms are highly dependent on the location of the bloom, because that generally dictates what species of phytoplankton or algae is present. To learn more about red tides (lower left image) visit this article, and to learn more about cyanobacteria (lower right image) visit this article. Scientists now prefer the term, HAB, to refer to bloom phenomenon that contain toxins or that cause negative impacts. Certain species can even release a neurotoxin that becomes airborne, causing direct impacts to nearby humans and animals. Unfortunately, a small number of species also produce potent neurotoxins that can be transferred through the food web, where they affect and even kill the higher forms of life such as zooplankton, shellfish, fish, birds, marine mammals, and even humans that feed either directly or indirectly on them. These processes deplete the dissolved oxygen necessary for the survival of fish and other organisms. During these blooms, most of the phytoplankton eventually die and sink to the bottom, where they are decomposed by bacteria. The term "red tide" is thus a misnomer because they are not associated with tides. In saltwater, "Red tide" is a common name for such a phenomenon where certain phytoplankton species contain reddish pigments and "bloom" such that the water appears to be colored red. These blooms can threaten drinking water sources in freshwater environments, cause fish kills, and create anoxic, low-oxygen marine environments. Occasionally, the bacteria or phytoplankton grow very fast or "bloom" and accumulate into dense, visible patches near the surface of the water. The two most common types of harmful algal blooms are red tides, which are marine phytoplankton and cyanobacteria, also known as blue green algae, which mainly occur in freshwater but can migrate to marine environments. They absorb nutrients and carbon dioxide from the water and produce oxygen through photosynthesis. Phytoplankton are believed to generate as much as 80% of the world's oxygen supply. Most species of algae or phytoplankton (plant plankton) are not harmful and serve as the energy producers at the base of the food web, without which higher life on this planet would not exist. Harmful algae are microscopic, single-celled plant-like organisms that live in the sea. This website has numerous useful links to scientific information, human health impacts, and impacts to animals from harmful algal blooms. Much of the following information was taken from the website "Harmful Algae: Red Tide" from Woods Hole Oceanographic Institution.
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