Harmful algal blooms (HABs), which are algal bloom events involving toxic or otherwise harmful phytoplankton such as dinoflagellates of the genus Alexandrium and Karenia, or diatoms of the genus Pseudo-nitzschia. Such blooms often take on a red or brown hue and are known colloquially as red tides.
Coastal HAB events have been estimated to have economic impacts in the United States of at least $82 million/year with the majority of impacts in the public health and commercial fisheries sectors (Hoagland and Scatasta 2006). This estimate is conservative due, in part, to a lack of information about individual events, unquantified economic effects of environmental impacts, and a lack of documentation of sociocultural impacts (such as loss of cultural practices and values, increased reliance on social services, decreased recreational opportunities, and shifts in livelihoods).
Nutrient loading from fossil fuel combustion, fertilizers and other sources in water bodies can lead to eutrophication. Eutrophication can create algal blooms or red tide, which can wreck havoc to marine organisms threatening seafood production, while simultaneously preventing human swimmers from safely enjoying the water during 95 degree July days.
The Gulf of Mexico Dead Zone’s hypoxic conditions have far reaching effects throughout the coastal and marine ecosystems. Organisms living in the hypoxic zone experience direct mortality, an altered food web, and habitat changes and loss. The loss of fisheries and oyster beds translates into an economic loss as commercial fishermen are forced to fish elsewhere or stop altogether, and recreational fishermen are no longer attracted to the area. The species that do remain in this area are further threatened by over- harvesting and are less appealing to consumers fearing disease. In addition, the same conditions, which produce the Dead Zone, also lead to other detrimental conditions such as Harmful Algal Blooms, which also cause many harmful effects.
Toxic plankton may be numerous enough to toxify shellfish... Although these algae pose not direct treat to humans, shellfish are particularly prone to contamination because the toxins they produce can be accumulated as mollusks feed by filtering microscopic food out of the water... Human and animal consumption of contaminated shellfish may generate severe poisoning effects because the Alexandrium fundyense, produces one of the most potent toxins known to scientists: saxitoxin.
Very recently, it has been argued that precipitation-driven coastal runoﬀ and associated anthropogenic nutrient loads may be responsible for Pseudo-nitzschia blooms oﬀ central California, and that upwelling might not be as important as is often suggested. Mass introduction of nutrients from North Carolina hog farm waste ponds resulted in an approximate 6-fold increase in Pﬁesteria piscicida zoospores, mimicking laboratory observations of zoospore responses to inorganic and organic enrichment.
The most severe, and therefore memorable, eﬀects of HABs include ﬁsh, bird, and mammal (including human) mortalities, respiratory or digestive tract problems, memory loss, seizures, lesions and skin irritation, as well as losses of coastal resources such as submerged aquatic vegetation and benthic epi- and in-fauna
Several phytoplankton species produce harmful blooms, known as red or brown tides, which release toxins in the water that can poison mollusks and fish. Excessively large blooms can also overwhelm a marine ecosystem by creating oxygen-depleted "dead zones" in the ocean. Scientists have long suspected that many harmful blooms are fueled by fertilizer runoff from farming operations, which in many regions pour tons of excess nitrogen and other nutrients into rivers that eventually flow into coastal waters.
Algal blooms occur naturally when cold-water upwellings bring from the seafloor to the surface nutrients that stimulate the rapid reproduction and growth of microscopic algae, also known as phytoplankton. These events often benefit marine ecosystems by generating tons of algae that are consumed by larger organisms.
1844 -- The first scientifically documented red-tide episode in U.S. waters occurs in the Gulf along what is called the West Florida Shelf, off the Panhandle near Panama City.
The occurrence of blue-green algae is natural and has occurred throughout history. Still, to better understand the phenomenon, Florida monitors blue-green algae closely because nutrient (such as nitrogen and phosphorus) pollution appears to intensify blue-green algae outbreaks... Algal blooms were documented in Florida’s coastal waters as early as the 19th century.