Harmful algal bloom

[2][3] Effects of HABs can worsen locally due to wind driven Langmuir circulation and their biological effects.HABs from cyanobacteria (blue-green algae) can appear as a foam, scum, or mat on or just below the surface of water and can take on various colors depending on their pigments.

In a broader definition, all "organisms and events are considered to be HABs if they negatively impact human health or socioeconomic interests or are detrimental to aquatic systems".

Coastal HABs are a natural phenomenon,[31][32] although in many instances, particularly when they form close to coastlines or in estuaries, it has been shown that they are exacerbated by human-induced eutrophication and / or climate change.

Domoic acid readily accumulates in the bodies of shellfish, sardines, and anchovies, which if then eaten by sea lions, otters, cetaceans, birds or people, can affect the nervous system causing serious injury or death.

[41] Blooms of harmful algae can have large and varied impacts on marine ecosystems, depending on the species involved, the environment where they are found, and the mechanism by which they exert negative effects.

[43] The growth of marine phytoplankton (both non-toxic and toxic) is generally limited by the availability of nitrates and phosphates, which can be abundant in coastal upwelling zones as well as in agricultural run-off.

[52] Residual nutrients in treated wastewater can also accumulate in downstream source water areas[53] and fuel eutrophication, which leads progressively to a cyanobacteria-dominated system characterized by seasonal HABs.

[68] Although HABs in the Gulf of Mexico were witnessed in the early 1500s by explorer Cabeza de Vaca,[69] it is unclear what initiates these blooms and how large a role nanthropogenic and natural factors play in their development.

In 2015 the Ohio River had a bloom which stretched an "unprecedented" 650 miles (1,050 km) into adjoining states and tested positive for toxins, which created drinking water and recreation problems.

[105] Alan Steinman of Grand Valley State University has explained that among the major causes for the algal blooms in general, and Lake Erie specifically, is because blue-green algae thrive with high nutrients, along with warm and calm water.

[107] Toxic algae blooms are thought to play a role in humans developing degenerative neurological disorders such as amyotrophic lateral sclerosis and Parkinson's disease.

[21] Humans are affected by the HAB species by ingesting improperly harvested shellfish, breathing in aerosolized brevetoxins (i.e. PbTx or Ptychodiscus toxins) and in some cases skin contact.

[95] Because data collection has been more difficult and limited from sources outside the U.S., most of the estimates as of 2016 have been primarily for the U.S.[121] In port cities in the Shandong Province of eastern China, residents are no longer surprised when massive algal blooms arrive each year and inundate beaches.

[125] One of the few dead zones to ever recover was in the Black Sea, which returned to normal fairly quickly after the collapse of the Soviet Union in the 1990s due to a resulting reduction in fertilizer use.

[137] Environmental expert Lester Brown has written that the farming of salmon and shrimp in offshore ponds concentrates waste, which contributes to eutrophication and the creation of dead zones.

For example, a mass mortality event of 107 bottlenose dolphins occurred along the Florida panhandle in the spring of 2004 due to ingestion of contaminated menhaden with high levels of brevetoxin.

[181][182] Research is ongoing to determine the efficacy of floating mats of cattails in removing nutrients from surface waters too deep to sustain the growth of wetland plants.

For large algal blooms, however, adding algaecides such as silver nitrate or copper sulfate can have worse effects, such as killing fish outright and harming other wildlife.

[190] Cyanobacteria can also develop resistance to copper-containing algaecides, requiring a larger quantity of the chemical to be effective for HAB management, but introducing a greater risk to other species in the region.

[73] Some countries surrounding the Baltic Sea, which has the world's largest dead zone, have considered using massive geoengineering options, such as forcing air into bottom layers to aerate them.

In 2008 similar sensors in the Gulf forewarned of an increased level of toxins that led to a shutdown of shellfish harvesting in Texas along with a recall of mussels, clams, and oysters, possibly saving many lives.

[206][207][208][209] Four U.S. federal agencies—EPA, the National Aeronautics and Space Administration (NASA), NOAA, and the U.S. Geological Survey (USGS)—are working on ways to detect and measure cyanobacteria blooms using satellite data.

[211] In 2016 automated early-warning monitoring systems were successfully tested, and for the first time proven to identify the rapid growth of algae and the subsequent depletion of oxygen in the water.

[258] Several Caribbean countries considered declaring a state of emergency due to the impact on tourism as a result of environmental damage and potentially toxic and harmful health effects.

The Gulf of Maine frequently experiences blooms of the dinoflagellate Alexandrium fundyense, an organism that produces saxitoxin, the neurotoxin responsible for paralytic shellfish poisoning.

The well-known "Florida red tide" that occurs in the Gulf of Mexico is a HAB caused by Karenia brevis, another dinoflagellate which produces brevetoxin, the neurotoxin responsible for neurotoxic shellfish poisoning.

California coastal waters also experience seasonal blooms of Pseudo-nitzschia, a diatom known to produce domoic acid, the neurotoxin responsible for amnesic shellfish poisoning.

[269] Recent algae blooms in Lake Erie have been fed primarily by agricultural runoff and have led to warnings for some people in Canada and Ohio not to drink their water.

Cleanup crews hired by authorities in Lee County - where the Caloosahatchee meets the Gulf of Mexico - removed more than 1700 tons of dead marine life in August 2018.

[281] In 2020, a large harmful algal bloom closed beaches in Poland and Finland, brought on by a combination of fertilizer runoff and extreme heat, posing a risk to flounder and mussel beds.