GetWiki

{{Short description|Population explosion of organisms that can kill marine life}}{{Redirect|Red tide|the athletic programs of the University of Alabama|Alabama Crimson Tide}}File:Blue-gree algae bloom Lake Erie.png|thumb|Cyanobacteria (blue-green algae) bloom on Lake ErieLake ErieA harmful algal bloom (HAB), or excessive algae growth, is an algal bloom 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 or fresh waters.JOURNAL, Eutrophication and harmful algal blooms: A scientific consensus, J. Heisler, P.M. Glibert, J.M. Burkholder, D.M. Anderson, W. Cochlan, W.C. Dennison b, Q. Dortch, C.J. Gobler, C.A. Heil, E. Humphries, A. Lewitus, R. Magnien, H.G. Marshallm, K. Sellner, D.A. Stockwell, D.K. Stoecker, M. Suddleson, Harmful Algae, 8, 1, 2008, 3–13, 10.1016/j.hal.2008.08.006, 28781587, 5543702, 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".JOURNAL, Anderson, Donald M., Glibert, Patricia M., Patricia Glibert, Burkholder, Joann M., JoAnn Burkholder, Harmful algal blooms and eutrophication: Nutrient sources, composition, and consequences, Estuaries, August 2002, 25, 4, 704–726, 10.1007/BF02804901, 44207554,weblink 7 April 2021, WEB, Hall, Danielle, What Exactly Is a Red Tide?,weblink Smithsonian, 7 April 2021, 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, which is an overabundance of nutrients in the water. The two most common nutrients are fixed nitrogen (nitrates, ammonia, and urea) and phosphate.WEB,weblink Harmful Algal Blooms, 9 March 2021, Centers for Disease Control and Prevention, CDC, The excess nutrients are emitted by agriculture, industrial pollution, excessive fertilizer use in urban/suburban areas, and associated urban runoff. Higher water temperature and low circulation also contribute.{{citation needed|date=August 2023}}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. The U.S. National Oceanic and Atmospheric Administration (NOAA) predicts more harmful blooms in the Pacific Ocean.NEWS, Harvey, Chelsea, 2016-09-29, The Pacific blob caused an "unprecedented" toxic algal bloom — and there's more to come,weblink Washington Post, Potential remedies include chemical treatment, additional reservoirs, sensors and monitoring devices, reducing nutrient runoff, research and management as well as monitoring and reporting.{{citation needed|date=August 2023}}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 of nutrients from the sea floor, 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 and their biological effects.{{TOC limit|3}}{{Plankton sidebar|bloom}}

Description and identification

File:Banter See 1348.jpg|thumb|CyanobacteriaCyanobacteriaHABs from cyanobacteria (blue-green algae) can appear as a foam, scum, or mat on or just below the surface of water and can take on various colors depending on their pigments. Cyanobacteria blooms in freshwater lakes or rivers may appear bright green, often with surface streaks that look like floating paint. Cyanobacterial blooms are a global problem.JOURNAL, Harke, Matthew J., Steffen, Morgan M., Gobler, Christopher J., Otten, Timothy G., Wilhelm, Steven W., Wood, Susanna A., Paerl, Hans W., 2016-04-01, A review of the global ecology, genomics, and biogeography of the toxic cyanobacterium, Microcystis spp., Harmful Algae, Global Expansion of Harmful Cyanobacterial Blooms: Diversity, ecology, causes, and controls, en, 54, 4–20, 10.1016/j.hal.2015.12.007, 28073480, 1568-9883, free, Most blooms occur in warm waters with excessive nutrients. The harmful effects from such blooms are 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 blooms 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.JOURNAL, Rinta-Kanto, J. M., Ouellette, A. J. A., Boyer, G. L., Twiss, M. R., Bridgeman, T. B., Wilhelm, S. W., June 2005, Quantification of Toxic Microcystis spp. during the 2003 and 2004 Blooms in Western Lake Erie using Quantitative Real-Time PCR,weblink Environmental Science & Technology, en, 39, 11, 4198–4205, 10.1021/es048249u, 15984800, 2005EnST...39.4198R, 0013-936X,

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".JOURNAL, Kudela, Raphael, Berdalet, Elisa, Enevoldsen, Henrik, Pitcher, Grant, Raine, Robin, Urban, Ed, GEOHAB–The Global Ecology and Oceanography of Harmful Algal Blooms Program: Motivation, Goals, and Legacy, Oceanography, 1 March 2017, 30, 1, 12–21, 10.5670/oceanog.2017.106, free, 10261/151090, free, 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 in 2008 who stated that HABs include "potentially toxic (auxotrophic, heterotrophic) species and high-biomass producers that can cause hypoxia and anoxia and indiscriminate 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, such as Karenia brevis.WEB, Harmful Algal Blooms (HABs): Red Tide,weblink 2 Oct 2011, U.S. Centers for Disease Control and Prevention, However, the term is misleading since algal blooms can widely vary in color, and growth of algae is unrelated to the tides. Not all red tides are produced by dinoflagellates. The mixotrophic ciliate Mesodinium rubrum produces non-toxic blooms coloured deep red by chloroplasts it obtains from the algae it eats.{{hsp}}JOURNAL, Dierssen, Heidi, McManus, George B., Chlus, Adam, Qiu, Dajun, Gao, Bo-Cai, Lin, Senjie, 2015, Space station image captures a red tide ciliate bloom at high spectral and spatial resolution, Proceedings of the National Academy of Sciences, 112, 48, 14783–14787, 2015PNAS..11214783D, 10.1073/pnas.1512538112, 4672822, 26627232, free, File:Karenia brevis Anatomy (1).png|thumb|The dinoflagellate labeled above is the microscopic alga Karenia brevis. It is the cause of a HAB event in the Gulf of Mexico. The algae propel themselves using a longitudinal flagellum (A) and a transverse flagellum (B). The longitudinal flagellum lies in a groove-like structure called the cingulum (F). The dinoflagellatedinoflagellateAs 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" for benign species.{{citation needed|date=January 2023}}

Types

There are three main types of phytoplankton which can form into harmful algal blooms: cyanobacteria, dinoflagellates and diatoms. All three are made up of microscopic floating organisms which, like plants, can create their own food from sunlight by means of photosynthesis. That ability makes the majority of them an essential part of the food web for small fish and other organisms.Black, Jacquelyn G., and Black, Laura J. Microbiology: Principles and Explorations, 8th Ed., John Wiley & Sons (2012){{rp|246}}

Cyanobacteria

Harmful algal blooms in freshwater lakes and rivers, or at estuaries, 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,JOURNAL, Stanier, R Y, Bazine, G C, October 1977, Phototrophic Prokaryotes: The Cyanobacteria, Annual Review of Microbiology, 31, 1, 225–274, 10.1146/annurev.mi.31.100177.001301, 410354, 0066-4227, as opposed to algae which are eukaryotes.JOURNAL, Yoon, Hwan Su, Hackett, Jeremiah D., Ciniglia, Claudia, Pinto, Gabriele, Bhattacharya, Debashish, 2004, A Molecular Timeline for the Origin of Photosynthetic Eukaryotes, Molecular Biology and Evolution, 21, 5, 809–818, 10.1093/molbev/msh075, 14963099, 1537-1719, free, 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 hepatotoxins, as well as neurotoxins, cytotoxins, and endotoxins.JOURNAL, Bláha, Luděk, Babica, Pavel, Maršálek, Blahoslav, 2009-01-01, Toxins produced in cyanobacterial water blooms – toxicity and risks, Interdisciplinary Toxicology, 2, 2, 36–41, 10.2478/v10102-009-0006-2, 21217843, 1337-9569, 2984099, Water purification 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.WEB, 2021-08-30, Summer Days Are Waning But Algal Blooms Are Growing,weblink 2021-09-22, WAMC, en, WEB, ArcGIS Web Application,weblink 2021-09-22, nysdec.maps.arcgis.com, In September 2021, Spokane County's Environmental Programs issued a HAB alert for Newman Lake following tests showing potentially harmful toxicity levels for cyanobacteria,WEB, Harmful Algae Alert for Newman Lake,weblink 2021-09-22, SRHD, en-US, 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.WEB, Walton, Brett, 2021-09-22, Toxin Levels Spike, Prompting Drinking Water Emergency in Northern California,weblink 2021-09-22, Circle of Blue, en-US, Water conditions in Florida, meanwhile, continue to deteriorate under increasing nutrient inflows, causing severe HAB events in both freshwater and marine areas.WEB, 2021-09-20, Red tide and algae blooms: Florida waters in crisis,weblink 2021-09-22, WFTS, en, 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.WEB,weblink 'Dead zone' is a more common term for hypoxia, which refers to a reduced level of oxygen in the water, Administration, US Department of Commerce, National Oceanic and Atmospheric, oceanservice.noaa.gov, EN-US, 2017-10-22,

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 resting stage and a pelagic 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, haloclines, and pycnoclines that are associated with the bodies of water in which these cells exist.JOURNAL, Tobin, Elizabeth D., Grünbaum, Daniel, Patterson, Johnathan, Cattolico, Rose Ann, 2013-10-04, Behavioral and Physiological Changes during Benthic-Pelagic Transition in the Harmful Alga, Heterosigma akashiwo: Potential for Rapid Bloom Formation, PLOS ONE, en, 8, 10, e76663, 2013PLoSO...876663T, 10.1371/journal.pone.0076663, 1932-6203, 3790758, 24124586, free,

Diatoms and dinoflagellates (in marine coastal areas)

File:La-Jolla-Red-Tide.780.jpg|thumb|A harmful algal bloom event off the coast of San Diego, CaliforniaSan Diego, CaliforniaThe other types of algae are diatoms and dinoflagellates, 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 DepartmentJOURNAL, 2013-08-01, Red tides of the dinoflagellate Noctiluca scintillans associated with eutrophication in the Sea of Marmara (the Dardanelles, Turkey), Oceanologia, en, 55, 3, 709–732, 10.5697/oc.55-3.709, 0078-3234, free, 2013Ocga...55..709T, Turkoglu, Muhammet, although in many instances, particularly when they form close to coastlines or in estuaries, it has been shown that they are exacerbated by human-induced eutrophication and/or climate change.JOURNAL, Chen, Xiu-hua, Zhu, Liang-sheng, Zhang, Hong-sheng, 2007, Numerical Simulation of Summer Circulation in the East China Sea and Its Application in Estimating the Sources of Red Tides in the Yangtze River Estuary and Adjacent Sea Areas, Journal of Hydrodynamics, 19, 3, 272–281, 10.1016/s1001-6058(07)60059-6, 2007JHyDy..19..272C, 119393454, 1001-6058, JOURNAL, Velikova, Violeta, Moncheva, Snejana, Petrova, Daniela, 1999, Phytoplankton dynamics and Red Tides (1987-1997) in the Bulgarian Black Sea, Water Science and Technology, 39, 8, 27–36, 10.2166/wst.1999.0378, 0273-1223, JOURNAL, Song, Yantao, Wang, Ping, Li, Guangdi, Zhou, Daowei, 2014, Relationships between functional diversity and ecosystem functioning: A review, Acta Ecologica Sinica, 34, 2, 85–91, 10.1016/j.chnaes.2014.01.001, 2014AcEcS..34...85S, 1872-2032, JOURNAL, Phlips, Edward J., Badylak, Susan, Lasi, Margaret A., Chamberlain, Robert, Green, Whitney C., Hall, Lauren M., Hart, Jane A., Lockwood, Jean C., Miller, Janice D., Morris, Lori J., Steward, Joel S., 2015, From Red Tides to Green and Brown Tides: Bloom Dynamics in a Restricted Subtropical Lagoon Under Shifting Climatic Conditions, Estuaries and Coasts, en, 38, 3, 886–904, 10.1007/s12237-014-9874-6, 2015EstCo..38..886P, 83480080, 1559-2731, 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" {{Webarchive|url=https://web.archive.org/web/20160804000641weblink |date=2016-08-04 }}, 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."Intense, widespread algal blooms reported in Chesapeake Bay", Science Daily, Sept. 1, 2015Diatoms produce domoic acid, 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, sardines, and anchovies, which if then eaten by sea lions, otters, cetaceans, birds or people, can affect the nervous system causing serious injury or death. In the summer of 2015, the state governments closed important shellfish fisheries in Washington, Oregon and California 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 2015In 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 or microalgae, 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.JOURNAL, Landsberg, J. H., 2002, The effects of harmful algal blooms on aquatic organisms, Reviews in Fisheries Science, 10, 2, 113–390, 10.1080/20026491051695, 2002RvFS...10..113L, 86185142, 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.{{citation needed|date=January 2023}}

List of common HAB genera

{{div col}}

• Gonyaulax
• Karenia
• Gymnodinium
• Dinophysis
• Noctiluca
• Chattonella
• Ceratium
• Amoebophyre
• Alexandrium
• Cochlodinium

{{div col end}}

Causes

(File:Nonvisible cyanobacteria HAB.png|thumb|300px| Harmful algal blooms do not have to be clearly visible. This shows a bloom with high cyanobacteria toxin levels (over 5 μ/l) yet the bloom is not easy to see.Harmful Algal Blooms and Hypoxia in the Great Lakes Research Plan and Action Strategy: An Interagency Report National Science and Technology Council, August 2017, page 21.)It is sometimes unclear what causes specific HABs as their occurrence in some locations appears to be entirely natural,JOURNAL, Adams, N. G., Lesoing, M., Trainer, V. L., 2000, Environmental conditions associated with domoic acid in razor clams on the Washington coast, J Shellfish Res, 19, 1007–1015, while in others they appear to be a result of human activities.BOOK, Lam, C. W. Y., Red tides. biology, environmental science and toxicology, Ho, K. C., Elsevier, 1989, 978-0-444-01343-9, Okaichi, T., New York, 49–52, Red tides in Tolo Harbor, Hong Kong, Anderson, D. M., Nemoto, T., 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.JOURNAL, Trainer, V. L., Adams, N. G., Bill, B. D., Stehr, C. M., Wekell, J. C., Moeller, P., Busman, M., Woodruff, D., 2000, Domoic acid production near California coastal upwelling zones, June 1998, Limnol Oceanogr, 45, 8, 1818–1833, 2000LimOc..45.1818T, 10.4319/lo.2000.45.8.1818, free, 54007265, 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, urea, 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 produced by humans (including iron fertilization) and systematic increase in sea water temperature have also been suggested as possible contributing factors in HABs.JOURNAL, Moore, S., etal, 2011, Impacts of climate variability and future climate change on harmful algal blooms and human health, Proceedings of the Centers for Oceans and Human Health Investigators Meeting, 7, Suppl 2, S4, 10.1186/1476-069X-7-S2-S4, 2586717, 19025675, free, Among the causes of algal blooms are:JOURNAL, Janssen, Annette BG, Janse, Jan H, Beusen, Arthur HW, Chang, Manqi, Harrison, John A, Huttunen, Inese, Kong, Xiangzhen, Rost, Jasmijn, Teurlincx, Sven, Troost, Tineke A, van Wijk, Dianneke, 2019, How to model algal blooms in any lake on earth, Current Opinion in Environmental Sustainability, Elsevier, 36, 1–10, 10.1016/j.cosust.2018.09.001, 1877-3435, Mooij, Wolf M, 2019COES...36....1J, 158187643, free, 10138/341512, free,

• Excess nutrients—phosphorus and nitrates—from fertilizers or sewage that are discharged to water bodies (also called nutrient pollution)WEB,weblink Climate Change and Harmful Algal Blooms, 2017-03-09, Nutrient Pollution, U.S. Environmental Protection Agency (EPA), Washington, D.C., JOURNAL, Amin, Md Nurul, Kroeze, Carolien, Strokal, Maryna, 2017, Human waste: An underestimated source of nutrient pollution in coastal seas of Bangladesh, India and Pakistan, Marine Pollution Bulletin, 118, 1–2, 131–140, 10.1016/j.marpolbul.2017.02.045, 28238487, 2017MarPB.118..131A, 0025-326X,
• climate change
• thermal pollution 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 mussels, Dreissena polymorpha—which preferentially eat non-toxic algae, competitors to harmful algaeJOURNAL, Harke, Matthew J., Steffen, Morgan M., Gobler, Christopher J., Otten, Timothy G., Wilhelm, Steven W., Wood, Susanna A., Paerl, Hans W., A review of the global ecology, genomics, and biogeography of the toxic cyanobacterium, Microcystis spp., Harmful Algae, Elsevier, 54, 2016, 1568-9883, 10.1016/j.hal.2015.12.007, 4–20, 28073480, free,

Nutrients

{{Further|Eutrophication}}Nutrients enter freshwater or marine environments as surface runoff from agricultural pollution and urban runoff from fertilized lawns, golf courses and other landscaped properties; and from sewage treatment plants that lack nutrient control systems.WEB,weblink Sources and Solutions, 2017-03-10, Nutrient Pollution, EPA, 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, 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.JOURNAL, 2010-01-01, Eutrophication and nutrient release in urban areas of sub-Saharan Africa — A review,weblink Science of the Total Environment, en, 408, 3, 447–455, 10.1016/j.scitotenv.2009.10.020, 0048-9697, Nyenje, P.M., Foppen, J.W., Uhlenbrook, S., Kulabako, R., Muwanga, A., 19889445, 2010ScTEn.408..447N, Residual nutrients in treated wastewater can also accumulate in downstream source water areasJOURNAL, 2013-05-15, A comparison of additional treatment processes to limit particle accumulation and microbial growth during drinking water distribution,weblink Water Research, en, 47, 8, 2719–2728, 10.1016/j.watres.2013.02.035, 0043-1354, Liu, G., Lut, M.C., Verberk, J.Q.J.C., Van Dijk, J.C., 23510692, 2013WatRe..47.2719L, 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.{{citation needed|date=January 2023}}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.{{citation needed|date=January 2023}}This contributes to the ongoing degradation of dams, lakes, rivers, and reservoirs - source water areas that are starting to become known as ecological infrastructure,WEB, • 'Ecological infrastructure' and 'green infrastructure',weblink 2021-09-22, biodiversityadvisor.sanbi.org, 2021-09-09,weblink" title="web.archive.org/web/20210909181200weblink">weblink dead, placing increasing pressure on wastewater treatment works and water purification plants. Such pressures, in turn, intensify seasonal HABs.{{citation needed|date=January 2023}}

Climate change

{{Further|Effects of climate change on oceans}}Climate change contributes to warmer waters which makes conditions more favorable for algae growth in more regions and farther north."Algal blooms 'likely to flourish as temperatures climb'", Straits Times, July 20, 2016 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 Â°C decade per decade between 1985 and 2009 due to global warming, also will likely increase algal blooming by 20% over the next century.JOURNAL, O'Reiley, etal, 2015, Rapid and highly variable warming of lake surface waters around the globe, Geophysical Research Letters, 42, 24, 10,773–10,781, 2015GeoRL..4210773O, 10.1002/2015GL066235, free, 10138/208854, free, 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 [H.-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. {{doi|10.1017/9781009157964.001}}.{{rp|16}} The is the result of human induced factors such as increased nutrient inputs (nutrient pollution) and climate change (in particular the warming of water temperatures).{{rp|16}} The parameters that affect the formation of HABs are ocean warming, marine heatwaves, oxygen loss, eutrophication and water pollution.Caretta, M.A., A. Mukherji, M. Arfanuzzaman, R.A. Betts, A. Gelfan, Y. Hirabayashi, T.K. Lissner, J. Liu, E. Lopez Gunn, R. Morgan, S. Mwanga, and S. Supratid, 2022: Chapter 4: Water. In: Climate Change 2022: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [H.-O. Pörtner, D.C. Roberts, M. Tignor, E.S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke, V. Möller, A. Okem, B. Rama (eds.)]. Cambridge University Press, Cambridge, UK and New York, NY, USA, pp. 551–712, {{doi|10.1017/9781009325844.006}}{{rp|582}}

Causes or contributing factors of coastal HABs

(File:Red tide.jpg|thumb|right|Coastal harmful algal bloom event.)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.WEB, Red Tide FAQ,weblink 2018-08-15, Texas Parks and Wildlife Department, Austin, TX, 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 provides an up-to-date status report on HABs in Florida.WEB, Red Tide Current Status Statewide Information,weblinkweblink" title="web.archive.org/web/20090822163316weblink">weblink 2009-08-22, 2009-08-23, Florida Fish and Wildlife Research Institute, The Texas Parks and Wildlife Department also provides a status report.WEB, Red Tide Index,weblink 2018-08-15, Texas Parks and Wildlife Department, While no particular cause of HABs has been found, many different factors can contribute to their presence. These factors can include water pollution, which originates from sources such as human sewage and agricultural runoff.WEB, West, L., 2016, Red Tide: Causes and Effects,weblink About News, 2022-04-10, 2017-03-02,weblink" title="web.archive.org/web/20170302113127weblink">weblink dead, 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)JOURNAL, Trainer, VL, Adams, NG, Bill, BD, Stehr, CM, Wekell, JC, Moeller, P, Busman, M, Woodruff, D, 2000, Domoic acid production near California coastal upwelling zones, June (1998), Limnol Oceanogr, 45, 8, 1818–1833, 2000LimOc..45.1818T, 10.4319/lo.2000.45.8.1818, free, 54007265, JOURNAL, Adams, NG, Lesoing, M, Trainer, VL, 2000, Environmental conditions associated with domoic acid in razor clams on the Washington coast, J Shellfish Res, 19, 1007–1015, while in others they appear to be a result of increased nutrient pollution from human activities.Lam CWY, Ho KC (1989) Red tides in Tolo Harbor, Hong Kong. In: Okaichi T, Anderson DM, Nemoto T (eds) Red tides. Biology, environmental science and toxicology. Elsevier, New York, pp 49–52. The growth of marine phytoplankton is generally limited by the availability of nitrates and phosphates, 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.JOURNAL, Walsh, et al, 2006, Red tides in the Gulf of Mexico: Where, when, and why?,weblink Journal of Geophysical Research, 111, C11003, 1–46, 2006JGRC..11111003W, 10.1029/2004JC002813, 2856968, 20411040, Some algal blooms on the Pacific Coast have also been linked to occurrences of large-scale climatic oscillations such as El Niño events.{{citation needed|date=January 2023}}

Other causes

Other factors such as iron-rich dust influx from large desert areas such as the Sahara are thought to play a role in causing HABs.JOURNAL, Walsh, etal, 2006, Red tides in the Gulf of Mexico: Where, when, and why?, Journal of Geophysical Research, 111, C11003, 1–46, 2006JGRC..11111003W, 10.1029/2004JC002813, 2856968, 20411040, Some algal blooms on the Pacific coast have also been linked to natural occurrences of large-scale climatic oscillations such as El Niño events. HABs are also linked to heavy rainfall.JOURNAL, Morse, Ryan E., Shen, Jian, Blanco-Garcia, Jose L., Hunley, William S., Fentress, Scott, Wiggins, Mike, Mulholland, Margaret R., Margaret Mulholland, 1 September 2011, Environmental and Physical Controls on the Formation and Transport of Blooms of the Dinoflagellate Cochlodinium polykrikoides Margalef in the Lower Chesapeake Bay and Its Tributaries, Estuaries and Coasts, 34, 5, 1006–1025, 10.1007/s12237-011-9398-2, 2011EstCo..34.1006M, 1559-2723, 84945112, Although HABs in the Gulf of Mexico were witnessed in the early 1500s by explorer Cabeza de Vaca,Cabeza de Vaca, Álvar Núnez. La Relación (1542). Translated by Martin A. dunsworth and José B. Fernández. Arte Público Press, Houston, Texas (1993) it is unclear what initiates these blooms and how large a role nanthropogenic and natural factors play in their development.{{citation needed|date=August 2023}}

Number and sizes

The number of reported harmful algal blooms (cyanobacterial) has been increasing throughout the world.REPORT, Field Manual of Wildlife Diseases, 1999, National Wildlife Health Center, United States Geological Survey (USGS), Madison, WI, 263, 0-607-88096-1, 1999-001, 2016-07-24,weblink" title="web.archive.org/web/20120905040143weblink">weblink 2012-09-05, Friend,weblink Milton, Ch. 36. Algal toxins, J. Christian, Franson, 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.JOURNAL, Sellner, K.G., Doucette G.J., Doucette, G.J., Kirkpatrick, 2003, Harmful Algal blooms: causes, impacts and detection, Journal of Industrial Microbiology and Biotechnology, 30, 7, 383–406, 10.1007/s10295-003-0074-9, 12898390, 6454310, free, JOURNAL, Van Dolah, F.M., 2000, Marine Algal Toxins: Origins, Health Effects, and Their Increased Occurrence,weblink Environmental Health Perspectives, 108, suppl.1, 133–141, 10.1289/ehp.00108s1133, 3454638, 1637787, 10698729,weblink" title="web.archive.org/web/20090120150050weblink">weblink 20 January 2009, 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" {{webarchive|url=https://web.archive.org/web/20170124175600weblink|date=2017-01-24}}, Office of Science and Technology Policy, Sept. 2008 The report recognized the seriousness of the problem:{{blockquote|It is widely believed that the frequency and geographic distribution of HABs have been increasing worldwide. All U.S. coastal states have experienced HABs over the last decade, and new species have emerged in some locations that were not previously known to cause problems. HAB frequency is also thought to be increasing in freshwater systems.}}Researchers have reported the growth of HABs in Europe, Africa and Australia. Those have included blooms on some of the African Great Lakes, such as Lake Victoria, the second largest freshwater lake in the world. India has been reporting an increase in the number of blooms each year."Boom in harmful algal blooms", The Hindu, Dec 20, 2010 In 1977 Hong Kong 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.NEWS, Toxic blue-green algae ends swimming at popular Victoria lake, en, CBC News,weblink 2017-10-23, 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,"NASA mission, led by Stanford biologist, finds massive algal blooms under Arctic sea ice", Stanford News, June 7, 2012 in Antarctica,"Behemoth Antarctic Algae Bloom Seen from Space", Life Science, March 7, 2012 the Himalayan Mountains,"Pollution, neglect and too much love killing once idyllic Himalayan lake", The Sydney Morning Herald, Nov. 5, 2011 the Rocky Mountains,"Addressing Algal Blooms in Rocky Mountain National Park", Jordan Ramis, August 6, 2015 and in the Sierra Nevada Mountains." Algae in Sierra Nevada Mountain Wilderness Areas: Potential Health Hazards", Journal of Mountain Medicine and Ecology, University of California, Davis, Fall 2009In 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 had a bloom which stretched an "unprecedented" {{convert|650|mi|km}} into adjoining states and tested positive for toxins, which created drinking water and recreation problems."Toxic algae bloom now stretches 650 miles along Ohio river" {{Webarchive|url=https://web.archive.org/web/20160809034951weblink |date=2016-08-09 }}, The Columbus Dispatch, Oct. 3, 2015 A portion of Utah's Jordan River was closed due to toxic algal bloom in 2016.Off the west coast of South Africa, HABs caused by Alexandrium catanella occur every spring. These blooms of organisms cause severe disruptions in fisheries of these waters as the toxins in the phytoplankton cause filter-feeding shellfish in affected waters to become poisonous for human consumption.WEB, Red Tide Fact Sheet - Red Tide (Paralytic Shellfish Poisoning),weblink live,weblink" title="web.archive.org/web/20090826001901weblink">weblink 26 August 2009, 2009-08-23, mass.gov,

Harmful effects

{{Further|Eutrophication#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."Spreading Dead Zones and Consequences for Marine Ecosystems", Science, August 15, 2008 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.NEWS, Dietrich, Tamara, 2016-07-19, Study: Chesapeake Bay a bigger methane generator than previously thought,weblink Daily Press, Newport News, VA, Scientists have found that HABs were a prominent feature of previous mass extinction events, including the End-Permian Extinction.JOURNAL, Mays, Chris, McLoughlin, Stephen, etal., September 17, 2021, Lethal microbial blooms delayed freshwater ecosystem recovery following the end-Permian extinction, Nature Communications, 12, 5511, 5511, 10.1038/s41467-021-25711-3, 34535650, 8448769, 2021NatCo..12.5511M, free,

Human health

Tests have shown some toxins near blooms can be in the air and thereby be inhaled, which could affect health."Tests Reveal Florida's Toxic Algae is Threatening Not Only The Water Quality but Also the Air", Weather.com, July 28, 2016

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 (ASP), diarrhetic shellfish poisoning, neurotoxic shellfish poisoning, and paralytic shellfish poisoning. 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.JOURNAL, Hoagland P., Anderson D.M., Kaoru Y., White A.W., August 2002, The Economic Effects of Harmful Algal Blooms in the United States: Estimates, Assessment Issues, and Information Needs, Estuaries, 4b, 2, 307–312, 258443, In 1987 a new illness emerged: amnesic shellfish poisoning (ASP). People who had eaten mussels from Prince Edward Island were found to have ASP. The illness was caused by domoic acid, produced by a diatom found in the area where the mussels were cultivated.JOURNAL, Backer, Lorraine C., Fall 2017, Harmful Algal Blooms. At the interface between coast oceanography and human health,weblink Oceanography, 19, 2, 96, A 2013 study found that toxic paralytic shellfish poisoning in the Philippines during HABs has caused at least 120 deaths over a few decades."Lethal paralytic shellfish poisoning from consumption of green mussel broth, Western Samar, Philippines, August 2013", World Health Organization, Issue #2, April–June 2015 After a 2014 HAB incident in Monterey Bay, California, health officials warned people not to eat certain parts of anchovy, sardines, or crab caught in the bay.NEWS,weblink Toxic algae blooms killing sea birds, threaten humans, KSBW TV News, April 30, 2014, 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.JOURNAL, 2683400, 17218574, 10.1378/chest.06-1830, 131, 1, Aerosolized red-tide toxins (brevetoxins) and asthma, Chest, 187–94, Fleming LE, Kirkpatrick B, Backer LC, Bean JA, Wanner A, Reich A, Zaias J, Cheng YS, Pierce R, Naar J, Abraham WM, Baden DG, 2007, In 2018 agricultural officials in Utah 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.NEWS,weblink Effects of algal blooms continue to spread throughout Wasatch Front, KSL TV News, July 19, 2016,

Drinking water

File:Toxic Algae Bloom in Lake Erie.jpg|thumb|Satellite image of Lake ErieLake EriePersons 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."People got sick at Pyramid Lake before the state reported toxic algae bloom. Could it have been avoided?", San Gabriel Valley Tribune, July 18, 2016 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."Blue algae problems persist", Marysville Online, July 13, 2016In 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" {{Webarchive|url=https://web.archive.org/web/20160724120618weblink |date=2016-07-24 }}, 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."Dog dies on Russian River, tests positive for toxic algae" {{Webarchive|url=https://web.archive.org/web/20160817003023weblink |date=2016-08-17 }}, Sept. 3, 2015 Boiling the water at home before drinking does not remove the toxins.In August 2014 the city of Toledo, Ohio advised its 500,000 residents to not drink tap water as the high toxin level from an algal bloom in western Lake Erie 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"The Big-Ag-Fueled Algae Bloom That Won't Leave Toledo's Water Supply Alone", Mother Jones, August 5, 2016 and was forecast again for the summer of 2016."Lake Erie's Toxic Algae Bloom Forecast for Summer 2016", EcoWatch, June 13, 2016In 2004, a bloom in Kisumu Bay, which is the drinking water source for 500,000 people in Kisumu, Kenya, 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."Algae smother Chinese lake, millions panic", NBC News, May 31, 2007NEWS, Kahn, Joseph, 2007-10-14, In China, a Lake's Champion Imperils Himself,weblink New York Times, A smaller water shut-down in China affected 15,000 residents two years later at a different location.weblink" title="web.archive.org/web/20090812010232weblink">"Algal bloom in Central China reservoir affects drinking water of 15,000", Chinaview, July 8, 2009 Australia in 2016 also had to cut off water to farmers."Blue-green algal bloom chokes Murray, cuts water to farmers", The Age, March 9, 2016Alan Steinman of Grand Valley State University has explained that among the major causes for the algal blooms in general, and Lake Erie specifically, is because blue-green algae thrive with high nutrients, along with warm and calm water. 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.Video interview: Dr. Alan Steinman on Algal Blooms in Lake Erie 13 min.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.{{citation needed|date=January 2023}}In studies at the population level bloom coverage has been significantly related to the risk of non-alcoholic liver disease death.JOURNAL, Feng Zhang, Jiyoung Lee, Song Liang, CK Shum, 2015, Cyanobacteria blooms and non-alcoholic liver disease: evidence from a county level ecological study in the United States, Environ Health, 14, 1, 41, 10.1186/s12940-015-0026-7, 4428243, 25948281, free, 2015EnvHe..14...41Z,

Neurological disorders

Toxic algae blooms are thought to play a role in humans developing degenerative neurological disorders such as amyotrophic lateral sclerosis and Parkinson's disease.NEWS, Konkel, Lindsey, Are Algae Blooms Linked to Lou Gherig's Disease,weblink 18 August 2021, Scientific American, December 11, 2014, 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 (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 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.JOURNAL, Backer, Lorraine C, Fleming, Lora E, Rowan, Alan, Cheng, Yung-Sung, Benson, Janet, Pierce, Richard H, Zaias, Julia, Bean, Judy, Bossart, Gregory D, March 2003, Recreational exposure to aerosolized brevetoxins during Florida red tide events, Harmful Algae, 2, 1, 19–28, 10.1016/s1568-9883(03)00005-2, 1568-9883, 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.JOURNAL, 10.1007/s10646-008-0241-x, 18758951, 2683401, Harmful algal toxins of the Florida red tide (Karenia brevis): Natural chemical stressors in South Florida coastal ecosystems, Ecotoxicology, 17, 7, 623–631, 2008, Pierce, R. H., Henry, M. S., 2008Ecotx..17..623P, 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.Pierce, R.H., M. S. Henry. "Harmful algal toxins of the Florida red tide (Karenia brevis): natural chemical stressors in South Florida coastal ecosystems." Ecotoxicology 2008; 623–631.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 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.JOURNAL, Van Dolah, F. M., 2000, Marine algal toxins: Origins, health effects, and their increased occurrence, Environmental Health Perspectives, 108, Suppl 1, 133–141, 10.1289/ehp.00108s1133, 3454638, 1637787, 10698729, 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, 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.Fleming LE, Kirkpatrick B, Backer LC, et al. Initial evaluation of the effects of aerosolized Florida red tide toxins (brevetoxins) in persons with asthma. Environ Health Perspect. 2005;113:650–657. People with severe or persistent respiratory conditions (such as chronic lung disease or asthma) may experience stronger adverse reactions.{{medical citation needed|date=July 2023}}The National Oceanic and Atmospheric Administration's National Ocean Service provides a public conditions report identifying possible respiratory irritation impacts in areas affected by HABs.WEB,weblink Harmful Algal Bloom Operational Forecast System, www.tidesandcurrents.noaa.gov/hab/, 2012-02-14, 2012-02-17,weblink" title="web.archive.org/web/20120217061645weblink">weblink dead,

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,"Summer conditions growing toxic algae blooms in two California lakes", Los Angeles Times, July 21, 2016 Vermont,"Vt. Beaches Reopen After Algae Blooms Clear", NECN, July 15, 2016 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, Minnesota, Utah, California and Ohio have had signs posted warning about the potential of health risk."Algae is blooming in waterways all around the country", Florida Today, July 22, 2016Similar blooms have become more common in Europe, with France among the countries reporting them. In the summer of 2009, beaches in northern Brittany 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."Lethal algae take over beaches in northern France", The Guardian, U.K., August 10, 2009The 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, 2016In port cities in the Shandong Province 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,"China hit by largest-ever algae bloom", Phys.org, July 4, 2013 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."Slimy green algae is taking over China's beaches for an alarming reason", Business Insider, July 13, 2015

Fisheries industry

As early as 1976 a short-term, relatively small, dead zone off the coasts of New York and New Jersey 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.NEWS, Miner, Colin, 2009-11-27, Assessing Algal Blooms' Economic Impact,weblink New York Times, Green: Energy, the Environment and the Bottom Line (blog), 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:WEB,weblink What is a harmful algal bloom?, 2016-04-27, U.S. National Oceanic and Atmospheric Administration (NOAA), Washington, D.C., $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 2000The 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.BOOK, Algae bloom and its economic impact, Sanseverino, Isabella, JRC publications, 2016, 978-92-79-58101-4, Europe, 23, 26, 27, 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....""Biggest-ever toxic algal bloom hits West Coast, shutting down shellfish industries", Oregon Live, June 16, 2015 The bloom covered a range from Santa Barbara, California northward to Alaska."Toxic algae bloom in Pacific Ocean could be largest ever", CBS News, June 17, 2015The 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 lost 260 tons of salmon as a result of blooms,Algae Blooms in fish farming, Farmed and Dangerous.org and in 2016 a farm in Chile lost 23 million salmon after an algal bloom."One Of The U.S.'s Top Salmon Providers Just Lost Millions Of Salmon", Climate Progress, March 10, 2016

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.JOURNAL, Joyce, S., 2000-03-01, The dead zones: oxygen-starved coastal waters., Environmental Health Perspectives, 108, 3, A120–A125, 10.1289/ehp.108-a120, 1637951, 10706539, 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 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, which returned to normal fairly quickly after the collapse of the Soviet Union in the 1990s due to a resulting reduction in fertilizer use.{{multiple image| align = left| direction = horizontal| image1 = Scientists discover under-ice phytoplankton bloom 1.ogv| width1 = 300| alt1 =| caption1 = The US Coast Guard Cutter Healy ferried scientists to 26 study sites in the Arctic, where blooms ranged in concentration from high (red) to low (purple).| image2 = Scientists discover under-ice phytoplankton bloom 2.ogv| width2 = 300| alt2 =| caption2 = Researcher David Mayer of Clark University lowers a video camera below the ice to observe a dense bloom of phytoplankton.}}{{clear}}

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."23 Million Salmon Dead Due to Toxic Algal Bloom in Chile", 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 and the creation of dead zones.Brown, Lester R. Plan B 4.0: Mobilizing to Save Civilization, Earth Policy Institute, p. 227Other countries have reported similar impacts, with cities such as Rio de Janeiro, 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 has suffered from harmful algal blooms, most recently in 2015: "Periodic blooms of toxin-producing Pseudo-nitzschia 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."Tim Stephens, Large bloom of toxic algae under way in Monterey Bay and beyond, UC Santa Cruz (June 2, 2015). Similar fish die-offs from toxic algae or lack of oxygen have been seen in Russia,"Kamensk local authorities have hired contractors to clean up mountains of dead fish from the beaches", July 18, 2016 Colombia,"Fish kills reported in the Palafitos", W Radio, July 17, 2016 Vietnam,"Thanh Hoa: Locals wear masks as smell from dead fish overpowering", Vietnam.net, July 19, 2016 China,"Hongze Lake Suqian great, full of dead fish breeding area", Modern Express Network, July 6, 2016 Canada,"Massive fish kill in Quebec's Yamaska River puzzle scientists", Digital Journal, July 4, 2016 Turkey,"Scores of starfish wash ashore in Turkey's northwest", Hurriyet Daily News, June 28, 2016 Indonesia,"90 Tons of Fish Die Darma Masal" {{Webarchive|url=https://web.archive.org/web/20160816150743weblink |date=2016-08-16 }}, Radar Cirebon, June 2, 2016 and France."Maine-et-Loire: Thousands of fish suffocated with the decline", France TV, June 18, 2016

Land animal deaths

Land animals, including livestock and pets have been affected. Dogs have died from the toxins after swimming in algal blooms."Unseasonal Toxic Algae Bloom In California Lake Kills Three Dogs", Climate Progress, Feb. 2, 2015 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.""Blue-green algal poisoning of stock" {{Webarchive|url=https://web.archive.org/web/20180620104157weblink |date=2018-06-20 }}, Agriculture Victoria(File:Dead whale NOAA.jpg|thumb|left|Whales can be killed by harmful algal blooms)Marine mammals have also been seriously harmed, as over 50 percent of unusual marine mammal deaths are caused by harmful algal blooms.WEB,weblink Over 50 percent of unusual marine mammal mortality events are caused by harmful algal blooms., 2007-02-13, Coastal Ecosystem Research, NOAA, In 1999, over 65 bottlenose dolphins died during a coastal HAB in Florida.WEB,weblink Harmful Algal Blooms, 2000-02-15, State of the Coastal Environment, NOAA, 2016-07-24, 2011-07-27,weblink" title="web.archive.org/web/20110727002805weblink">weblink dead, In 2013 a HAB in southwest Florida killed a record number of Manatee."Red Tide Algae Bloom Kills Record Number of Manatee" {{Webarchive|url=https://web.archive.org/web/20160816185353weblink |date=2016-08-16 }}, Accuweather, March 13, 2013 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."Algal Blooms Linked to Largest Die-Off of Great Whales Ever Recorded", EcoWatch, Oct. 29, 2015 In 2003 off Cape Cod in the North Atlantic, at least 12 humpback whales died from toxic algae from a HAB."Toxic algae suspected in whale death", Nature, August 4, 2003 In 2015 Alaska and British Columbia reported many humpback whales 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."30 Dead Whales Wash Ashore In Alaska; Scientists Commence Investigations", Nigerian News, August 24, 2015"Toxic Algae Could Be Killing Dozens of Whales", Inverse, Sept. 16, 2015Birds have died after eating dead fish contaminated with toxic algae. Rotting and decaying fish are eaten by birds such as pelicans, seagulls, cormorants, 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 scoters, 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,JOURNAL, Gramling C., 2017, Toxic algae may be culprit in mysterious dinosaur deaths, Science, 357, 6354, 857, 28860363, 10.1126/science.357.6354.857-a, 2017Sci...357..857G, such as the dozens of cetacean skeletons found at Cerro Ballena.JOURNAL, Pyenson, N. D., Gutsein, C. S., Parham, J. F., Le Roux, J. P., Chavarria, C. C., Little, H., Metallo, A., Rossi, V., Valenzuela-Toro, A. M., Velez-Juarbe, J., Santelli, C. M., Rogers, D. R., Cozzuol, M. A, Suárez, M. E., 2014, Repeated mass strandings of Miocene marine mammals from Atacama Region of Chile point to sudden death at sea, Proceedings of the Royal Society B: Biological Sciences, 281, 1781, 10.1098/rspb.2013.3316, free, 3953850, 24573855, Supplemental Material

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 with high levels of brevetoxin.JOURNAL, Flewelling, L. J., etal, 2005, Red tides and marine mammal mortalities, Nature (journal), Nature, 435, 7043, 755–756, 2005Natur.435..755F, 10.1038/nature435755a, 2659475, 15944690, 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, have been exposed to neurotoxins by preying on highly contaminated zooplankton.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. 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. 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.JOURNAL, Walsh, C. J., etal, 2010, Effects of brevetoxin exposure on the immune system of loggerhead sea turtles, Aquatic Toxicology, 97, 4, 293–303, 10.1016/j.aquatox.2009.12.014, 20060602, Examples of common harmful effects of HABs include:

1. the production of neurotoxins which cause mass mortalities in fish, seabirds, sea turtles, and marine mammals
2. human illness or death from consumption of seafood contaminated by toxic algaeWEB, Red Tide FAQ - Is it safe to eat oysters during a red tide?,weblink 2009-08-23, Tpwd.state.tx.us,
3. mechanical damage to other organisms, such as disruption of epithelial gill tissues in fish, resulting in asphyxiation
4. oxygen depletion of the water column (hypoxia or anoxia) from cellular respiration and bacterial degradation

(File:Gulf dead zone.jpg|thumb|Dead zone in the southern U.S.)

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 produced by these organisms. Saxitoxin blocks sodium channels and ingestion can cause paralysis within 30 minutes.WEB,weblink Red Tide FAQ – Is it safe to eat oysters during a red tide?, www.tpwd.state.tx.us, 2009-08-23, In addition to directly harming marine animals and vegetation loss, harmful algal blooms can also lead to ocean acidification, 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.US Department of Commerce, N. O. and A. A. (NOAA). (2019, April 2). What is Eutrophication? NOAA's National Ocean Service. Retrieved July 9, 2022, fromweblink animals that eat exposed shellfish are susceptible to the neurotoxin, which may lead to neurotoxic shellfish poisoningJOURNAL, Sharon M., Watkins, Andrew, Reich, Lora E., Fleming, Roberta, Hammond, Neurotoxic Shellfish Poisoning, Marine Drugs, 2008, 6, 3, 431–455, 10.3390/md20080021, 19005578, 2579735, free, 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, for example, are diving ducks 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 dolphins, sea turtles, birds, and manatees.WEB,weblink Red Tide & Red Algae Effects, 2015, WEB,weblink Top 10 Red Tide Facts, Florida Department of Health, 2016, 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 other 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.Hall-Scharf , B., & Ubeda , A. J. (2019, October 3). SG188/SG188: How red tides impact manatees. Retrieved July 10, 2022, fromweblink 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.JOURNAL, Landsberg, J.H., Flewelling, L.J., Naar, J., March 2009, Karenia brevis red tides, brevetoxins in the food web, and impacts on natural resources: Decadal advancements, Harmful Algae, 8, 4, 598–607, 10.1016/j.hal.2008.11.010, 1568-9883, In addition to causing manatee mortalities, red-tide exposure also causes severe 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.JOURNAL, Cook, P.F., Reichmuth, C., 2015, Algal toxin impairs sea lion memory and hippocampal connectivity, with implications for strandings,weblink Science, 350, 6267, 1545–1547, 10.1126/science.aac5675, 26668068, 2015Sci...350.1545C, 22981507,

Potential remedies

{{Further|eutrophication#Reversal and remediation}}

Reducing nutrient runoff

(File:Runoff of soil & fertilizer.jpg|thumb|Soil and fertilizer runoff from a farm after heavy rains)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, 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, 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.Siegel, Seth M. Let There Be Water: Israel's Solution for a Water-Starved World, Macmillan (2015) p. 66 Drip irrigation also prevents the formation of algal blooms in reservoirs for drinking water while saving up to 50% of water typically used by agriculture."Israel: Innovations overcoming water scarcity", OECD Observer, April 2015"How Israel survived its devastating drought", San Diego Union-Tribune, June 16, 2015There 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, 2004There 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 and along the Danube River 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.JOURNAL, Jeke, Nicholson N., Zvomuya, Francis, Cicek, Nazim, Ross, Lisette, Badiou, Pascal, September 2015, Biomass, Nutrient, and Trace Element Accumulation and Partitioning in Cattail (Typha latifolia L.) during Wetland Phytoremediation of Municipal Biosolids, Journal of Environmental Quality, 44, 5, 1541–1549, 10.2134/jeq2015.02.0064, 0047-2425, 26436271, free, 2015JEnvQ..44.1541J, JOURNAL, Cicek, N., Lambert, S., Venema, H.D., Snelgrove, K.R., Bibeau, E.L., Grosshans, R., June 2006, Nutrient removal and bio-energy production from Netley-Libau Marsh at Lake Winnipeg through annual biomass harvesting, Biomass and Bioenergy, 30, 6, 529–536, 10.1016/j.biombioe.2005.12.009, 2006BmBe...30..529C, 0961-9534, 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.WEB, 2015-10-01, The Floating Bioplatforms of IISD-ELA,weblink 2020-07-08, IISD Experimental Lakes Area, 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.REPORT,weblink National Nonpoint Source Program: A catalyst for water quality improvements, October 2016, EPA, EPA 841-R-16-009, {{rp|10}} WEB, 2018-07-25, NPDES Permit Basics,weblink National Pollutant Discharge Elimination System, EPA, By law, agricultural stormwater discharges and return flows from irrigated agriculture are not 'point sources.', WEB, Kozacek, Code, 2016-07-20, Algal Blooms Are No Accident For Florida Everglades and Estuaries,weblink Circle of Blue, Traverse City, Michigan, Locally developed initiatives to reduce nutrient pollution are underway in various areas of the country, such as the Great Lakes region and the Chesapeake Bay.WEB, 2016-08-29, Great Lakes Water Quality Agreement,weblink EPA, WEB, 2017-02-09, Chesapeake Bay Total Maximum Daily Load (TMDL),weblink EPA, To help reduce algal blooms in Lake Erie, the State of Ohio presented a plan in 2016 to reduce phosphorus runoff."Ohio plan to restore Lake Erie won't mandate farming changes" {{webarchive|url=https://web.archive.org/web/20160801131937weblink|date=2016-08-01}}, The Columbus Dispatch, July 27, 2016

Chemical treatment

Although a number of algaecides 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.JOURNAL, Zerrifi, Soukaina El Amrani, El Khalloufi, Fatima, Oudra, Brahim, Vasconcelos, Vitor, 2018-02-09, Seaweed Bioactive Compounds against Pathogens and Microalgae: Potential Uses on Pharmacology and Harmful Algae Bloom Control, Marine Drugs, 16, 2, 55, 10.3390/md16020055, 1660-3397, 5852483, 29425153, free, 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, 2015File:Efficacy of Aluminum Modified Clays.png|thumb|The left graph shows the efficacy of aluminum chloride modified clay (AC-MC), aluminum sulfide modified clay (AS-MC), polyaluminum modified clay (PAC-MC) and standard untreated clay in deionized water for removing Aureococcus anophagefferensAureococcus anophagefferensIn 2019, Chippewa Lake 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."Chippewa Lake becomes first testing site of new algae bloom technology produced by Israeli company", ABC News, Cleveland, OH August 27, 2019In February 2020, Roodeplaat Dam in Gauteng Province, South Africa was treated with a new algicide formulation against a severe bloom of Microcystis sp. This formulation allows the granular product to float and slow-release its active ingredient, sodium percarbonate, that releases hydrogen peroxide (H2O2), on the water surface. Consequently, the effective concentrations are limited, vertically, to the surface of the water; and spatially to areas where cyanobacteria 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.WEB, 2020-04-27, Israeli Company Successfully Treats Roodeplaat Dam of Toxic Algae Blooms,weblink 2020-04-27, Industry Leaders Magazine, 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, and Saccharina japonica 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, aluminum sulfate, 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 with the harmful algae cells. The algae cells then group together: becoming a sediment 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.JOURNAL, Liu, Yang, Cao, Xihua, Yu, Zhiming, Song, Xiuxian, Qiu, Lixia, 2016-02-15, Controlling harmful algae blooms using aluminum-modified clay,weblink Marine Pollution Bulletin, en, 103, 1, 211–219, 10.1016/j.marpolbul.2015.12.017, 0025-326X, 26763322, 2016MarPB.103..211L, In the Netherlands, successful algae and phosphate removal from surface water has been obtained by pumping affected water through a hydrodynamic separator. The treated water is then free from algae and contains a significant lower amount of phosphate since the removed algae cells contain a lot of phosphate. The treated water also gets a lower turbidity. Future projects will study the positive effects on the ecology and marine life as it is expected plant life will be restored and a reduction in bottom dwelling fish will automatically reduce the turbidity of the cleaned water. The removed algae and phosphate may find its way not as waste but as infeed to bio digesters.

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.WEB, 2017-03-02, Control and Treatment,weblink Nutrient Policy and Data, EPA,

Restoring shellfish populations

The decline of filter-feeding shellfish populations, such as oysters, likely contribute to HAB occurrence.WEB, Brumbaugh, R.D., et al, 2006, A Practitioners Guide to the Design & Monitoring of Shellfish Restoration Projects: An Ecosystem Approach. The Nature Conservancy, Arlington, Virginia,weblinkweblink" title="web.archive.org/web/20160304123652weblink">weblink 4 March 2016, 2017-03-18, Habitat.noaa.gov, As such, numerous research projects are assessing the potential of restored shellfish populations to reduce HAB occurrence.WEB, Shinnecock Bay Restoration Program,weblink 2017-03-18, Shinnecockbay.org, WEB, Delaware Oyster Gardening and Restoration - A Cooperative Effort,weblinkweblink" title="web.archive.org/web/20160304091603weblink">weblink 4 March 2016, 2017-03-18, Darc.cms.udel.edu, WEB, The Mobile Bay Oyster Gardening Program,weblinkweblink" title="web.archive.org/web/20130525040928weblink">weblink 25 May 2013, 5 August 2017,

Improved monitoring

{{multiple image| image1 = Super Blooms.ogv| width1 = 300| alt1 =| caption1 = Algal blooms forming and breaking up over time| direction = horizontal}}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.NEWS, Richtel, Matt, 2016-07-18, A Dreaded Forecast for Our Times: Algae, and Lots of It, New York Times,weblink One way they hope to do that is with sophisticated sensors which can help warn about potential blooms."Keeping Tabs on HABs: New Tools for Detecting, Monitoring, and Preventing Harmful Algal Blooms", Environmental Health Perspectives, August 1, 2014 The same types of sensors can also be used by water treatment facilities to help them prepare for higher toxic levels."Keeping Tabs on HABs: New Tools for Detecting, Monitoring, and Preventing Harmful Algal Blooms", Environmental Health Perspectives, August 2014The 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.WEB, 2016-12-20, Water System Security and Resilience in Homeland Security Research,weblink EPA, Satellite and remote sensing technologies are growing in importance for monitoring, tracking, and detecting HABs.JOURNAL, Anderson, Donald M., July 2009, Approaches to monitoring, control, and management of harmful algal blooms (HABs), Ocean and Coastal Management, 52, 7, 342–347, 10.1016/j.ocecoaman.2009.04.006, 2818325, 20161650, 2009OCM....52..342A, JOURNAL, Wu, Di, Zhang, Feiyang, Liu, Jia, March 9, 2019, A review on drone-based harmful algae blooms monitoring, Environmental Monitoring and Assessment, 191, 4, 211, 10.1007/s10661-019-7365-8, 30852736, 2019EMnAs.191..211W, 73725756, JOURNAL, Kim, Jun Song, Seo, Il Won, Baek, Donghae, May 2018, Modeling spatial variability of harmful algal bloom in regulated rivers using a depth-averaged 2D numerical model, Journal of Hydro-environment Research, 20, 63–76, 10.1016/j.jher.2018.04.008, 134289465, Four U.S. federal agencies—EPA, the National Aeronautics and Space Administration (NASA), NOAA, and the U.S. Geological Survey (USGS)—are working on ways to detect and measure cyanobacteria blooms using satellite data."US agencies creating algal bloom early warning system", Algae Industry Magazine, April 8, 2015 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" {{Webarchive|url=https://web.archive.org/web/20160722072709weblink |date=2016-07-22 }}, 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."Scientists Develop Early-Warning System for Toxic Algae Blooms" {{Webarchive|url=https://web.archive.org/web/20170107102300weblink |date=2017-01-07 }}, UVA Today, Univ. of Virginia, Jan. 4, 2017

Examples

Notable occurrences

• Lingulodinium polyedrum produces brilliant displays of bioluminescence in warm coastal waters. Seen in Southern California regularly since at least 1901.WEB, Nelson, Bryan, 2011-11-11, What is causing the waves in California to glow? &124; MNN - Mother Nature Network,weblink 2017-03-18, MNN,
• The largest algal bloom on record was the 1991 Darling River cyanobacterial bloom in Australia, largely of Anabaena circinalis, between October and December 1991 over {{convert|1000|km|mi|-1}} of the Barwon and Darling Rivers.JOURNAL, Bowling, L.C., Baker, P.D, 1996, Major Cyanobacterial Bloom in the Barwon-Darling River, Australia, in 1991, and Underlying Limnological Conditions, Marine and Freshwater Research, 47, 4, 643–657, 10.1071/MF9960643,
• 1530: First alleged case off the Florida Gulf Coast is without foundation.{{Citation |url=https://www.fs.fed.us/rm/boise/AWAE/scientists/profiles/Magana/HistoryKarenia%20brevis.pdf |title=A historical assessment of Karenia brevis in the western Gulf of Mexico|date=2018-08-16|language=en-US}} 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.WEB,weblink Log In or Sign Up to View, lookaside.fbsbx.com, en, 2018-07-21,
• 1793: The first recorded case occurring in British Columbia, Canada.WEB,weblink PARALYTIC SHELLFISH POISONING (PSP), Sabah Fish Department.com, 2013-01-11,
• 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.WEB,weblink Marine & Natural Resources – Red Tide & Fish Kill Resources – Taylor County Extension Office, 18 October 2016,
• 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.WEB,weblink The Punta Gorda herald. [volume] (Punta Gorda, Fla.) 1893-1958, December 07, 1916, Image 1, National Endowment for the, Humanities, December 7, 1916, chroniclingamerica.loc.gov,
• 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.NEWS, SHT Staff Writer, Red-tide timeline, 11 April 2022,weblinkweblink Sarasota Herald-Tribune, July 16, 2006,
• 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.WEB,weblinkweblink" title="web.archive.org/web/20081211004726weblink">weblink HAB 2000, December 11, 2008,
• 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.WEB,weblink Shellfish Poisoning in the South Pacific, MacLean, J.L., February 1974, South Pacific Commission,
• In 1972, a red tide was caused in New England by a toxic dinoflagellate Alexandrium (Gonyaulax) tamarense.WEB, HAB 2000,weblinkweblink" title="web.archive.org/web/20081211004726weblink">weblink 11 December 2008, utas.edu.au,
• 1976: The first PSP case in Sabah, Malaysian Borneo where 202 victims were reported to be suffering and 7 deaths.NEWS,weblink Red tide warning, 2013-01-07, 2013-01-06, New Straits Times,weblink" title="web.archive.org/web/20130107005300weblink">weblink 2013-01-07, NEWS,weblink 2 Red Tide deaths in Sabah, 2013-01-11, 2013-01-06, Daily Express (Sabah), Daily Express,
• 1987: A red algae bloom in Prince Edward Island caused over a million dollars in losses.WEB, Red Tides,weblink October 3, 2020,
• 2005: The Canadian red tide was discovered to have come further south than it has in years prior by the ship (R/V) Oceanus,WEB,weblink R/V Oceanus Archived Information, 18 October 2016, closing shellfish beds in Maine and Massachusetts and alerting authorities as far south as Montauk (Long Island, NY) to check their beds.WEB,weblink Moore, Kirk, Northeast Oysters: The bigger danger, growers assert, would be the label of endangered, National Fisherman, 2008-07-31,weblink" title="web.archive.org/web/20070808213003weblink">weblink 2007-08-08, 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.NEWS, Chrisafis, Angelique, 10 August 2009, Lethal algae take over beaches in northern France, The Guardian, London,weblink
• In 2010, dissolved iron in the ash from the Eyjafjallajökull volcano triggered a plankton bloom in the North Atlantic.NEWS, 10 April 2013, Iceland volcano ash cloud triggers plankton bloom, BBC News,weblink
• 2011: Northern CaliforniaNEWS,weblink The San Francisco Chronicle, Peter, Fimrite, 2011-09-17, Red tide killing abalone off California,
• 2011: Gulf of MexicoNEWS,weblink Huffington Post, Texas Gulf Coast Sees Largest Algae Bloom in Over A Decade, 2011-10-18,
• In 2013, an algal bloom was caused in Qingdao, China, by sea lettuce.NEWS, Jacobs, Andrew, 5 July 2013, Huge Algae Bloom Afflicts Coastal Chinese City, The New York Times,weblink
• 2013: In January, a red tide occurred again on the West Coast Sea of Sabah in the Malaysian Borneo.NEWS,weblink Sabah issues red tide alert, 2013-01-07, MUGUNTAN VANAR, 2013-01-07, The Star (Malaysia), The Star Online,weblink" title="web.archive.org/web/20130108194051weblink">weblink 2013-01-08, Two human fatalities were reported after they consumed shellfish 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.WEB,weblink UPDATE: Red tide, fish kill reported at Sarasota beaches, J. David, McSwane, 18 October 2016, 12 October 2015,weblink" title="web.archive.org/web/20151012181028weblink">weblink dead,
• In 2014, Myrionecta rubra (previously known as Mesodinium rubrum), a ciliate protist that ingests cryptomonad algae, caused a bloom in southeastern coast of Brazil.WEB, 2014-01-30, A Dark Bloom in the South Atlantic: Image of the Day,weblink 2017-03-18, Earthobservatory.nasa.gov,
• In 2014, blue green algae caused a bloom in the western basin of Lake Erie, poisoning the Toledo, Ohio water system connected to 500,000 people.NEWS, Tanber, George, 2014-08-02, Toxin leaves 500,000 in northwest Ohio without drinking water, Reuters,weblink live, 2017-03-18,weblink" title="web.archive.org/web/20150924203159weblink">weblink 24 September 2015,
• 2014: In August, massive 'Florida red tide' {{convert|90|mi}} long and {{convert|60|mi}} wide.NEWS,weblink Massive 'Florida red tide' is now 90 miles long and 60 miles wide, Orlando Sentinel, 11 August 2014, 30 September 2015, Netburn, Deborah,
• 2015: June, 12 persons hospitalized in the Philippine province of Bohol for red tide poisoning.WEB,weblink 12 persons hospitalized in Bohol for red tide poisoning, June 25, 2015, Israel, Dale G.,
• 2015: August, several beaches in the Netherlands between Katwijk and Scheveningen were plagued. Government institutions dissuaded swimmers from entering the water.WEB,weblink Rijkswaterstaat, do not swim between Katwijk and Scheveningen, Dutch Public Broadcasting, NOS, 3 August 2015, 30 September 2015,
• 2015: September, a red tide bloom occurred in the Gulf of Mexico, affecting Padre Island National Seashore along North Padre Island and South Padre Island in Texas.WEB,weblink Red Tide in Texas, Current Status, 15 September 2015, Texas Parks and Wildlife, 30 September 2015,
• 2017 and 2018: K. brevis red tide algae with warnings not to swim, state of emergency declared, dead dolphin and manatee, worsened by Caloosahatchee River. Peaked in the summer of 2018. Toxic harmful algae bloom red tide in Southwest Florida.NEWS,weblink Algae, red tide impacting SWFL water quality, 2018-07-04, WINK NEWS, 2018-07-05, en-US, NEWS,weblink Toxic Algae Blooms, Red Tide, and the Need for a Permanent Solution, Glenn, Julie, 2018-07-05, en, WEB,weblink What forms of nutrients can Karenia brevis use to grow and bloom?, myfwc.com, en, 2018-08-14, {{Dead link|date=September 2023 |bot=InternetArchiveBot |fix-attempted=yes }} A rare harmful algal bloom along Florida's east coast of Palm Beach County occurred the weekend of September 30, 2018.WEB,weblink Red tide confirmed off Palm Beach in rare outbreak for Florida's east coast, Miami Herald,
• In 2019, blue-green algae, or Cyanobacteria blooms,WEB, US Department of Commerce, NOAA, Lake Erie Harmful Algal Bloom,weblinkweblink 12 August 2019, 2019-08-22, www.weather.gov, 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.NEWS, Sacheli, Sarah, 8 August 2019, UWindsor researchers test the waters for harmful algae bloom, DailyNews, University of Windsor,weblinkweblink" title="web.archive.org/web/20190812145246weblink">weblink 12 August 2019, The largest Lake Erie bloom to date occurred in 2015, exceeding the severity index at 10.5 and in 2011 at a 10.NEWS, Hill, Sharon, 7 August 2019, Large Lake Erie algal bloom nearing Colchester tested for toxicity, Windsor Star,weblink 22 August 2019,weblink 11 August 2019, A large bloom does not necessarily mean the cyanobacteria ... will produce toxins", said Michael McKay, of the University of Windsor. 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 since the early 2000s.NEWS, The Hindu Net Desk, 2019-08-19, What caused the blue glow on Chennai beaches?, The Hindu,weblink 22 August 2019, 0971-751X,
• 2021: In July, a large red tide occurred on the Gulf Coast of Florida in and around Tampa Bay. The event has caused the death of millions of pounds of fish,WEB, 2021-07-23, Pinellas County already matches 2018 fishkill by cleaning up over 3 million pounds of dead fish,weblink 2021-07-27, WFTS, en, and led to the National Weather Service declaring a Beach Hazard.WEB, National Weather Service issues beach hazard statement over red tide concerns,weblink 2021-07-27, wtsp.com, 23 July 2021, en-US,
• 2021: in October, the 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.NEWS, North East coast shellfish deaths blamed on harmful algae,weblink 13 November 2022, BBC News, 3 February 2022, NEWS, Update on investigation into the deaths of crabs and lobster in the North East,weblink 13 November 2022, GOV.UK, 3 February 2022, en,
• 2023: A blue-green algae bloom occurred in Lough Neagh, Northern Ireland, the largest flesh water lake in the UK and Ireland were 40% of Northern Ireland gets its tap water from. It is caused by Northern Ireland experiencing both the wettest and hottest summer on record making conditions perfect for blue-green algae. Poor management of the Lough is being blammed. The bloom has killed dogs and wildlife, including swans.NEWS, Lough Neagh: What does future hold for UK's largest freshwater lake?,weblink 13 September 2023, BBC News, 10 September 2023,

United States

In July 2016 Florida 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."How Florida's Toxic Algae is Choking the Economy And The Environment", Nature World News, July 19, 2016 Some beaches were closed, and hotels and restaurants suffered a drop in business. Tourist sporting activities such as fishing and boating were also affected."Florida Tourism Not Seeing Green as Toxic Algae Chokes Business", NBC News, July 11, 2016"Toxic algae driving away Florida beachgoers", CNBC, July 5, 2016In 2019, the biggest Sargassum bloom ever seen created a crisis in the Tourism industry in North America. This event was likely caused by climate change and nutrient pollution from fertilizers.JOURNAL, Wang, Mengqiu, July 2019, The great Atlantic Sargassum belt, Science, 365, 6448, 83–87, 2019Sci...365...83W, 10.1126/science.aaw7912, 31273122, 195804245, free, 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.NEWS, Taylor, Alexandra, September 2019, Sargassum is strangling tourism in the Caribbean. Can scientists find a use for it?, Chemical & Engineering News,weblink April 21, 2021,

On the U.S. coasts

The Gulf of Maine frequently experiences blooms of the dinoflagellate Alexandrium fundyense, an organism that produces saxitoxin, the neurotoxin responsible for paralytic shellfish poisoning. The well-known "Florida red tide" that occurs in the Gulf of Mexico is a HAB caused by Karenia brevis, another dinoflagellate which produces brevetoxin, the neurotoxin responsible for neurotoxic shellfish poisoning. California coastal waters also experience seasonal blooms of Pseudo-nitzschia, a diatom known to produce domoic acid, the neurotoxin responsible for amnesic shellfish poisoning. File:Red tide＿2017.jpg|thumb|upright=1.2| Marine harmful algal bloom in a harbor, JapanJapanThe term red tide is most often used in the US to refer to Karenia brevis blooms in the eastern Gulf of Mexico, also called the Florida red tide. K. brevis is one of many different species of the genus Karenia found in the world's oceans.JOURNAL, Fleming, L.E., Kirkpatrick, B., Backer, L.C., Walsh, C.J., Nierenberg, K., Clark, J., etal, 2011, Review of Florida red tide and human health effects, Harmful Algae, 10, 2, 224–233, 10.1016/j.hal.2010.08.006, 3014608, 21218152, Major advances have occurred in the study of dinoflagellates and their genomics. Some include identification of the toxin-producing genes (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.Abraham and Baden, 2006; Backer et al., 2003a, 2005a; Backer and Fleming, 2008; Fleming et al., 2001; Fleming et al., 2004; Okamoto and Fleming, 2005; Twiner et al., 2008; Zaias et al., 2010.{{Full citation needed|date=August 2018}} 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 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.WEB, 2015, Red Tide (Paralytic Shellfish Poisoning),weblink Massachusetts Department of Public Health, Boston, MA, The related Alexandrium monilatum is found in subtropical or tropical shallow seas and estuaries in the western Atlantic Ocean, the Caribbean Sea, the Gulf of Mexico, and the eastern Pacific Ocean.

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.JOURNAL, Sharifan, Hamidreza, Ma, Xingmao, 2017-08-31, Potential Photochemical Interactions of UV Filter Molecules with Multichlorinated Structure of Prymnesins in Harmful Algal Bloom Events, Mini-Reviews in Organic Chemistry, 14, 5, 10.2174/1570193x14666170518124658,

Chesapeake Bay

File:July 12, 2013 - Sassafras River, VA Algal Bloom (9321804011).jpg|thumb|An algal bloom on the Sassafras RiverSassafras RiverThe Chesapeake Bay, the largest estuary in the U.S., has suffered from repeated large algal blooms for decades due to chemical runoff from multiple sources,"Scientists eye increase in harmful algae in Chesapeake", The Baltimore Sun, May 8, 2015 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."Too Much Nitrogen and Phosphorus Are Bad for the Bay" {{webarchive|url=https://web.archive.org/web/20160728141032weblink|date=2016-07-28}}, Chesapeake Bay Foundation, 2016 The population increase in the bay 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."Massive Nitrogen Pollution Accompanies China's Growth", Scientific American, Feb. 27, 2013"On Lake Taihu, China Moves To Battle Massive Algae Blooms", Environment 360, Yale University, July 21, 2011As 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%.WEB, 2016-07-27, Wastewater Pollution Reduction in the Chesapeake Bay Watershed,weblink EPA, 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 {{convert|64000|sqmi|km2}} watershed.WEB, 2016-09-29, Chesapeake Bay TMDL Fact Sheet,weblink EPA,

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.WEB, 2014-08-05, Toledo water crisis must spark serious environmental reforms, just as the burning Cuyahoga did, experts say,weblink WEB, 2014-10-04, Toxic Lake Erie algal blooms "reversible" experts say... But only if we stop the blame game and work together,weblink The International Joint Commission has called on United States and Canada to drastically reduce phosphorus loads into Lake Erie to address the threat.REPORT, International Joint Commission, Lake Erie Ecosystem Priority (LEEP), International Joint Commission, A balanced diet for Lake Erie: Reducing phosphorus loadings and harmful algal blooms, 2014, Washington, District of Columbia, 978-1-927336-07-6,weblinkweblink" title="web.archive.org/web/20180810045000weblink">weblink August 10, 2018, WEB, International Joint Commission,weblink Introducing the Report of the Lake Erie Ecosystem Priority (LEEP): highlights, 2014, 2018-08-08, 2018-08-06,weblink" title="web.archive.org/web/20180806151255weblink">weblink ijc.com, WEB, March 2014, Joint U.S.-Canada Agency Calls for Big Phosphorus Reductions in Lake Erie,weblink

Green Bay

Green Bay has a dead zone caused by phosphorus pollution that appears to be getting worse.NEWS, ((Associated Press)), Scientists: 'Dead zone' showing up in waters of Green Bay,weblink Twin Cities Pioneer Press, 15 August 2013,weblink August 18, 2020, (UPDATED: November 7, 2015),

Okeechobee Waterway

File:Cropped lake okeechobee oli 2016184 lrg.jpg|thumb|Harmful algal bloom (cyanobacteria) on Lake OkeechobeeLake OkeechobeeLake Okeechobee is an ideal habitat for cyanobacteria because its shallow, sunny, and laden with nutrients from Florida's agriculture.JOURNAL, Havens, Karl, Li, Bai-Lian, Philips, Edward, May 1998, Light availability as a possible regulator of cyanobacteria species composition in a shallow subtropical lake,weblink Freshwater Biology, 39, 3, 547–556, 10.1046/j.1365-2427.1998.00308.x, 1998FrBio..39..547H, Researchgate, The Okeechobee Waterway connects the lake to the Atlantic Ocean and the Gulf of Mexico through the St. Lucie River and the 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.WEB, Dr. Zack Jud On The Toxic Algae Crisis,weblink 2019-06-13, Stuart Magazine, en, {{Dead link|date=April 2024 |bot=InternetArchiveBot |fix-attempted=yes }}NEWS, Gomez, Melissa, 9 July 2018, Algae bloom in florida prompts fears about harm to health and economy, The New York Times,weblink 30 August 2018, Water draining from the lake filled the region with a noxious odor and caused respiratory problems in some humans during the following month.WEB, Di Liberto, Tom, 16 August 2018, Harmful algal blooms linger in parts of southern Florida in July and August 2018,weblink 30 August 2018, NOAA, To make matters worse, harmful red tide blooms are historically common on Florida's coasts during these same summer months.JOURNAL, Alcock, Frank, August 2007, An assessment of Florida red tide: causes, consequences, and management strategies.,weblink Mote Marine Technical Report, 1190, Mote Marine Laboratory, 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 and Port St. Lucie therefore experience the compounded effects of both types of harmful algal bloom. Cleanup crews hired by authorities in Lee County - where the Caloosahatchee meets the Gulf of Mexico - removed more than 1700 tons of dead marine life in August 2018.NEWS, Murphy, Paul, 23 August 2018, Florida's red tide has produced 2,000 tons of dead marine life and cost businesses more than $8 million, CNN,weblink 30 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.NEWS, August 2018, Toxic algae spreads in Baltic waters in biggest bloom in years, Reuters,weblink November 20, 2021, WEB, 4 January 2020, Lethal algae blooms – an ecosystem out of balance,weblink November 20, 2021, TheGuardian.com, This is seen by the Baltic Sea Action Group as a threat to biodiversity and regional fishing stocks.WEB, EUTROPHICATION IN THE BALTIC SEA,weblink November 20, 2021,

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 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

{{Authority control}}

- content above as imported from Wikipedia
- "Harmful algal bloom" does not exist on GetWiki (yet)
- time: 9:22am EDT - Sat, May 18 2024