HOME

TheInfoList



OR:

A harmful algal bloom (HAB) (or excessive algae growth) is an
algal bloom An algal bloom or algae bloom is a rapid increase or accumulation in the population of algae in freshwater or marine water systems. It is often recognized by the discoloration in the water from the algae's pigments. The term ''algae'' encompass ...
that causes negative impacts to other organisms by production of natural algae-produced toxins, mechanical damage to other organisms, or by other means. HABs are sometimes defined as only those algal blooms that produce toxins, and sometimes as any algal bloom that can result in severely lower oxygen levels in natural waters, killing organisms in
marine Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military ...
or
fresh water Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does incl ...
s. Blooms can last from a few days to many months. After the bloom dies, the microbes that decompose the dead algae use up more of the oxygen, generating a " dead zone" which can cause fish die-offs. When these zones cover a large area for an extended period of time, neither fish nor plants are able to survive. Harmful algal blooms in marine environments are often called "red tides". It is sometimes unclear what causes specific HABs as their occurrence in some locations appears to be entirely natural, while in others they appear to be a result of human activities. In certain locations there are links to particular drivers like nutrients, but HABs have also been occurring since before humans started to affect the environment. HABs are induced by
eutrophication Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phyt ...
, which is an overabundance of nutrients in the water. The two most common nutrients are fixed nitrogen (
nitrate Nitrate is a polyatomic ion with the chemical formula . Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are soluble in water. An example of an insolu ...
s,
ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous ...
, and
urea Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid. Urea serves an important ...
) and
phosphate In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid . The phosphate or orthophosphate ion is derived from phosph ...
. The excess nutrients are emitted by
agriculture Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled people ...
, industrial pollution, excessive
fertilizer A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
use in urban/suburban areas, and associated
urban runoff Urban runoff is surface runoff of rainwater, landscape irrigation, and car washing created by urbanization. Impervious surfaces (roads, parking lots and sidewalks) are constructed during land development. During rain , storms and other precip ...
. Higher water temperature and low circulation also contribute. HABs can cause significant harm to animals, the environment and economies. They have been increasing in size and frequency worldwide, a fact that many experts attribute to global
climate change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...
. The U.S.
National Oceanic and Atmospheric Administration The National Oceanic and Atmospheric Administration (abbreviated as NOAA ) is an United States scientific and regulatory agency within the United States Department of Commerce that forecasts weather, monitors oceanic and atmospheric conditi ...
(NOAA) predicts more harmful blooms in the
Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the conti ...
. Potential remedies include chemical treatment, additional reservoirs, sensors and monitoring devices, reducing nutrient runoff, research and management as well as monitoring and reporting. Terrestrial runoff, containing fertilizer, sewage and livestock wastes, transports abundant nutrients to the seawater and stimulates bloom events. Natural causes, such as river floods or
upwelling Upwelling is an physical oceanography, oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water from deep water towards the ocean surface. It replaces the warmer and usually nutrient-depleted ...
of nutrients from the
sea floor The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean. All floors of the ocean are known as 'seabeds'. The structure of the seabed of the global ocean is governed by plate tectonics. Most of ...
, often following massive storms, provide nutrients and trigger bloom events as well. Increasing coastal developments and aquaculture also contribute to the occurrence of coastal HABs. Effects of HABs can worsen locally due to wind driven
Langmuir circulation In physical oceanography, Langmuir circulation consists of a series of shallow, slow, counter-rotating vortices at the ocean's surface aligned with the wind. These circulations are developed when wind blows steadily over the sea surface. Ir ...
and their biological effects.


Description and identification

HABs from
cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, bl ...
(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. Cyanobacteria blooms in freshwater lakes or rivers may appear bright green, often with surface streaks which looks like floating paint. Cyanobacterial blooms are a global problem. Most blooms occur in warm waters with excessive nutrients. The harmful effects from such blooms is due to the toxins they produce or from using up oxygen in the water which can lead to fish die-offs."What you need to know about toxic algae blooms"
''USA Today'', August 7, 2015
Not all
algal bloom An algal bloom or algae bloom is a rapid increase or accumulation in the population of algae in freshwater or marine water systems. It is often recognized by the discoloration in the water from the algae's pigments. The term ''algae'' encompass ...
s produce toxins, however, with some only discoloring water, producing a smelly odor, or adding a bad taste to the water. Unfortunately, it is not possible to tell if a bloom is harmful from just appearances, since sampling and microscopic examination is required. In many cases microscopy is not sufficient to tell the difference between toxic and non-toxic populations. In these cases, tools can be employed to measure the toxin level or to determine if the toxin-production genes are present.


Terminology

In a narrow definition, harmful algal blooms are only those blooms that release toxins that affect other species. On the other hand, any algal bloom can cause dead zones due to low oxygen levels, and could therefore be called "harmful" in that sense. The usage of the term "harmful algal blooms" in the media and scientific literature is varied. 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". A harmful algal bloom is "a societal concept rather than a scientific definition". A similarly broad definition of HABs was adopted by the
US Environmental Protection Agency The Environmental Protection Agency (EPA) is an independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it be ...
in 2008 who stated that HABs include "potentially toxic (auxotrophic, heterotrophic) species and high-biomass producers that can cause hypoxia and anoxia and indiscriminant mortalities of marine life after reaching dense concentrations, whether or not toxins are produced".


Red tide

Harmful algal bloom in coastal areas are also often referred to as "red tides". The term "red tide" is derived from blooms of any of several species of
dinoflagellate The dinoflagellates ( Greek δῖνος ''dinos'' "whirling" and Latin ''flagellum'' "whip, scourge") are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered algae. Dinoflagellates are ...
, such as
Karenia brevis ''Karenia brevis'' is a microscopic, single-celled, photosynthetic organism in the genus '' Karenia''. It is a marine dinoflagellate commonly found in the waters of the Gulf of Mexico. It is the organism responsible for the "Florida red tides" ...
. However, the term is misleading since algal blooms can widely vary in color, and growth of algae is unrelated to the
tide Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables ...
s. Not all red tides are produced by dinoflagellates. The
mixotrophic A mixotroph is an organism that can use a mix of different sources of energy and carbon, instead of having a single trophic mode on the continuum from complete autotrophy at one end to heterotrophy at the other. It is estimated that mixotrophs com ...
ciliate '' Mesodinium rubrum'' produces non-toxic blooms coloured deep red by chloroplasts it has enslaved from the algae it eats. As a technical term, it is being replaced in favor of more precise terminology, including the generic term "harmful algal bloom" for harmful species, and "
algal bloom An algal bloom or algae bloom is a rapid increase or accumulation in the population of algae in freshwater or marine water systems. It is often recognized by the discoloration in the water from the algae's pigments. The term ''algae'' encompass ...
" for benign species.


Types

There are three main types of phytoplankton which can form into harmful algal blooms:
cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, bl ...
,
dinoflagellates The dinoflagellates ( Greek δῖνος ''dinos'' "whirling" and Latin ''flagellum'' "whip, scourge") are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered algae. Dinoflagellates ...
and
diatoms A diatom (Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising sev ...
. All three are made up of microscopic floating organisms which, like plants, can create their own food from sunlight by means of
photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in ...
. That ability makes the majority of them an essential part of the
food web A food web is the natural interconnection of food chains and a graphical representation of what-eats-what in an ecological community. Another name for food web is consumer-resource system. Ecologists can broadly lump all life forms into one o ...
for small fish and other organisms.Black, Jacquelyn G., and Black, Laura J. ''Microbiology: Principles and Explorations'', 8th Ed., John Wiley & Sons (2012)


Cyanobacteria

Harmful algal blooms in freshwater lakes and rivers, or at
estuaries An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environme ...
, where rivers flow into the ocean, are caused by cyanobacteria, which are commonly referred to as "blue-green algae",Peebles, Ernst B
"Why toxic algae blooms like Florida’s are so dangerous to people and wildlife"
''Huffington Post'', July 20, 2016
but are in fact prokaryotic bacteria, as opposed to algae which are
eukaryote Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacter ...
s. Some cyanobacteria, including the widespread genus Microsystis, can produce hazardous cyanotoxins such as microcystins,"Are all algal blooms harmful?"
''NOAA'', April 28, 2016
which are hepatotoxins that harm the liver of mammals. Other types of cyanobacteria can also produce hepatoxins, as well as neurotoxins, cytotoxins, and endotoxins.
Water purification Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids, and gases from water. The goal is to produce water that is fit for specific purposes. Most water is purified and disinfected for hu ...
plants may be unable to remove these toxins, leading to increasingly common localised advisories against drinking tap water, as happened in Toledo, Ohio in August 2014. In August 2021, there were 47 lakes confirmed to have algal blooms in New York State alone. In September 2021, Spokane County’s Environmental Programs issued a HAB alert for Newman Lake following tests showing potentially harmful toxicity levels for cyanobacteria, while in the same month record-high levels of microcystins were reported leading to an extended 'Do Not Drink' advisory for 280 households at Clear Lake, California's second-largest freshwater lake. Water conditions in Florida, meanwhile, continue to deteriorate under increasing nutrient inflows, causing severe HAB events in both freshwater and marine areas. HABs also cause harm by blocking the sunlight used by plants and algae to photosynthesise, or by depleting the dissolved oxygen needed by fish and other aquatic animals, which can lead to fish die-offs. When such oxygen-depleted water covers a large area for an extended period of time, it can become hypoxic or even anoxic; these areas are commonly called dead zones. These dead zones can be the result of numerous different factors ranging from natural phenomenon to deliberate human intervention, and are not just limited to large bodies of fresh water as found in the great lakes, but are also prone to bodies of salt water as well.


Dual-stage life systems of algal species

Many of the species that form harmful algae blooms will undergo a dual-stage life system. These species will alternate between a
benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning " ...
resting stage and a
pelagic The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or w ...
vegetative state. The benthic resting stage corresponds to when these species are resting near the ocean floor. In this stage, the species cells are waiting for optimal conditions so that they can move towards the surface. These species will then transition from the benthic resting stage into the pelagic vegetative state - where they are more active and found near the water body surface. In the pelagic vegetative state, these cells are able to grow and multiply. It is within the pelagic vegetative state that a bloom is able to occur - as the cells rapidly reproduce and take over the upper regions of the body of water. The transition between these two life stages can have multiple effects on the algae bloom (such as rapid termination of the HAB as cells convert from the pelagic state to the benthic state). Many of the algal species that undergo this dual-stage life cycle are capable of rapid vertical migration. This migration is required for the movement from the benthic area of bodies of water to the pelagic zone. These species require immense amounts of energy as they pass through the various thermoclines,
halocline In oceanography, a halocline (from Greek ''hals'', ''halos'' 'salt' and ''klinein'' 'to slope') is a cline, a subtype of chemocline caused by a strong, vertical salinity gradient within a body of water. Because salinity (in concert with te ...
s, and pycnoclines that are associated with the bodies of water in which these cells exist.


Diatoms and dinoflagellates (in marine coastal areas)

The other types of algae are
diatom A diatom ( Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising se ...
s and
dinoflagellate The dinoflagellates ( Greek δῖνος ''dinos'' "whirling" and Latin ''flagellum'' "whip, scourge") are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered algae. Dinoflagellates are ...
s, found primarily in marine environments, such as ocean coastlines or bays, where they can also form algal blooms. Coastal HABs are a natural phenomenon,FAQs about red tides
Texas Parks & Wildlife Department
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 Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phyt ...
and/or climate change. They can occur when warmer water, salinity, and nutrients reach certain levels, which then stimulates their growth. Most HAB algae are dinoflagellates.Ryan, John
"Red Tide & HAB Studies in Monterey Bay"
Monterey Bay Sanctuary Advisory Council Meeting, August 15, 2008
They are visible in water at a concentration of 1,000 algae cells/ml, while in dense blooms they can measure over 200,000/ml. Diatoms produce
domoic acid Domoic acid (DA) is a kainic acid-type neurotoxin that causes amnesic shellfish poisoning (ASP). It is produced by algae and accumulates in shellfish, sardines, and anchovies. When sea lions, otters, cetaceans, humans, and other predators eat c ...
, another neurotoxin, which can cause seizures in higher vertebrates and birds as it concentrates up the food chain."Domoic Acid Toxicity"
''The Marine Mammal Center''
Domoic acid readily accumulates in the bodies of
shellfish Shellfish is a colloquial and fisheries term for exoskeleton-bearing aquatic invertebrates used as food, including various species of molluscs, crustaceans, and echinoderms. Although most kinds of shellfish are harvested from saltwater environ ...
,
sardines "Sardine" and "pilchard" are common names for various species of small, oily forage fish in the herring family Clupeidae. The term "sardine" was first used in English during the early 15th century, a folk etymology says it comes from the Ital ...
, and
anchovies An anchovy is a small, common forage fish of the family Engraulidae. Most species are found in marine waters, but several will enter brackish water, and some in South America are restricted to fresh water. More than 140 species are placed in 1 ...
, which if then eaten by sea lions,
otters Otters are carnivorous mammals in the subfamily Lutrinae. The 13 extant otter species are all semiaquatic, aquatic, or marine, with diets based on fish and invertebrates. Lutrinae is a branch of the Mustelidae family, which also includes weas ...
,
cetaceans Cetacea (; , ) is an infraorder of aquatic mammals that includes whales, dolphins, and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively carnivorous diet. They propel th ...
, birds or people, can affect the nervous system causing serious injury or death. In the summer of 2015, the state governments closed important shellfish fisheries in
Washington Washington commonly refers to: * Washington (state), United States * Washington, D.C., the capital of the United States ** A metonym for the federal government of the United States ** Washington metropolitan area, the metropolitan area centered o ...
,
Oregon Oregon () is a U.S. state, state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington (state), Washington, while the Snake River delineates much of it ...
and
California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...
because of high concentrations of domoic acid in shellfish."NOAA Fisheries mobilizes to gauge unprecedented West Coast toxic algal bloom"
Northwest Fisheries Science Center, June 2015
In the marine environment, single-celled, microscopic, plant-like organisms naturally occur in the well-lit surface layer of any body of water. These organisms, referred to as
phytoplankton Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'. ...
or
microalgae Microalgae or microphytes are microscopic algae invisible to the naked eye. They are phytoplankton typically found in freshwater and marine systems, living in both the water column and sediment. They are unicellular species which exist indiv ...
, form the base of the food web upon which nearly all other marine organisms depend. Of the 5000+ species of marine phytoplankton that exist worldwide, about 2% are known to be harmful or toxic. 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.


List of common HAB genera

* '' Gonyaulax'' * '' Karenia'' * '' Gymnodinium'' * '' Dinophysis'' * '' Noctiluca'' * '' Chattonella'' * '' Ceratium'' * '' Amoebophyre'' * ''
Alexandrium Alexandreion (Greek), or Alexandrium (Latin), called Sartaba in the Mishna and Talmud and Qarn Sartaba in Arabic, was an ancient hilltop fortress constructed by the Hasmoneans between Scythopolis and Jerusalem on a pointy barren hill towering ...
'' * ''
Cochlodinium ''Cochlodinium'' is a genus of dinoflagellates belonging to the family Gymnodiniaceae Gymnodiniaceae is a family of dinoflagellates belonging to the order Gymnodiniales. Genera As accepted by GBIF; * ''Akashiwo'' G.Hansen & Moestrup (1) * ...
''


Causes

It is sometimes unclear what causes specific HABs as their occurrence in some locations appears to be entirely natural, while in others they appear to be a result of human activities. Furthermore, there are many different species of algae that can form HABs, each with different environmental requirements for optimal growth. The frequency and severity of HABs in some parts of the world have been linked to increased nutrient loading from human activities. In other areas, HABs are a predictable seasonal occurrence resulting from coastal upwelling, a natural result of the movement of certain ocean currents. 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. The type of nitrates and phosphates available in the system are also a factor, since phytoplankton can grow at different rates depending on the relative abundance of these substances (e.g.
ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous ...
,
urea Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid. Urea serves an important ...
, nitrate ion). A variety of other nutrient sources can also play an important role in affecting algal bloom formation, including iron, silica or carbon. Coastal
water pollution Water pollution (or aquatic pollution) is the contamination of water bodies, usually as a result of human activities, so that it negatively affects its uses. Water bodies include lakes, rivers, oceans, aquifers, reservoirs and groundwater. ...
produced by humans (including iron fertilization) and systematic increase in sea water temperature have also been suggested as possible contributing factors in HABs. Among the causes of algal blooms are: * Excess nutrients—
phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ea ...
and
nitrates Nitrate is a polyatomic ion with the chemical formula . Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are soluble in water. An example of an insolu ...
—from fertilizers or
sewage Sewage (or domestic sewage, domestic wastewater, municipal wastewater) is a type of wastewater that is produced by a community of people. It is typically transported through a sewer system. Sewage consists of wastewater discharged from reside ...
that are discharged to water bodies (also called
nutrient pollution Nutrient pollution, a form of water pollution, refers to contamination by excessive inputs of nutrients. It is a primary cause of eutrophication of surface waters (lakes, rivers and coastal waters), in which excess nutrients, usually nitrogen or ...
) *
climate change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...
*
thermal pollution Thermal pollution, sometimes called "thermal enrichment", is the degradation of water quality by any process that changes ambient water temperature. Thermal pollution is the rise or fall in the temperature of a natural body of water caused by hum ...
from power plants and factories * low water levels in inland waterways and lakes, which reduces water flow and increases water temperatures"Neurotoxic algae bloom that shuts down Utah Lake can affect brain, liver"
''KUTV'', July 15, 2016
"Russian River to be closely monitored this summer to guard against harmful algae blooms"
''Press Democrat'' June 23, 2016
* invasive filter feeders—especially
Zebra mussel The zebra mussel (''Dreissena polymorpha'') is a small freshwater mussel. The species originates from the lakes of southern Russia and Ukraine, but has been accidentally introduced to numerous other areas and has become an invasive species in ma ...
s, ''Dreissena polymorpha''—which preferentially eat non-toxic algae, competitors to harmful algae


Nutrients

Nutrients enter freshwater or marine environments as
surface runoff Surface runoff (also known as overland flow) is the flow of water occurring on the ground surface when excess rainwater, stormwater, meltwater, or other sources, can no longer sufficiently rapidly infiltrate in the soil. This can occur when t ...
from
agricultural pollution Agricultural pollution refers to biotic and abiotic byproducts of farming practices that result in contamination or degradation of the environment and surrounding ecosystems, and/or cause injury to humans and their economic interests. The pol ...
and
urban runoff Urban runoff is surface runoff of rainwater, landscape irrigation, and car washing created by urbanization. Impervious surfaces (roads, parking lots and sidewalks) are constructed during land development. During rain , storms and other precip ...
from fertilized lawns, golf courses and other landscaped properties; and from
sewage treatment plants Sewage treatment (or domestic wastewater treatment, municipal wastewater treatment) is a type of wastewater treatment which aims to remove contaminants from sewage to produce an effluent that is suitable for discharge to the surrounding en ...
that lack nutrient control systems. Additional nutrients are introduced from atmospheric pollution.Miller, G. Tyler Jr., ''Environmental Science'', Thomas Learning (2003) pp. 355357 Coastal areas worldwide, especially wetlands and estuaries, coral reefs and swamps, are prone to being overloaded with those nutrients. Most of the large cities along the
Mediterranean Sea The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on ...
, for example, discharge all of their sewage into the sea untreated. The same is true for most coastal developing countries, while in parts of the developing world, as much as 70% of wastewater from large cities may re-enter water systems without being treated. Residual nutrients in treated wastewater can also accumulate in downstream source water areas and fuel eutrophication, which leads progressively to a cyanobacteria-dominated system characterized by seasonal HABS. As more wastewater treatment infrastructure is built, more treated wastewater is returned to the natural water system, leading to a significant increase in these residual nutrients. Residual nutrients combine with nutrients from other sources to increase the sediment nutrient stockpile that is the driving force behind phase shifts to entrenched eutrophic conditions. This contributes to the ongoing degradation of dams, lakes, rivers, and reservoirs - source water areas that are starting to become known as ecological infrastructure, placing increasing pressure on wastewater treatment works and water purification plants. Such pressures, in turn, intensify seasonal HABs.


Climate change

Climate change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...
contributes to warmer waters which makes conditions more favorable for algae growth in more regions and farther north. In general, still, warm, shallow water, combined with high-nutrient conditions in lakes or rivers, increases the risk of harmful algal blooms. Warming of summer surface temperatures of lakes, which rose by 0.34 °C decade per decade between 1985 and 2009 due to global warming, also will likely increase algal blooming by 20% over the next century. Although the drivers of harmful algal blooms are poorly understood they do appear to have increased in range expansion and frequency in coastal areas since the 1980s.IPCC, 2019
Summary for Policymakers
In
IPCC Special Report on the Ocean and Cryosphere in a Changing Climate
.-O. Pörtner, D.C. Roberts, V. Masson-Delmotte, P. Zhai, M. Tignor, E. Poloczanska, K. Mintenbeck, A. Alegría, M.  Nicolai, A. Okem, J. Petzold, B. Rama, N.M. Weyer (eds.) Cambridge University Press, Cambridge, UK and New York, NY, USA. https://doi.org/10.1017/9781009157964.001.
The is the result of human induced factors such as increased nutrient inputs (
nutrient pollution Nutrient pollution, a form of water pollution, refers to contamination by excessive inputs of nutrients. It is a primary cause of eutrophication of surface waters (lakes, rivers and coastal waters), in which excess nutrients, usually nitrogen or ...
) and climate change (in particular the warming of water temperatures). The parameters that affect the formation of HABs are ocean warming, marine heatwaves, oxygen loss, eutrophication and
water pollution Water pollution (or aquatic pollution) is the contamination of water bodies, usually as a result of human activities, so that it negatively affects its uses. Water bodies include lakes, rivers, oceans, aquifers, reservoirs and groundwater. ...
.


Causes or contributing factors of coastal HABs

HABs contain dense concentrations of organisms and appear as discolored water, often reddish-brown in color. It is a natural phenomenon, but the exact cause or combination of factors that result in a HAB event are not necessarily known. However, three key natural factors are thought to play an important role in a bloom - salinity, temperature, and wind. HABs cause economic harm, so outbreaks are carefully monitored. For example, the
Florida Fish and Wildlife Conservation Commission The Florida Fish and Wildlife Conservation Commission (FWC) is a Florida government agency founded in 1999 and headquartered in Tallahassee. It manages and regulates the state's fish and wildlife resources, and enforces related laws. Officers ar ...
provides an up-to-date status report on HABs in Florida. The
Texas Parks and Wildlife Department The Texas Parks & Wildlife Department (TPWD) is a Texas state agency that oversees and protects wildlife and their habitats. In addition, the agency is responsible for managing the state's parks and historical areas. Its mission is to manage ...
also provides a status report. While no particular cause of HABs has been found, many different factors can contribute to their presence. These factors can include
water pollution Water pollution (or aquatic pollution) is the contamination of water bodies, usually as a result of human activities, so that it negatively affects its uses. Water bodies include lakes, rivers, oceans, aquifers, reservoirs and groundwater. ...
, which originates from sources such as human
sewage Sewage (or domestic sewage, domestic wastewater, municipal wastewater) is a type of wastewater that is produced by a community of people. It is typically transported through a sewer system. Sewage consists of wastewater discharged from reside ...
and agricultural runoff. The occurrence of HABs in some locations appears to be entirely natural (algal blooms are a seasonal occurrence resulting from coastal upwelling, a natural result of the movement of certain ocean currents) while in others they appear to be a result of increased
nutrient pollution Nutrient pollution, a form of water pollution, refers to contamination by excessive inputs of nutrients. It is a primary cause of eutrophication of surface waters (lakes, rivers and coastal waters), in which excess nutrients, usually nitrogen or ...
from human activities. The growth of marine phytoplankton is generally limited by the availability of
nitrates Nitrate is a polyatomic ion with the chemical formula . Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are soluble in water. An example of an insolu ...
and
phosphates In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid . The phosphate or orthophosphate ion is derived from phosph ...
, which can be abundant in agricultural run-off as well as coastal upwelling zones. Other factors such as iron-rich dust influx from large desert areas such as the Sahara Desert are thought to play a major role in causing HAB events. Some algal blooms on the Pacific Coast have also been linked to occurrences of large-scale climatic oscillations such as
El Niño El Niño (; ; ) is the warm phase of the El Niño–Southern Oscillation (ENSO) and is associated with a band of warm ocean water that develops in the central and east-central equatorial Pacific (approximately between the International Date ...
events.


Other causes

Other factors such as iron-rich dust influx from large desert areas such as the
Sahara , photo = Sahara real color.jpg , photo_caption = The Sahara taken by Apollo 17 astronauts, 1972 , map = , map_image = , location = , country = , country1 = , ...
are thought to play a role in causing HABs. Some algal blooms on the
Pacific coast Pacific coast may be used to reference any coastline that borders the Pacific Ocean. Geography Americas Countries on the western side of the Americas have a Pacific coast as their western or southwestern border, except for Panama, where the Pac ...
have also been linked to natural occurrences of large-scale climatic oscillations such as
El Niño El Niño (; ; ) is the warm phase of the El Niño–Southern Oscillation (ENSO) and is associated with a band of warm ocean water that develops in the central and east-central equatorial Pacific (approximately between the International Date ...
events. HABs are also linked to heavy rainfall. Although HABs in the Gulf of Mexico were witnessed in the early 1500s by explorer
Cabeza de Vaca In Mexican cuisine, ''cabeza'' (''lit.'' 'head') is the meat from a roasted head of an animal, served as taco A taco (, , ) is a traditional Mexican food consisting of a small hand-sized corn- or wheat-based tortilla topped with a filling ...
, it is unclear what initiates these blooms and how large a role
anthropogenic Anthropogenic ("human" + "generating") is an adjective that may refer to: * Anthropogeny, the study of the origins of humanity Counterintuitively, anthropogenic may also refer to things that have been generated by humans, as follows: * Human i ...
and natural factors play in their development.


Number and sizes

The number of reported harmful algal blooms (cyanobacterial) has been increasing throughout the world. It is unclear whether the apparent increase in frequency and severity of HABs in various parts of the world is in fact a real increase or is due to increased observation effort and advances in species identification technology. In 2008, the U.S. government prepared a report on the problem, "Harmful Algal Bloom Management and Response: Assessment and Plan"."Harmful Algal Bloom Management and Response: Assessment and Plan"
, Office of Science and Technology Policy, Sept. 2008
The report recognized the seriousness of the problem: Researchers have reported the growth of HABs in Europe, Africa and Australia. Those have included blooms on some of the
African Great Lakes The African Great Lakes ( sw, Maziwa Makuu; rw, Ibiyaga bigari) are a series of lakes constituting the part of the Rift Valley lakes in and around the East African Rift. They include Lake Victoria, the second-largest fresh water lake in th ...
, such as
Lake Victoria Lake Victoria is one of the African Great Lakes. With a surface area of approximately , Lake Victoria is Africa's largest lake by area, the world's largest tropical lake, and the world's second-largest fresh water lake by surface area after ...
, the second largest freshwater lake in the world.
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...
has been reporting an increase in the number of blooms each year. In 1977
Hong Kong Hong Kong ( (US) or (UK); , ), officially the Hong Kong Special Administrative Region of the People's Republic of China (abbr. Hong Kong SAR or HKSAR), is a List of cities in China, city and Special administrative regions of China, special ...
reported its first coastal HAB. By 1987 they were getting an average of 35 per year. Additionally, there have been reports of harmful algal blooms throughout popular Canadian lakes such as Beaver Lake and Quamichan Lake. These blooms were responsible for the deaths of a few animals and led to swimming advisories. Global warming and pollution is causing algal blooms to form in places previously considered "impossible" or rare for them to exist, such as under the ice sheets in the
Arctic The Arctic ( or ) is a polar regions of Earth, polar region located at the northernmost part of Earth. The Arctic consists of the Arctic Ocean, adjacent seas, and parts of Canada (Yukon, Northwest Territories, Nunavut), Danish Realm (Greenla ...
, in
Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...
, the Himalayan Mountains, the
Rocky Mountains The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in straight-line distance from the northernmost part of western Canada, to New Mexico ...
, and in the
Sierra Nevada Mountains The Sierra Nevada () is a mountain range in the Western United States, between the Central Valley of California and the Great Basin. The vast majority of the range lies in the state of California, although the Carson Range spur lies primarily ...
. In the U.S., every coastal state has had harmful algal blooms over the last decade and new species have emerged in new locations that were not previously known to have caused problems. Inland, major rivers have seen an increase in their size and frequency. In 2015 the
Ohio River The Ohio River is a long river in the United States. It is located at the boundary of the Midwestern and Southern United States, flowing southwesterly from western Pennsylvania to its mouth on the Mississippi River at the southern tip of ...
had a bloom which stretched an "unprecedented" into adjoining states and tested positive for toxins, which created drinking water and recreation problems. A portion of Utah's
Jordan River The Jordan River or River Jordan ( ar, نَهْر الْأُرْدُنّ, ''Nahr al-ʾUrdunn'', he, נְהַר הַיַּרְדֵּן, ''Nəhar hayYardēn''; syc, ܢܗܪܐ ܕܝܘܪܕܢܢ ''Nahrāʾ Yurdnan''), also known as ''Nahr Al-Shariea ...
was closed due to toxic algal bloom in 2016. Off the west coast of
South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring coun ...
, HABs caused by '' Alexandrium catanella'' occur every spring. These blooms of organisms cause severe disruptions in
fisheries Fishery can mean either the enterprise of raising or harvesting fish and other aquatic life; or more commonly, the site where such enterprise takes place ( a.k.a. fishing ground). Commercial fisheries include wild fisheries and fish farms, ...
of these waters as the toxins in the phytoplankton cause filter-feeding
shellfish Shellfish is a colloquial and fisheries term for exoskeleton-bearing aquatic invertebrates used as food, including various species of molluscs, crustaceans, and echinoderms. Although most kinds of shellfish are harvested from saltwater environ ...
in affected waters to become poisonous for human consumption.


Harmful effects

As algal blooms grow, they deplete the oxygen in the water and block sunlight from reaching fish and plants. Such blooms can last from a few days to many months. With less light, plants beneath the bloom can die and fish can starve. Furthermore, the dense population of a bloom reduces oxygen saturation during the night by respiration. And when the algae eventually die off, the microbes which decompose the dead algae use up even more oxygen, which in turn causes more fish to die or leave the area. When oxygen continues to be depleted by blooms it can lead to hypoxic dead zones, where neither fish nor plants are able to survive. These dead zones in the case of the Chesapeake Bay, where they are a normal occurrence, are also suspected of being a major source of
methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane ...
. Scientists have found that HABs were a prominent feature of previous mass
extinction event An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp change in the diversity and abundance of multicellular organisms. I ...
s, including the End-Permian Extinction.


Human health

Tests have shown some toxins near blooms can be in the air and thereby be inhaled, which could affect health.


Food

Eating fish or shellfish from lakes with a bloom nearby is not recommended. Potent toxins are accumulated in shellfish that feed on the algae. If the shellfish are consumed, various types of poisoning may result. These include
amnesic shellfish poisoning Amnesic shellfish poisoning (ASP) is an illness caused by consumption of shellfish that contain the marine biotoxin called domoic acid. In mammals, including humans, domoic acid acts as a neurotoxin, causing permanent short-term memory loss, bra ...
(ASP),
diarrhetic shellfish poisoning Diarrhetic shellfish poisoning (DSP) is one of the four recognized symptom types of shellfish poisoning, the others being paralytic shellfish poisoning, neurotoxic shellfish poisoning and amnesic shellfish poisoning. As the name suggests, this sy ...
, neurotoxic shellfish poisoning, and
paralytic shellfish poisoning Paralytic shellfish poisoning (PSP) is one of the four recognized syndromes of shellfish poisoning, which share some common features and are primarily associated with bivalve mollusks (such as mussels, clams, oysters and scallops). These shellfi ...
.A 2002 study has shown that algal toxins may be the cause for as many as 60,000 intoxication cases in the world each year. In 1987 a new illness emerged:
amnesic shellfish poisoning Amnesic shellfish poisoning (ASP) is an illness caused by consumption of shellfish that contain the marine biotoxin called domoic acid. In mammals, including humans, domoic acid acts as a neurotoxin, causing permanent short-term memory loss, bra ...
(ASP). People who had eaten
mussel Mussel () is the common name used for members of several families of bivalve molluscs, from saltwater and freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other edible clams, which ...
s from
Prince Edward Island Prince Edward Island (PEI; ) is one of the thirteen provinces and territories of Canada. It is the smallest province in terms of land area and population, but the most densely populated. The island has several nicknames: "Garden of the Gulf", ...
were found to have ASP. The illness was caused by
domoic acid Domoic acid (DA) is a kainic acid-type neurotoxin that causes amnesic shellfish poisoning (ASP). It is produced by algae and accumulates in shellfish, sardines, and anchovies. When sea lions, otters, cetaceans, humans, and other predators eat c ...
, produced by a diatom found in the area where the mussels were cultivated. A 2013 study found that toxic
paralytic shellfish poisoning Paralytic shellfish poisoning (PSP) is one of the four recognized syndromes of shellfish poisoning, which share some common features and are primarily associated with bivalve mollusks (such as mussels, clams, oysters and scallops). These shellfi ...
in the
Philippines The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no), * bik, Republika kan Filipinas * ceb, Republika sa Pilipinas * cbk, República de Filipinas * hil, Republ ...
during HABs has caused at least 120 deaths over a few decades. After a 2014 HAB incident in
Monterey Bay Monterey Bay is a bay of the Pacific Ocean located on the coast of the U.S. state of California, south of the San Francisco Bay Area and its major city at the south of the bay, San Jose. San Francisco itself is further north along the coast, by ...
, California, health officials warned people not to eat certain parts of anchovy, sardines, or crab caught in the bay. In 2015 most shellfish fisheries in Washington, Oregon and California were shut down because of high concentrations of toxic domoic acid in shellfish. People have been warned that inhaling vapors from waves or wind during a HAB event may cause asthma attacks or lead to other respiratory ailments. In 2018 agricultural officials in
Utah Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to its ...
worried that even crops could become contaminated if irrigated with toxic water, although they admit that they can't measure contamination accurately because of so many variables in farming. They issued warnings to residents, however, out of caution.


Drinking water

Persons are generally warned not to enter or drink water from algal blooms, or let their pets swim in the water since many pets have died from algal blooms. In at least one case, people began getting sick before warnings were issued. There is no treatment available for animals, including livestock cattle, if they drink from algal blooms where such toxins are present. Pets are advised to be kept away from algal blooms to avoid contact. In some locations visitors have been warned not to even touch the water. Boaters have been told that toxins in the water can be inhaled from the spray from wind or waves. Ocean beaches, lakes and rivers have been closed due to algal blooms."Utah County portion of Jordan River closed due to toxic algal bloom"
, ''Daily Herald'', July 21, 2016
After a dog died in 2015 from swimming in a bloom in California's Russian River, officials likewise posted warnings for parts of the river. Boiling the water at home before drinking does not remove the toxins. In August 2014 the city of
Toledo, Ohio Toledo ( ) is a city in and the county seat of Lucas County, Ohio, United States. A major Midwestern United States port city, Toledo is the fourth-most populous city in the state of Ohio, after Columbus, Ohio, Columbus, Cleveland, and Cincinnat ...
advised its 500,000 residents to not drink tap water as the high toxin level from an algal bloom in western
Lake Erie Lake Erie ( "eerie") is the fourth largest lake by surface area of the five Great Lakes in North America and the eleventh-largest globally. It is the southernmost, shallowest, and smallest by volume of the Great Lakes and therefore also ha ...
had affected their water treatment plant's ability to treat the water to a safe level."Toxic Algae Bloom Leaves 500,000 Without Drinking Water in Ohio"
''Ecowatch'', August 3, 2014
The emergency required using bottled water for all normal uses except showering, which seriously affected public services and commercial businesses. The bloom returned in 2015 and was forecast again for the summer of 2016. In 2004, a bloom in Kisumu Bay, which is the drinking water source for 500,000 people in
Kisumu Kisumu ( ) is the third-largest city in Kenya after the capital, Nairobi, and the coastal city of Mombasa (census 2019). It is the third-largest city after Kampala and Mwanza in the Lake Victoria Basin. Apart from being an important p ...
,
Kenya ) , national_anthem = " Ee Mungu Nguvu Yetu"() , image_map = , map_caption = , image_map2 = , capital = Nairobi , coordinates = , largest_city = Nairobi , ...
, suffered from similar water contamination."World Stands By As Algae and Dead Zones Ruin Water"
''Circle of Blue'', Sept. 25, 2014
In China, water was cut off to residents in 2007 due to an algal bloom in its third largest lake, which forced 2 million people to use bottled water. A smaller water shut-down in China affected 15,000 residents two years later at a different location. Australia in 2016 also had to cut off water to farmers. Alan Steinman of
Grand Valley State University Grand Valley State University (GVSU, GV, or Grand Valley) is a public university in Allendale, Michigan. It was established in 1960 as Grand Valley State College. Its main campus is situated on approximately west of Grand Rapids. The universit ...
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. Lake Erie is more prone to blooms because it has a high nutrient level and is shallow, which causes it to warm up more quickly during the summer. Symptoms from drinking toxic water can show up within a few hours after exposure. They can include nausea, vomiting, and diarrhea, or trigger headaches and gastrointestinal problems. Although rare, liver toxicity can cause death. Those symptoms can then lead to dehydration, another major concern. In high concentrations, the toxins in the algal waters when simply touched can cause skin rashes, irritate the eyes, nose, mouth or throat. Those with suspected symptoms are told to call a doctor if symptoms persist or they can't hold down fluids after 24 hours. In studies at the population level bloom coverage has been significantly related to the risk of non-alcoholic
liver disease Liver disease, or hepatic disease, is any of many diseases of the liver. If long-lasting it is termed chronic liver disease. Although the diseases differ in detail, liver diseases often have features in common. Signs and symptoms Some of the si ...
death.


Neurological disorders

Toxic algae blooms are thought to play a role in humans developing degenerative neurological disorders such as
amyotrophic lateral sclerosis Amyotrophic lateral sclerosis (ALS), also known as motor neuron disease (MND) or Lou Gehrig's disease, is a neurodegenerative disease that results in the progressive loss of motor neurons that control voluntary muscles. ALS is the most commo ...
and
Parkinson's disease Parkinson's disease (PD), or simply Parkinson's, is a long-term degenerative disorder of the central nervous system that mainly affects the motor system. The symptoms usually emerge slowly, and as the disease worsens, non-motor symptoms beco ...
. Less than one percent of algal blooms produce hazardous toxins, such as microcystins. Although blue-green or other algae do not usually pose a direct threat to health, the
toxins A toxin is a naturally occurring organic poison produced by metabolic activities of living cells or organisms. Toxins occur especially as a protein or conjugated protein. The term toxin was first used by organic chemist Ludwig Brieger (1849� ...
(poisons) which they produce are considered dangerous to humans, land animals, sea mammals, birds and fish when the toxins are ingested. The toxins are
neurotoxins Neurotoxins are toxins that are destructive to nerve tissue (causing neurotoxicity). Neurotoxins are an extensive class of exogenous chemical neurological insultsSpencer 2000 that can adversely affect function in both developing and mature nerv ...
which destroy nerve tissue which can affect the nervous system, brain, and liver, and can lead to death.


Effects on humans from harmful algal blooms in marine environments

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. The brevetoxins bind to voltage-gated sodium channels, important structures of cell membranes. Binding results in persistent activation of nerve cells, which interferes with neural transmission leading to health problems. These toxins are created within the unicellular organism, or as a metabolic product. The two major types of brevetoxin compounds have similar but distinct backbone structures. PbTx-2 is the primary intracellular brevetoxin produced by ''K. brevis'' blooms. However, over time, the PbTx-2 brevetoxin can be converted to PbTx-3 through metabolic changes. Researchers found that PbTx-2 has been the primary intracellular brevetoxin that converts over time into PbTx-3. In the U.S., the seafood consumed by humans is tested regularly for toxins by the USDA to ensure safe consumption. Such testing is common in other nations. However, improper harvesting of shellfish can cause
paralytic shellfish poisoning Paralytic shellfish poisoning (PSP) is one of the four recognized syndromes of shellfish poisoning, which share some common features and are primarily associated with bivalve mollusks (such as mussels, clams, oysters and scallops). These shellfi ...
and neurotoxic shellfish poisoning in humans. Some symptoms include drowsiness, diarrhea, nausea, loss of motor control, tingling, numbing or aching of extremities, incoherence, and respiratory paralysis. Reports of skin irritation after swimming in the ocean during a HAB are common. When the HAB cells rupture, they release extracellular brevetoxins into the environment. Some of those stay in the ocean, while other particles get aerosolized. During onshore winds, brevetoxins can become aerosolized by bubble-mediated transport, causing respiratory irritation,
bronchoconstriction Bronchoconstriction is the constriction of the airways in the lungs due to the tightening of surrounding smooth muscle, with consequent coughing, wheezing, and shortness of breath. Causes The condition has a number of causes, the most common be ...
, coughing, and wheezing, among other symptoms.Backer et al., Lorraine C., Laura E. Flemming, Alan Rowan. "Recreational exposure to aerosolized brevetoxins during Florida red tide events." Harmful Algae 2 (2003): 19–28. 6 March 2018. It is recommended to avoid contact with wind-blown aerosolized toxin. Some individuals report a decrease in respiratory function after only 1 hour of exposure to a ''K. brevis'' red-tide beach and these symptoms may last for days. People with severe or persistent respiratory conditions (such as chronic lung disease or asthma) may experience stronger adverse reactions. There is no known treatment for conditions caused by exposure to a HAB. In most cases patients just wait for the toxin to flush itself out of their system, but in severe cases life support systems may be needed. The
National Oceanic and Atmospheric Administration The National Oceanic and Atmospheric Administration (abbreviated as NOAA ) is an United States scientific and regulatory agency within the United States Department of Commerce that forecasts weather, monitors oceanic and atmospheric conditi ...
's
National Ocean Service The National Ocean Service (NOS) is an office within the U.S. Department of Commerce National Oceanic and Atmospheric Administration (NOAA). It is responsible for preserving and enhancing the nation's coastal resources and ecosystems along the ...
provides a public conditions report identifying possible respiratory irritation impacts in areas affected by HABs.


Economic impact


Recreation and tourism

The hazards which accompany harmful algal blooms have hindered visitors' enjoyment of beaches and lakes in places in the U.S. such as Florida,"Summer Heat Could Worsen Algae Blooms In Florida Waters"
''WLRN'', July 14, 2016
California,
''Los Angeles Times'', July 21, 2016
Vermont, and Utah. Persons hoping to enjoy their vacations or days off have been kept away to the detriment of local economies. Lakes and rivers in
North Dakota North Dakota () is a U.S. state in the Upper Midwest, named after the indigenous Dakota Sioux. North Dakota is bordered by the Canadian provinces of Saskatchewan and Manitoba to the north and by the U.S. states of Minnesota to the east, ...
,
Minnesota Minnesota () is a state in the upper midwestern region of the United States. It is the 12th largest U.S. state in area and the 22nd most populous, with over 5.75 million residents. Minnesota is home to western prairies, now given over t ...
, Utah, California and Ohio have had signs posted warning about the potential of health risk. Similar blooms have become more common in Europe, with France among the countries reporting them. In the summer of 2009, beaches in northern
Brittany Brittany (; french: link=no, Bretagne ; br, Breizh, or ; Gallo: ''Bertaèyn'' ) is a peninsula, historical country and cultural area in the west of modern France, covering the western part of what was known as Armorica during the period ...
became covered by tonnes of potentially lethal rotting green algae. A horse being ridden along the beach collapsed and died from fumes given off by the rotting algae. The economic damage resulting from lost business has become a serious concern. According to one report in 2016, the four main economic impacts from harmful algal blooms come from damage to human health, fisheries, tourism and recreation, and the cost of monitoring and management of area where blooms appear. EPA estimates that algal blooms impact 65 percent of the country's major estuaries, with an annual cost of $2.2 billion. In the U.S. there are an estimated 166 coastal dead zones. 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."Algal bloom and its economic impact"
''European Commission Joint Research Centre'', 2016
In port cities in the
Shandong Province Shandong ( , ; ; alternately romanized as Shantung) is a coastal province of the People's Republic of China and is part of the East China region. Shandong has played a major role in Chinese history since the beginning of Chinese civilizatio ...
of eastern China, residents are no longer surprised when massive algal blooms arrive each year and inundate beaches. Prior to the Beijing Olympics in 2008, over 10,000 people worked to clear 20,000 tons of dead algae from beaches."China: Yellow Sea turns green as Qingdao beaches are covered in algae"
''International Business Times'', July 7, 2015
In 2013 another bloom in China, thought to be its largest ever, covered an area of 7,500 square miles, and was followed by another in 2015 which blanketed an even greater 13,500 square miles. The blooms in China are thought to be caused by pollution from untreated agricultural and industrial discharges into rivers leading to the ocean.


Fisheries industry

As early as 1976 a short-term, relatively small, dead zone off the coasts of
New York New York most commonly refers to: * New York City, the most populous city in the United States, located in the state of New York * New York (state), a state in the northeastern United States New York may also refer to: Film and television * '' ...
and
New Jersey New Jersey is a state in the Mid-Atlantic and Northeastern regions of the United States. It is bordered on the north and east by the state of New York; on the east, southeast, and south by the Atlantic Ocean; on the west by the Delawa ...
cost commercial and recreational fisheries over $500 million."Oceanic Dead Zones Continue to Spread"
''Scientific American'', August 15, 2008
In 1998 a HAB in Hong Kong killed over $10 million in high-value fish.Brown, Lester; McGinn, Anne Platt. ''Vital Signs 1999–2000: The Environmental Trends that Are Shaping Our Future'', Routledge (1999 pp. 198–199 In 2009, the economic impact for the state of Washington's coastal counties dependent on its fishing industry was estimated to be $22 million. In 2016, the U.S. seafood industry expected future lost revenue could amount to $900 million annually. NOAA has provided a few cost estimates for various blooms over the past few years: $10.3 million in 2011 due to a HAB at Texas oyster landings; $2.4 million lost income by tribal commerce from 2015 fishery closures in the pacific northwest; $40 million from Washington state's loss of tourism from the same fishery closure. Along with damage to businesses, the toll from human sickness results in lost wages and damaged health. The costs of medical treatment, investigation by health agencies through water sampling and testing, and the posting of warning signs at effected locations is also costly."Estimated Annual Economic Impacts from Harmful Algal Blooms (HABs) in the United States"
Woods Hole Oceanographic Institution, September 2000
The closures applied to areas where this algae bloom occurs has a big negative impact of the fishing industries, add to that the high fish mortality that follows, the increase in price due to the shortage of fish available and decrease in the demand for seafood due to the fear of contamination by toxins. This causes a big economic loss for the industry. Economic costs are estimated to rise. In June 2015, for instance, the largest known toxic HAB forced the shutdown of the west coast shellfish industry, the first time that has ever happened. One Seattle NOAA expert commented, "This is unprecedented in terms of the extent and magnitude of this harmful algal bloom and the warm water conditions we're seeing offshore...."
''Oregon Live'', June 16, 2015
The bloom covered a range from
Santa Barbara, California Santa Barbara ( es, Santa Bárbara, meaning " Saint Barbara") is a coastal city in Santa Barbara County, California, of which it is also the county seat. Situated on a south-facing section of coastline, the longest such section on the West ...
northward to
Alaska Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U ...
. The negative impact on fish can be even more severe when they are confined to pens, as they are in fish farms. In 2007 a fish farm in
British Columbia British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, for ...
lost 260 tons of salmon as a result of blooms, and in 2016 a farm in Chile lost 23 million salmon after an algal bloom.


Environmental impact


Dead zones

The presence of harmful algae bloom’s can lead to hypoxia or anoxia in a body of water. The depletion of oxygen within a body of water can lead to the creation of a dead zone. Dead zones occur when a body of water has become unsuitable for organism survival in that location. HAB’s cause dead zones by consuming oxygen in these bodies of water - leaving minimal oxygen available to other marine organisms. When the HAB’s die, their bodies will sink to the bottom of the body of water - as the decaying of their bodies (through bacteria) is what causes the consumption of oxygen. Once oxygen levels get so low, the HAB’s have placed the body of water in hypoxia - and these low oxygen levels will cause marine organisms to seek out better suited locations for their survival. Blooms can harm the environment even without producing toxins by depleting oxygen from the water when growing and while decaying after they die. Blooms can also block sunlight to organisms living beneath it. A record-breaking number and size of blooms have formed in the Pacific coast, in Lake Erie, in the Chesapeake Bay and in the Gulf of Mexico, where a number of dead zones were created as a result."Toxic Algal Blooms Aren’t Just Florida’s Problem. And They’re On The Rise."
''Huffington Post'', July 7, 2016
In the 1960s the number of dead zones worldwide was 49; the number rose to over 400 by 2008. Among the largest dead zones were those in northern Europe’s
Baltic Sea The Baltic Sea is an arm of the Atlantic Ocean that is enclosed by Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden and the North and Central European Plain. The sea stretches from 53°N to 66°N latitude and from ...
and the Gulf of Mexico, which affects a $2.8 billion U.S. fish industry. Unfortunately, dead zones rarely recover and usually grow in size. One of the few dead zones to ever recover was in the
Black Sea The Black Sea is a marginal mediterranean sea of the Atlantic Ocean lying between Europe and Asia, east of the Balkans, south of the East European Plain, west of the Caucasus, and north of Anatolia. It is bounded by Bulgaria, Georgia, Rom ...
, which returned to normal fairly quickly after the collapse of the Soviet Union in the 1990s due to a resulting reduction in fertilizer use.


Fish die-offs

Massive fish die-offs have been caused by HABs."Fish Kills due to Harmful Algal Blooms"
''Woods Hole Oceanographic Institute''
In 2016, 23 million salmon which were being farmed in Chile died from a toxic algae bloom.
''EcoWatch'', March 10, 2016
To get rid of the dead fish, the ones fit for consumption were made into fishmeal and the rest were dumped 60 miles offshore to avoid risks to human health. The economic cost of that die-off is estimated to have been $800 million. Environmental expert Lester Brown has written that the farming of salmon and shrimp in offshore ponds concentrates waste, which contributes to
eutrophication Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phyt ...
and the creation of dead zones. Other countries have reported similar impacts, with cities such as
Rio de Janeiro Rio de Janeiro ( , , ; literally 'River of January'), or simply Rio, is the capital of the state of the same name, Brazil's third-most populous state, and the second-most populous city in Brazil, after São Paulo. Listed by the GaWC as a b ...
, Brazil seeing major fish die-offs from blooms becoming a common occurrence."Brazil removes 50 tons of dead fish from Olympic waters"
''Aljazeera'', April 21, 2015
In early 2015, Rio collected an estimated 50 tons of dead fish from the lagoon where water events in the 2016 Olympics were planned to take place. The
Monterey Bay Monterey Bay is a bay of the Pacific Ocean located on the coast of the U.S. state of California, south of the San Francisco Bay Area and its major city at the south of the bay, San Jose. San Francisco itself is further north along the coast, by ...
has suffered from harmful algal blooms, most recently in 2015: "Periodic blooms of toxin-producing ''
Pseudo-nitzschia ''Pseudo-nitzschia'' is a marine planktonic diatom genus that accounts for 4.4% of pennate diatoms found worldwide. Some species are capable of producing the neurotoxin domoic acid (DA), which is responsible for the neurological disorder in huma ...
'' diatoms have been documented for over 25 years in Monterey Bay and elsewhere along the U.S. west coast. During large blooms, the toxin accumulates in shellfish and small fish such as anchovies and sardines that feed on algae, forcing the closure of some fisheries and poisoning marine mammals and birds that feed on contaminated fish." Similar fish die-offs from toxic algae or lack of oxygen have been seen in Russia, Colombia, Vietnam, China, Canada, Turkey, Indonesia, and France.


Land animal deaths

Land animals, including livestock and pets have been affected. Dogs have died from the toxins after swimming in algal blooms. Warnings have come from government agencies in the state of Ohio, which noted that many dogs and livestock deaths resulted from HAB exposure in the U.S. and other countries. They also noted in a 2003 report that during the previous 30 years, they have seen more frequent and longer-lasting harmful algal blooms.""Harmful Algal Blooms Can Be Deadly to Pets and Livestock"
''Ohio Environmental Protection Agency''
In 50 countries and 27 states that year there were reports of human and animal illnesses linked to algal toxins. In Australia, the department of agriculture warned farmers that the toxins from a HAB had the "potential to kill large numbers of livestock very quickly." Marine mammals have also been seriously harmed, as over 50 percent of unusual marine mammal deaths are caused by harmful algal blooms. In 1999, over 65 bottlenose dolphins died during a coastal HAB in Florida. In 2013 a HAB in southwest Florida killed a record number of
Manatee Manatees (family Trichechidae, genus ''Trichechus'') are large, fully aquatic, mostly herbivorous marine mammals sometimes known as sea cows. There are three accepted living species of Trichechidae, representing three of the four living speci ...
. Whales have also died in large numbers. During the period from 2005 to 2014, Argentina reported an average 65 baby whales dying which experts have linked to algal blooms. A whale expert there expects the whale population to be reduced significantly. In 2003 off
Cape Cod Cape Cod is a peninsula extending into the Atlantic Ocean from the southeastern corner of mainland Massachusetts, in the northeastern United States. Its historic, maritime character and ample beaches attract heavy tourism during the summer mont ...
in the North Atlantic, at least 12 humpback whales died from toxic algae from a HAB. In 2015 Alaska and British Columbia reported many
humpback whales The humpback whale (''Megaptera novaeangliae'') is a species of baleen whale. It is a rorqual (a member of the family Balaenopteridae) and is the only species in the genus ''Megaptera''. Adults range in length from and weigh up to . The humpb ...
had likely died from HAB toxins, with 30 having washed ashore in Alaska. "Our leading theory at this point is that the harmful algal bloom has contributed to the deaths," said a NOAA spokesperson. Birds have died after eating dead fish contaminated with toxic algae. Rotting and decaying fish are eaten by birds such as pelicans,
seagulls Gulls, or colloquially seagulls, are seabirds of the family Laridae in the suborder Lari. They are most closely related to the terns and skimmers and only distantly related to auks, and even more distantly to waders. Until the 21st century, ...
,
cormorant Phalacrocoracidae is a family of approximately 40 species of aquatic birds commonly known as cormorants and shags. Several different classifications of the family have been proposed, but in 2021 the IOC adopted a consensus taxonomy of seven ge ...
s, and possibly marine or land mammals, which then become poisoned. The nervous systems of dead birds were examined and had failed from the toxin's effect. On the Oregon and Washington coast, a thousand
scoter The scoters are stocky seaducks in the genus ''Melanitta''. The drakes are mostly black and have swollen bills, the females are brown. They breed in the far north of Europe, Asia, and North America, and winter farther south in temperate zone ...
s, or sea ducks, were also killed in 2009. "This is huge," said a University professor."Foam from ocean algae bloom killing thousands of birds"
''Oregon Live'', October 22, 2009
As dying or dead birds washed up on the shore, wildlife agencies went into "an emergency crisis mode." It has even been suggested that harmful algal blooms are responsible for the deaths of animals found in fossil troves.


Effects on marine ecosystems

Harmful algal blooms in marine ecosystems have been observed to cause adverse effects to a wide variety of aquatic organisms, most notably marine mammals, sea turtles, seabirds and finfish. The impacts of HAB toxins on these groups can include harmful changes to their developmental, immunological, neurological, or reproductive capacities. The most conspicuous effects of HABs on marine wildlife are large-scale mortality events associated with toxin-producing blooms. 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 Menhaden, also known as mossbunker and bunker and "the most important fish in the sea", are forage fish of the genera ''Brevoortia'' and ''Ethmidium'', two genera of marine fish in the family Clupeidae. ''Menhaden'' is a blend of ''poghaden' ...
with high levels of brevetoxin. Manatee mortalities have also been attributed to brevetoxin but unlike dolphins, the main toxin vector was endemic seagrass species (''Thalassia testudinum'') in which high concentrations of brevetoxins were detected and subsequently found as a main component of the stomach contents of manatees. Additional marine mammal species, like the highly endangered
North Atlantic right whale The North Atlantic right whale (''Eubalaena glacialis'') is a baleen whale, one of three right whale species belonging to the genus '' Eubalaena'', all of which were formerly classified as a single species. Because of their docile nature, their s ...
, have been exposed to neurotoxins by preying on highly contaminated
zooplankton Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...
.Durbin E et al. (2002) North Atlantic right whale, ''Eubalaena glacialis'', exposed to paralytic shellfish poisoning (PSP) toxins by a zooplankton vector, ''Calanus finmarchicus''. Harmful Algae I, : 243–251 (2002) With the summertime habitat of this species overlapping with seasonal blooms of the toxic dinoflagellate ''Alexandrium fundyense'', and subsequent copepod grazing, foraging right whales will ingest large concentrations of these contaminated
copepods Copepods (; meaning "oar-feet") are a group of small crustaceans found in nearly every freshwater and saltwater habitat. Some species are planktonic (inhabiting sea waters), some are benthic (living on the ocean floor), a number of species have p ...
. Ingestion of such contaminated prey can affect respiratory capabilities, feeding behavior, and ultimately the reproductive condition of the population. Immune system responses have been affected by brevetoxin exposure in another critically endangered species, the
loggerhead sea turtle The loggerhead sea turtle (''Caretta caretta'') is a species of oceanic turtle distributed throughout the world. It is a marine reptile, belonging to the family Cheloniidae. The average loggerhead measures around in carapace length when fully ...
. Brevetoxin exposure, from inhalation of aerosolized toxins and ingestion of contaminated prey, can have clinical signs of increased lethargy and muscle weakness in loggerhead sea turtles causing these animals to wash ashore in a decreased metabolic state with increases of immune system responses upon blood analysis. Examples of common harmful effects of HABs include: # the production of neurotoxins which cause mass mortalities in fish, seabirds, sea turtles, and marine mammals # human illness or death from consumption of seafood contaminated by toxic algae # mechanical damage to other organisms, such as disruption of epithelial gill tissues in fish, resulting in asphyxiation # oxygen depletion of the water column (hypoxia or anoxia) from cellular respiration and bacterial degradation


Marine life exposure

HABs occur naturally off coasts all over the world. Marine dinoflagellates produce ichthyotoxins. Where HABs occur, dead fish wash up on shore for up to two weeks after a HAB has been through the area. In addition to killing fish, the toxic algae contaminate shellfish. Some mollusks are not susceptible to the toxin, and store it in their fatty tissues. By consuming the organisms responsible for HABs, shellfish can accumulate and retain
saxitoxin Saxitoxin (STX) is a potent neurotoxin and the best-known paralytic shellfish toxin (PST). Ingestion of saxitoxin by humans, usually by consumption of shellfish contaminated by toxic algal blooms, is responsible for the illness known as paralyti ...
produced by these organisms. Saxitoxin blocks
sodium channel Sodium channels are integral membrane proteins that form ion channels, conducting sodium ions (Na+) through a cell's membrane. They belong to the superfamily of cation channels and can be classified according to the trigger that opens the chan ...
s and ingestion can cause
paralysis Paralysis (also known as plegia) is a loss of motor function in one or more muscles. Paralysis can also be accompanied by a loss of feeling (sensory loss) in the affected area if there is sensory damage. In the United States, roughly 1 in 5 ...
within 30 minutes. In addition to directly harming marine animals and vegetation loss, harmful algal blooms can also lead to
ocean acidification Ocean acidification is the reduction in the pH value of the Earth’s ocean. Between 1751 and 2021, the average pH value of the ocean surface has decreased from approximately 8.25 to 8.14. The root cause of ocean acidification is carbon dioxid ...
, which occurs when the amount of carbon dioxide in the water is increased to unnatural levels. Ocean acidification slows the growth of certain species of fish and shellfish, and even prevents shell formation in certain species of mollusks. These subtle, small changes can add up over time to cause chain reactions and devastating effects on whole marine ecosystems. Other animals that eat exposed shellfish are susceptible to the neurotoxin, which may lead to neurotoxic shellfish poisoning and sometimes even death. Most mollusks and clams filter feed, which results in higher concentrations of the toxin than just drinking the water.Brand et al., Larry E., Lisa Campbell, Eileen Bresnan. "Karenia: The biology and ecology of a toxic genus." Harmful Algae 14 (2012): 156–178. 6 March 2018.
Scaup Scaup is the common name for three species of diving duck: * Greater scaup, or just "scaup", ''Aythya marila'' * Lesser scaup The lesser scaup (''Aythya affinis'') is a small North American diving duck that migrates south as far as Central Ameri ...
, for example, are
diving ducks The diving ducks, commonly called pochards or scaups, are a category of duck which feed by diving beneath the surface of the water. They are part of Anatidae, the diverse and very large Family (biology), family that includes ducks, goose, geese, ...
whose diet mainly consists of mollusks. When scaup eat the filter-feeding shellfish that have accumulated high levels of the HAB toxin, their population becomes a prime target for poisoning. However, even birds that do not eat mollusks can be affected by simply eating dead fish on the beach or drinking the water.Forrester et al., Donald J., Jack M. Gaskin, Franklin H. White. "AN EPIZOOTIC OF WATERFOWL IN FLORIDA." Journal of Wildlife Diseases 13 (1997): 160–167. The toxins released by the blooms can kill marine animals including
dolphin A dolphin is an aquatic mammal within the infraorder Cetacea. Dolphin species belong to the families Delphinidae (the oceanic dolphins), Platanistidae (the Indian river dolphins), Iniidae (the New World river dolphins), Pontoporiidae (the b ...
s, sea turtles, birds, and
manatee Manatees (family Trichechidae, genus ''Trichechus'') are large, fully aquatic, mostly herbivorous marine mammals sometimes known as sea cows. There are three accepted living species of Trichechidae, representing three of the four living speci ...
s. The Florida Manatee, a subspecies of the West Indian Manatee, is a species often impacted by red tide blooms. Florida manatees are often exposed to the poisonous red-tide toxins either by consumption or inhalation. There are many small barnacles, crustaceans, and othe
epiphytes
that grow on the blades of seagrass. These tiny creatures filter particles from the water around them and use these particles as their main food source. During red tide blooms, they also filter the toxic red tide cells from the water, which then becomes concentrated inside them. Although these toxins do not harm epiphytes, they are extremely poisonous to marine creatures who consume (or accidentally consume) the exposed epiphytes, such as manatees. When manatees unknowingly consume exposed epiphytes while grazing on sea grass, the toxins are subsequently released from the epiphytes and ingested by the manatees. In addition to consumption, manatees may also become exposed to air-borne Brevetoxins released from harmful red-tide cells when passing through algal blooms. Manatees also have an immunoresponse to HABs and their toxins that can make them even more susceptible to other stressors. Due to this susceptibility, manatees can die from either the immediate, or the after effects of the HAB. In addition to causing manatee mortalities, red-tide exposure also causes sever
sublethal health problems among Florida manatee populations
Studies have shown that red-tide exposure among free-ranging Florida manatees has been shown to negatively impact immune functioning by causing increased inflammation, a reduction in lymphocyte proliferation responses, and oxidative stress. Fish such as Atlantic herring, American pollock, winter flounder, Atlantic salmon, and cod were dosed orally with these toxins in an experiment, and within minutes the subjects started to exhibit a loss of equilibrium and began to swim in an irregular, jerking pattern, followed by paralysis and shallow, arrhythmic breathing and eventually death, after about an hour.White, A. W. "Sensitivity of Marine Fishes to Toxins from the Red-Tide Dinoflagellate Gonyaulax excavata and Implications for Fish Kills." Marine Biology 65 (1981): 255–260. 6 March 2018. HABs have been shown to have a negative effect also in the memory functions of sea lions.


Potential remedies


Reducing nutrient runoff

Since many algal blooms are caused by a major influx of nutrient-rich runoff into a water body, programs to treat wastewater, reduce the overuse of fertilizers in agriculture and reducing the bulk flow of runoff can be effective for reducing severe algal blooms at river mouths,
estuaries An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environme ...
, and the ocean directly in front of the river's mouth. The nitrates and phosphorus in fertilizers cause algal blooms when they run off into lakes and rivers after heavy rains. Modifications in farming methods have been suggested, such as only using fertilizer in a targeted way at the appropriate time exactly where it can do the most good for crops to reduce potential runoff.Biello, David
"Deadly Algae Are Everywhere, Thanks to Agriculture"
''Scientific American'', August 8, 2014
A method used successfully is
drip irrigation Drip irrigation or trickle irrigation is a type of micro-irrigation system that has the potential to save water and nutrients by allowing water to drip slowly to the roots of plants, either from above the soil surface or buried below the surface. ...
, which instead of widely dispersing fertilizers on fields, drip-irrigates plant roots through a network of tubes and emitters, leaving no traces of fertilizer to be washed away. Drip irrigation also prevents the formation of algal blooms in
reservoirs A reservoir (; from French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store fresh water or it may be a natural formation. Reservoirs can be created in a number of ways, including control ...
for drinking water while saving up to 50% of water typically used by agriculture. There have also been proposals to create buffer zones of foliage and wetlands to help filter out the phosphorus before it reaches water. Other experts have suggested using conservation tillage, changing crop rotations, and restoring wetlands. It is possible for some dead zones to shrink within a year under proper management.Larsen, Janet
"Dead Zones Increasing in the World's Coastal Waters"
Earth Policy Institute, June 16, 2004
There have been a few success stories in controlling chemicals. After Norway's lobster fishery collapsed in 1986 due to low oxygen levels, for instance, the government in neighboring Denmark took action and reduced phosphorus output by 80 percent which brought oxygen levels closer to normal. Similarly, dead zones in the
Black Sea The Black Sea is a marginal mediterranean sea of the Atlantic Ocean lying between Europe and Asia, east of the Balkans, south of the East European Plain, west of the Caucasus, and north of Anatolia. It is bounded by Bulgaria, Georgia, Rom ...
and along the
Danube River The Danube ( ; ) is a river that was once a long-standing frontier of the Roman Empire and today connects 10 European countries, running through their territories or being a border. Originating in Germany, the Danube flows southeast for , pa ...
recovered after phosphorus applications by farmers were reduced by 60%. Nutrients can be permanently removed from wetlands harvesting wetland plants, reducing nutrient influx into surrounding bodies of water. 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. In the U.S., surface runoff is the largest source of nutrients added to rivers and lakes, but is mostly unregulated under the federal
Clean Water Act The Clean Water Act (CWA) is the primary federal law in the United States governing water pollution. Its objective is to restore and maintain the chemical, physical, and biological integrity of the nation's waters; recognizing the responsibiliti ...
. Locally developed initiatives to reduce
nutrient pollution Nutrient pollution, a form of water pollution, refers to contamination by excessive inputs of nutrients. It is a primary cause of eutrophication of surface waters (lakes, rivers and coastal waters), in which excess nutrients, usually nitrogen or ...
are underway in various areas of the country, such as the
Great Lakes The Great Lakes, also called the Great Lakes of North America, are a series of large interconnected freshwater lakes in the mid-east region of North America that connect to the Atlantic Ocean via the Saint Lawrence River. There are five lakes ...
region and the
Chesapeake Bay The Chesapeake Bay ( ) is the largest estuary in the United States. The Bay is located in the Mid-Atlantic region and is primarily separated from the Atlantic Ocean by the Delmarva Peninsula (including the parts: the Eastern Shore of Maryland / ...
. To help reduce algal blooms in
Lake Erie Lake Erie ( "eerie") is the fourth largest lake by surface area of the five Great Lakes in North America and the eleventh-largest globally. It is the southernmost, shallowest, and smallest by volume of the Great Lakes and therefore also ha ...
, the State of
Ohio Ohio () is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. Of the List of states and territories of the United States, fifty U.S. states, it is the List of U.S. states and territories by area, 34th-l ...
presented a plan in 2016 to reduce phosphorus runoff.


Chemical treatment

Although a number of
algaecide Algaecide or algicide is a biocide used for killing and preventing the growth of algae, often defined in a loose sense that, beyond the biological definition, also includes cyanobacteria ("blue-green algae"). An algaecide may be used for controlle ...
s have been effective in killing algae, they have been used mostly in small bodies of water. 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."What is creeping into our lakes?"
''Greensburg Daily News'', August 16, 2016
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. The negative effects can therefore be worse than letting the algae die off naturally."Toxic algal blooms behind Klamath River dams create health risks far downstream"
''Oregon State University News'', June 16, 2015
In 2019,
Chippewa Lake Chippewa Lake (formerly Chippewa-on-the-Lake) is a village in Medina County, Ohio, United States. It is located on Chippewa Lake, a natural inland lake in Ohio. The village was incorporated in 1920. The population was 711 at the 2010 census. ...
in Northeast Ohio became the first lake in the U.S. to successfully test a new chemical treatment. The chemical formula killed all of the toxic algae in the lake within a single day. The formula has already been used in China, South Africa and Israel. In February 2020,
Roodeplaat Dam Roodeplaat Dam is a concrete arch dam situated in South Africa on the Pienaars River (also known along parts of its length as the Moretele River and Moreleta Spruit), a tributary of the Crocodile River, which flows northwards into the Limpopo R ...
in
Gauteng Gauteng ( ) is one of the nine provinces of South Africa. The name in Sotho-Tswana languages means 'place of gold'. Situated on the Highveld, Gauteng is the smallest province by land area in South Africa. Although Gauteng accounts for only ...
Province,
South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring coun ...
was treated with a new algicide formulation against a severe bloom of ''
Microcystis ''Microcystis'' is a genus of freshwater cyanobacteria that includes the harmful algal bloom-forming ''Microcystis aeruginosa''. Many members of a ''Microcystis'' community can produce neurotoxins and hepatotoxins, such as microcystin and cyan ...
'' sp. This formulation allows the granular product to float and slow-release its active ingredient, sodium percarbonate, that releases
hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3 ...
(H2O2), on the water surface. Consequently, the effective concentrations are limited, vertically, to the surface of the water; and spatially to areas where
cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, bl ...
are abundant. This provide the aquatic organisms a “safe haven” in untreated areas and avoids the adverse effects associated with the use of standard algicides. Bioactive compounds isolated from terrestrial and aquatic plants, particularly seaweeds, have seen results as a more environmentally friendly control for HABs. Molecules found in seaweeds such as Corallina,
Sargassum ''Sargassum'' is a genus of brown (class Phaeophyceae) macroalgae ( seaweed) in the order Fucales. Numerous species are distributed throughout the temperate and tropical oceans of the world, where they generally inhabit shallow water and coral ...
, and
Saccharina japonica ''Saccharina japonica'' is a marine species of the Phaeophyceae (brown algae) class, a type of kelp or seaweed, which is extensively cultivated on ropes between the seas of China, Japan and Korea. It has the common name sweet kelp. It is wi ...
have shown to inhibit some bloom-forming microalgae. In addition to their anti-microalgal effects, the bioactive molecules found in these seaweeds also have antibacterial, antifungal, and antioxidant properties.


Removal of HABs using aluminum-modified clay

Other chemicals are being tested for their efficacy for removing cyanobacteria during blooms. Modified clays, such as aluminum chloride modified clay (AC-MC), aluminum sulfide modified clay (AS-MC) and polyaluminum chloride modified clay (PAC-MC) have shown positive results ''in vitro'' for the removal of Aureococcus by trapping the microalgae in the sediment of clay, removing it from the top layer of water where harmful blooms can occur. Many efforts have been made in an attempt to control HAB’s so that the harm that they cause can be kept at a minimum. Studies into the use of clay to control HAB’s have proven that this method may be an effective way to reduce the negative effects caused by HAB’s. The addition of
aluminum chloride Aluminium chloride, also known as aluminium trichloride, is an inorganic compound with the formula . It forms hexahydrate with the formula , containing six water molecules of hydration. Both are colourless crystals, but samples are often contam ...
,
aluminum sulfate Aluminium sulfate is a salt with the formula Al2 (SO4)3. It is soluble in water and is mainly used as a coagulating agent (promoting particle collision by neutralizing charge) in the purification of drinking water and wastewater treatment plan ...
, or polyaluminum chloride to clay can modify the clay surface and increase its efficiency in the removal of HAB’s from a body of water. The addition of aluminum-containing compounds causes the clay particles to achieve a positive charge, with these particles then undergoing
flocculation Flocculation, in the field of chemistry, is a process by which colloidal particles come out of suspension to sediment under the form of floc or flake, either spontaneously or due to the addition of a clarifying agent. The action differs from ...
with the harmful algae cells. The algae cells then group together: becoming a
sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand ...
instead of a suspension. The process of flocculation will limit the bloom growth and reduce the impact in which the bloom can have on an area.


Additional reservoirs

Other experts have proposed building reservoirs to prevent the movement of algae downstream. However, that can lead to the growth of algae within the reservoir, which become sediment traps with a resultant buildup of nutrients. Some researchers found that intensive blooms in reservoirs were the primary source of toxic algae observed downstream, but the movement of algae has so far been less studied, although it is considered a likely cause of algae transport.


Restoring shellfish populations

The decline of filter-feeding shellfish populations, such as
oysters Oyster is the common name for a number of different families of salt-water bivalve molluscs that live in marine or brackish habitats. In some species, the valves are highly calcified, and many are somewhat irregular in shape. Many, but not all ...
, likely contribute to HAB occurrence. As such, numerous research projects are assessing the potential of restored shellfish populations to reduce HAB occurrence.


Improved monitoring

Other remedies include using improved monitoring methods, trying to improve predictability, and testing new potential methods of controlling HABs. 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. Mathematical models are useful to predict future algal blooms.


Sensors and monitoring devices

A growing number of scientists agree that there is an urgent need to protect the public by being able to forecast harmful algal blooms. One way they hope to do that is with sophisticated sensors which can help warn about potential blooms. The same types of sensors can also be used by water treatment facilities to help them prepare for higher toxic levels. The only sensors now in use are located in the Gulf of Mexico. 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. With an increase in the size and frequency of HABs, experts state the need for significantly more sensors located around the country. The same kinds of sensors can also be used to detect threats to drinking water from intentional contamination. Satellite and remote sensing technologies are growing in importance for monitoring, tracking, and detecting HABs. Four U.S. federal agencies—EPA, the
National Aeronautics and Space Administration The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding ...
(NASA), NOAA, and the U.S. Geological Survey (USGS)—are working on ways to detect and measure cyanobacteria blooms using satellite data. The data may help develop early-warning indicators of cyanobacteria blooms by monitoring both local and national coverage."Remote Sensing Provides a National View of Cyanobacteria Blooms"
USGS
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.


Examples


Notable occurrences

* ''
Lingulodinium polyedrum ''Lingulodinium polyedra'' is a species of motile photosynthetic dinoflagellates. ''L. polyedra'' are often the cause of red tides in southern California, leading to bioluminescent displays on beaches at night. Life cycle As part of its life ...
'' produces brilliant displays of bioluminescence in warm coastal waters. Seen in
Southern California Southern California (commonly shortened to SoCal) is a geographic and cultural region that generally comprises the southern portion of the U.S. state of California. It includes the Los Angeles metropolitan area, the second most populous urban ...
regularly since at least 1901. * The largest algal bloom on record was the 1991 Darling River cyanobacterial bloom in Australia, largely of ''
Anabaena circinalis ''Anabaena circinalis'' is a species of Gram-negative, photosynthetic cyanobacteria common to freshwater environments throughout the world. Much of the scientific interest in '' A. circinalis '' owes to its production of several potentially harm ...
'', between October and December 1991 over of the Barwon and
Darling River The Darling River (Paakantyi: ''Baaka'' or ''Barka'') is the third-longest river in Australia, measuring from its source in northern New South Wales to its conflu ence with the Murray River at Wentworth, New South Wales. Including its long ...
s. * 1530: First alleged case off the
Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and ...
Gulf Coast is without foundation. According to Marine Lab at University of Miami, the first possible Red Tide in Florida was in 1844. Earlier "signs" were from boats sorting fish on their way to home port dumping trash fish overboard. Thus "dead fish" reports along the coast were not Red Tide. * 1793: The first recorded case occurring in
British Columbia British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, for ...
,
Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by to ...
. * 1840: No deaths of humans have been attributed to Florida red tide, but people may experience respiratory irritation (coughing, sneezing, and tearing) when the red tide organism (''Karenia brevis'') is present along a coast and winds blow its aerosolized toxins. Swimming is usually safe, but skin irritation and burning is possible in areas of high concentration of red tide. *1844: First possible case off the Florida Gulf Coast according to Marine Lab University of Miami, probably by ships off shore, no known inhabitants of the coast reporting. *1916: Massive fish kill along SW Florida coast. Noxious air thought to be seismic underwater explosion releasing chlorine gas. *1947: Southwest Florida: A massive bloom that lasts close a year almost destroys the commercial fishing industry and sponge beds. The resulting poisoned surf caused beaches to need to be evacuated. * 1972: A red tide was caused in New England by a toxic dinoflagellate ''Alexandrium (Gonyaulax) tamarense''. The red tides caused by the dinoflagellate '' Gonyaulax'' are serious because this organism produces saxitoxin and gonyautoxins which accumulate in shellfish and if ingested may lead to paralytic shellfish poisoning (PSP) and can lead to death. * 1972 and 1973: Red tides killed two villagers west of Port Moresby. In March 1973 a red tide invaded Port Moresby Harbour and destroyed a Japanese pearl farm. * In 1972, a red tide was caused in
New England New England is a region comprising six states in the Northeastern United States: Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont. It is bordered by the state of New York to the west and by the Canadian provinces ...
by a toxic dinoflagellate '' Alexandrium (Gonyaulax) tamarense''. * 1976: The first PSP case in
Sabah Sabah () is a state of Malaysia located in northern Borneo, in the region of East Malaysia. Sabah borders the Malaysian state of Sarawak to the southwest and the North Kalimantan province of Indonesia to the south. The Federal Territory ...
,
Malaysian Borneo East Malaysia (), or the Borneo States, also known as Malaysian Borneo, is the part of Malaysia on and near the island of Borneo, the world's third-largest island. Near the coast of Sabah is a small archipelago called Labuan. East Malaysia li ...
where 202 victims were reported to be suffering and 7 deaths. * 1987: A red algae bloom in
Prince Edward Island Prince Edward Island (PEI; ) is one of the thirteen provinces and territories of Canada. It is the smallest province in terms of land area and population, but the most densely populated. The island has several nicknames: "Garden of the Gulf", ...
caused over a million dollars in losses. * 2005: The Canadian red tide was discovered to have come further south than it has in years prior by the ship (R/V) Oceanus, closing shellfish beds in Maine and Massachusetts and alerting authorities as far south as Montauk (
Long Island Long Island is a densely populated island in the southeastern region of the U.S. state of New York, part of the New York metropolitan area. With over 8 million people, Long Island is the most populous island in the United States and the 18 ...
, NY) to check their beds. Experts who discovered the reproductive cysts in the seabed warn of a possible spread to Long Island in the future, halting the area's fishing and shellfish industry and threatening the tourist trade, which constitutes a significant portion of the island's economy. * In 2008 large blooms of the algae ''Cochlodinium polykrikoid'' were found along the Chesapeake Bay and nearby tributaries such as the James River, causing millions of dollars in damage and numerous beach closures. * In 2009, Brittany, France experienced recurring macroalgal blooms caused by the high amount of fertilizer discharging in the sea due to intensive pig farming, causing lethal gas emissions that have led to one case of human unconsciousness and three animal deaths. * In 2010, dissolved iron in the ash from the Eyjafjallajökull volcano triggered a plankton bloom in the
North Atlantic The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe a ...
. * 2011: Northern California * 2011:
Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of the United ...
* In 2013, an algal bloom was caused in
Qingdao Qingdao (, also spelled Tsingtao; , Mandarin: ) is a major city in eastern Shandong Province. The city's name in Chinese characters literally means " azure island". Located on China's Yellow Sea coast, it is a major nodal city of the One Belt ...
,
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...
, by
sea lettuce The sea lettuces comprise the genus ''Ulva'', a group of edible green algae that is widely distributed along the coasts of the world's oceans. The type species within the genus ''Ulva'' is ''Ulva lactuca'', wikt:lactuca, ''lactuca'' being Latin ...
. * 2013: In January, a red tide occurred again on the West Coast
Sea The sea, connected as the world ocean or simply the ocean, is the body of salty water that covers approximately 71% of the Earth's surface. The word sea is also used to denote second-order sections of the sea, such as the Mediterranean Sea, ...
of
Sabah Sabah () is a state of Malaysia located in northern Borneo, in the region of East Malaysia. Sabah borders the Malaysian state of Sarawak to the southwest and the North Kalimantan province of Indonesia to the south. The Federal Territory ...
in the
Malaysian Borneo East Malaysia (), or the Borneo States, also known as Malaysian Borneo, is the part of Malaysia on and near the island of Borneo, the world's third-largest island. Near the coast of Sabah is a small archipelago called Labuan. East Malaysia li ...
. Two human fatalities were reported after they consumed
shellfish Shellfish is a colloquial and fisheries term for exoskeleton-bearing aquatic invertebrates used as food, including various species of molluscs, crustaceans, and echinoderms. Although most kinds of shellfish are harvested from saltwater environ ...
contaminated with the red tide toxin. * 2013: In January, a red tide bloom appeared at Sarasota beach – mainly Siesta Key, Florida causing a fish kill that had a negative impact on tourists, and caused respiratory issues for beach-goers. * In 2014, ''
Myrionecta rubra ''Mesodinium rubrum'' (or ''Myrionecta rubra'') is a species of ciliates. It constitutes a plankton community and is found throughout the year, most abundantly in spring and fall, in coastal areas. Although discovered in 1908, its scientific i ...
'' (previously known as ''Mesodinium rubrum''), a
ciliate The ciliates are a group of alveolates characterized by the presence of hair-like organelles called cilia, which are identical in structure to eukaryotic flagella, but are in general shorter and present in much larger numbers, with a differen ...
protist that ingests cryptomonad algae, caused a bloom in southeastern coast of
Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...
. * In 2014, blue green algae caused a bloom in the western basin of
Lake Erie Lake Erie ( "eerie") is the fourth largest lake by surface area of the five Great Lakes in North America and the eleventh-largest globally. It is the southernmost, shallowest, and smallest by volume of the Great Lakes and therefore also ha ...
, poisoning the
Toledo, Ohio Toledo ( ) is a city in and the county seat of Lucas County, Ohio, United States. A major Midwestern United States port city, Toledo is the fourth-most populous city in the state of Ohio, after Columbus, Ohio, Columbus, Cleveland, and Cincinnat ...
water system connected to 500,000 people. * 2014: In August, massive 'Florida red tide' long and wide. * 2015: June, 12 persons hospitalized in the Philippine province of
Bohol Bohol (), officially the Province of Bohol ( ceb, Lalawigan sa Bohol; tl, Lalawigan ng Bohol), is an island province of the Philippines located in the Central Visayas region, consisting of the island itself and 75 minor surrounding islands. ...
for red tide poisoning. * 2015: August, several beaches in the Netherlands between
Katwijk Katwijk (), also spelled Katwyk, is a coastal municipality and town in the province of South Holland, which is situated in the mid-western part of the Netherlands. The Oude Rijn ("Old Rhine") river flows through the town and into the North Se ...
and
Scheveningen Scheveningen is one of the eight districts of The Hague, Netherlands, as well as a subdistrict (''wijk'') of that city. Scheveningen is a modern seaside resort with a long, sandy beach, an esplanade, a pier, and a lighthouse. The beach is ...
were plagued. Government institutions dissuaded swimmers from entering the water. * 2015: September, a red tide bloom occurred in the Gulf of Mexico, affecting
Padre Island National Seashore Padre Island National Seashore (PINS) is a national seashore located on Padre Island off the coast of South Texas. In contrast to South Padre Island, known for its beaches and vacationing college students, PINS is located on North Padre Isla ...
along
North Padre Island North Padre Island is a barrier island along the coast of Texas. It and South Padre Island were formed after the creation of the Port Mansfield Channel split Padre Island in two. From north to south, North Padre Island is located in parts of Nu ...
and
South Padre Island South Padre Island is a barrier island in the U.S. state of Texas. The remote landform is located in Cameron County, Willacy County, and accessible by the Queen Isabella Causeway. South Padre Island was formed when the creation of the Port Man ...
in Texas. * 2017 and 2018: ''K. brevis'' red tide algae with warnings not to swim, state of emergency declared, dead
dolphin A dolphin is an aquatic mammal within the infraorder Cetacea. Dolphin species belong to the families Delphinidae (the oceanic dolphins), Platanistidae (the Indian river dolphins), Iniidae (the New World river dolphins), Pontoporiidae (the b ...
and
manatee Manatees (family Trichechidae, genus ''Trichechus'') are large, fully aquatic, mostly herbivorous marine mammals sometimes known as sea cows. There are three accepted living species of Trichechidae, representing three of the four living speci ...
, worsened by Caloosahatchee River. Peaked in the summer of 2018. Toxic harmful algae bloom red tide in Southwest Florida. A rare harmful algal bloom along Florida's east coast of
Palm Beach County Palm Beach County is a county located in the southeastern part of Florida and lies directly north of Broward County and Miami-Dade County. The county had a population of 1,492,191 as of the 2020 census, making it the third-most populous county ...
occurred the weekend of September 30, 2018. * In 2019, blue-green algae, or
Cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, bl ...
blooms, were again problematic on Lake Erie. In early August 2019, satellite images depicted a bloom stretching up to 1,300 square kilometers, with the epicentre near
Toledo, Ohio Toledo ( ) is a city in and the county seat of Lucas County, Ohio, United States. A major Midwestern United States port city, Toledo is the fourth-most populous city in the state of Ohio, after Columbus, Ohio, Columbus, Cleveland, and Cincinnat ...
. The largest Lake Erie bloom to date occurred in 2015, exceeding the severity index at 10.5 and in 2011 at a 10. A large bloom does not necessarily mean the cyanobacteria ... will produce toxins", said Michael McKay, of the
University of Windsor , mottoeng = Goodness, Discipline and Knowledge , established = , academic_affiliations = CARL, COU, Universities Canada , former_names = Assumption College (1857-1956)Assumption University of Windsor (1956-1963) , type = Public universi ...
. Water quality testing was underway in August. * In 2019, a bloom of ''Noctiluca'' algae caused bioluminescent glow off the coast of Chennai, India. Similar blooms have been reported annually in the northern
Arabian Sea The Arabian Sea ( ar, اَلْبَحرْ ٱلْعَرَبِيُّ, Al-Bahr al-ˁArabī) is a region of the northern Indian Ocean bounded on the north by Pakistan, Iran and the Gulf of Oman, on the west by the Gulf of Aden, Guardafui Channe ...
since the early 2000s. *2021: In July, a large red tide occurred on the
Gulf Coast The Gulf Coast of the United States, also known as the Gulf South, is the coast, coastline along the Southern United States where they meet the Gulf of Mexico. The list of U.S. states and territories by coastline, coastal states that have a shor ...
of Florida in and around
Tampa Bay Tampa Bay is a large natural harbor and shallow estuary connected to the Gulf of Mexico on the west-central coast of Florida, comprising Hillsborough Bay, McKay Bay, Old Tampa Bay, Middle Tampa Bay, and Lower Tampa Bay. The largest freshwater ...
. The event has caused the death of millions of pounds of fish, and led to the National Weather Service declaring a Beach Hazard. *2021: in October, the 2021 North-East England shellfish die-off, mass deaths of shellfish (specifically crabs and lobster) on the beaches of Northern England, led to and algal bloom being blamed as the cause by the UK Government. However, those who work in the fishing industry in the area, and some academics, have stated that pyridine poisoning is the cause.


United States

In July 2016
Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and ...
declared a state of emergency for four counties as a result of blooms. They were said to be "destroying" a number of businesses and affecting local economies, with many needing to shut down entirely. Some beaches were closed, and hotels and restaurants suffered a drop in business. Tourist sporting activities such as fishing and boating were also affected."Toxic algae driving away Florida beachgoers"
''CNBC'', July 5, 2016
In 2019, the biggest
Sargassum ''Sargassum'' is a genus of brown (class Phaeophyceae) macroalgae ( seaweed) in the order Fucales. Numerous species are distributed throughout the temperate and tropical oceans of the world, where they generally inhabit shallow water and coral ...
bloom ever seen created a crisis in the Tourism industry in North America. This event was likely caused by climate change and
nutrient pollution Nutrient pollution, a form of water pollution, refers to contamination by excessive inputs of nutrients. It is a primary cause of eutrophication of surface waters (lakes, rivers and coastal waters), in which excess nutrients, usually nitrogen or ...
from fertilizers. 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.


On the U.S. coasts

The Gulf of Maine frequently experiences blooms of the
dinoflagellate The dinoflagellates ( Greek δῖνος ''dinos'' "whirling" and Latin ''flagellum'' "whip, scourge") are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered algae. Dinoflagellates are ...
''Alexandrium fundyense'', an organism that produces
saxitoxin Saxitoxin (STX) is a potent neurotoxin and the best-known paralytic shellfish toxin (PST). Ingestion of saxitoxin by humans, usually by consumption of shellfish contaminated by toxic algal blooms, is responsible for the illness known as paralyti ...
, the neurotoxin responsible for
paralytic shellfish poisoning Paralytic shellfish poisoning (PSP) is one of the four recognized syndromes of shellfish poisoning, which share some common features and are primarily associated with bivalve mollusks (such as mussels, clams, oysters and scallops). These shellfi ...
. The well-known "Florida red tide" that occurs in the Gulf of Mexico is a HAB caused by ''
Karenia brevis ''Karenia brevis'' is a microscopic, single-celled, photosynthetic organism in the genus '' Karenia''. It is a marine dinoflagellate commonly found in the waters of the Gulf of Mexico. It is the organism responsible for the "Florida red tides" ...
'', another dinoflagellate which produces brevetoxin, the neurotoxin responsible for neurotoxic shellfish poisoning. California coastal waters also experience seasonal blooms of ''
Pseudo-nitzschia ''Pseudo-nitzschia'' is a marine planktonic diatom genus that accounts for 4.4% of pennate diatoms found worldwide. Some species are capable of producing the neurotoxin domoic acid (DA), which is responsible for the neurological disorder in huma ...
'', a
diatom A diatom ( Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising se ...
known to produce
domoic acid Domoic acid (DA) is a kainic acid-type neurotoxin that causes amnesic shellfish poisoning (ASP). It is produced by algae and accumulates in shellfish, sardines, and anchovies. When sea lions, otters, cetaceans, humans, and other predators eat c ...
, the neurotoxin responsible for
amnesic shellfish poisoning Amnesic shellfish poisoning (ASP) is an illness caused by consumption of shellfish that contain the marine biotoxin called domoic acid. In mammals, including humans, domoic acid acts as a neurotoxin, causing permanent short-term memory loss, bra ...
. The term red tide is most often used in the US to refer to ''
Karenia brevis ''Karenia brevis'' is a microscopic, single-celled, photosynthetic organism in the genus '' Karenia''. It is a marine dinoflagellate commonly found in the waters of the Gulf of Mexico. It is the organism responsible for the "Florida red tides" ...
'' blooms in the eastern
Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of the United ...
, also called the Florida red tide. ''K. brevis'' is one of many different species of the genus ''Karenia'' found in the world's oceans. Major advances have occurred in the study of dinoflagellates and their genomics. Some include identification of the toxin-producing genes (Polyketide synthase, ''PKS'' genes), exploration of environmental changes (temperature, light/dark, etc.) have on gene expression, as well as an appreciation of the complexity of the ''Karenia'' genome. These blooms have been documented since the 1800s, and occur almost annually along Florida's coasts. There was increased research activity of harmful algae blooms (HABs) in the 1980s and 1990s. This was primarily driven by media attention from the discovery of new HAB organisms and the potential adverse health effects of their exposure to animals and humans. The Florida red tides have been observed to have spread as far as the eastern coast of Mexico. The density of these organisms during a bloom can exceed tens of millions of cells per litre of seawater, and often discolor the water a deep reddish-brown hue. Red tide is also sometimes used to describe harmful algal blooms on the northeast coast of the United States, particularly in the Gulf of Maine. This type of bloom is caused by another species of dinoflagellate known as ''Alexandrium fundyense''. These blooms of organisms cause severe disruptions in fishery, fisheries of these waters, as the toxins in these organism cause filter-feeding shellfish in affected waters to become poisonous for human consumption due to saxitoxin. The related ''Alexandrium monilatum'' is found in subtropical or tropical shallow seas and
estuaries An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environme ...
in the western Atlantic Ocean, the Caribbean Sea, the Gulf of Mexico, and the eastern
Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the conti ...
.


Texas

Natural water reservoirs in Texas have been threatened by anthropogenic activities due to large petroleum refineries and oil wells (i.e. emission and wastewater discharge), massive agricultural activities (i.e. pesticide release) and mining extractions (i.e. toxic wastewater) as well as natural phenomena involving frequent HAB events. For the first time in 1985, the state of Texas documented the presence of the ''P. parvum'' (golden alga) bloom along the Pecos River. This phenomenon has affected 33 reservoirs in Texas along major river systems, including the Brazos, Canadian, Rio Grande, Colorado, and Red River, and has resulted in the death of more than 27 million fish and caused tens of millions of dollars in damage.


Chesapeake Bay

The
Chesapeake Bay The Chesapeake Bay ( ) is the largest estuary in the United States. The Bay is located in the Mid-Atlantic region and is primarily separated from the Atlantic Ocean by the Delmarva Peninsula (including the parts: the Eastern Shore of Maryland / ...
, the largest estuary in the U.S., has suffered from repeated large algal blooms for decades due to chemical runoff from multiple sources, including 9 large rivers and 141 smaller streams and creeks in parts of six states. In addition, the water is quite shallow and only 1% of the waste entering it gets flushed into the ocean. By weight, 60% of the phosphates entering the bay in 2003 were from sewage treatment plants, while 60% of its nitrates came from fertilizer runoff, farm animal waste, and the atmosphere. About 300 million pounds (140 Gg) of nitrates are added to the bay each year. The population increase in the bay drainage basin, watershed, from 3.7 million people in 1940 to 18 million in 2015 is also a major factor, as economic growth leads to the increased use of fertilizers and rising emissions of industrial waste. As of 2015, the six states and the local governments in the Chesapeake watershed have upgraded their sewage treatment plants to control nutrient discharges. The U.S. Environmental Protection Agency (EPA) estimates that sewage treatment plant improvements in the Chesapeake region between 1985 and 2015 have prevented the discharge of 900 million pounds (410 Gg) of nutrients, with nitrogen discharges reduced by 57% and phosphorus by 75%. Agricultural and urban runoff pollution continue to be major sources of nutrients in the bay, and efforts to manage those problems are continuing throughout the watershed.


Lake Erie

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. The International Joint Commission has called on United States and Canada to drastically reduce phosphorus loads into Lake Erie to address the threat.


Green Bay

Green Bay has a dead zone caused by phosphorus pollution that appears to be getting worse.


Okeechobee Waterway

Lake Okeechobee is an ideal habitat for cyanobacteria because its shallow, sunny, and laden with nutrients from Florida's agriculture. The Okeechobee Waterway connects the lake to the Atlantic Ocean and the
Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of the United ...
through the St. Lucie River and the Caloosahatchee River, Caloosahatchee respectively. This means that harmful algal blooms are carried down the estuaries as water is released during the wet summer months. In July 2018 up to 90% of Lake Okeechobee was covered in algae. Water draining from the lake filled the region with a noxious odor and caused respiratory problems in some humans during the following month. To make matters worse, harmful red tide blooms are historically common on Florida's coasts during these same summer months. Cyanobacteria in the rivers die as they reach saltwater but their nitrogen fixation feeds the red tide on the coast. Areas at the mouth of the estuaries such as Cape Coral, Florida, Cape Coral and Port St. Lucie, Florida, Port St. Lucie therefore experience the compounded effects of both types of harmful algal bloom. Cleanup crews hired by authorities in Lee County, Florida, Lee County - where the Caloosahatchee meets the Gulf of Mexico - removed more than 1700 tons of dead marine life in August 2018.


Baltic Sea

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. This is seen by the Baltic Sea Action Group as a threat to biodiversity and regional fishing stocks.


Coastal seas of Bangladesh, India, and Pakistan

Open defecation is common in south Asia, but human waste is an often overlooked source of nutrient pollution in marine pollution modeling. When nitrogen (N) and phosphorus (P) contributed by human waste was included in models for Bangladesh, India, and Pakistan, the estimated N and P inputs to bodies of water increased one to two orders of magnitude compared to previous models. River export of nutrients to coastal seas increases coastal
eutrophication Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phyt ...
potential (ICEP). The ICEP of the Godavari River is three times higher when N and P inputs from human waste are included.


See also

* Brevetoxin * Ciguatera * Cyanobacterial bloom * Cyanotoxin * GEOHAB - an international research programme on the Global Ecology and Oceanography of Harmful algal blooms * Milky seas effect – A phenomenon in which disturbed red algae dinoflagellates will make the water glow blue, at night * ''Pfiesteria'' *Thin layers (oceanography) *Water quality *Water security


References

{{Reflist, colwidth=30em


External links


International Society for the Study of Harmful Algae (ISSHA)FAQ about Harmful Algal Blooms
(NOAA)
Harmful Algal Blooms Observing System
(NOAA/HAB-OFS)
GEOHAB: The International IOC-SCOR Research Programme on the Global Ecology and Oceanography of Harmful Algal Blooms
Biological oceanography Aquatic ecology Fishing industry Water quality indicators Human impact on the environment Agriculture and the environment Climate change and the environment Water pollution Algal blooms Red tide Dinoflagellate biology Fisheries science