Algal bloom
Overview
An algal bloom is a rapid increase or accumulation in the population of algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...

 (typically microscopic) in an aquatic system. Algal blooms may occur in freshwater as well as marine environments. Typically, only one or a small number of phytoplankton
Phytoplankton
Phytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτόν , meaning "plant", and πλαγκτός , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...

 species are involved, and some blooms may be recognized by discoloration of the water resulting from the high density of pigmented cells. Although there is no officially recognized threshold level, algae can be considered to be blooming at concentrations of hundreds to thousands of cells per milliliter, depending on the severity.
Encyclopedia
An algal bloom is a rapid increase or accumulation in the population of algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...

 (typically microscopic) in an aquatic system. Algal blooms may occur in freshwater as well as marine environments. Typically, only one or a small number of phytoplankton
Phytoplankton
Phytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτόν , meaning "plant", and πλαγκτός , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...

 species are involved, and some blooms may be recognized by discoloration of the water resulting from the high density of pigmented cells. Although there is no officially recognized threshold level, algae can be considered to be blooming at concentrations of hundreds to thousands of cells per milliliter, depending on the severity. Algal bloom concentrations may reach millions of cells per milliliter. Algal blooms are often green, but they can also be other colors such as yellow-brown or red, depending on the species of algae.

Bright green blooms are a result of cyanobacteria (colloquially known as blue-green algae) such as Microcystis
Microcystis aeruginosa
Microcystis aeruginosa is a species of freshwater cyanobacteria which can form harmful algal blooms that are of economic and ecological importance...

. Blooms may also consist of macroalgal (non-phytoplanktonic) species. These blooms are recognizable by large blades of algae that may wash up onto the shoreline.

Of particular note are harmful algal blooms (HABs), which are algal bloom events involving toxic or otherwise harmful phytoplankton such as dinoflagellate
Dinoflagellate
The dinoflagellates are a large group of flagellate protists. Most are marine plankton, but they are common in fresh water habitats as well. Their populations are distributed depending on temperature, salinity, or depth...

s of the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 Alexandrium and Karenia, or diatoms of the genus Pseudo-nitzschia. Such blooms often take on a red or brown hue and are known colloquially as red tide
Red tide
Red tide is a common name for a phenomenon also known as an algal bloom , an event in which estuarine, marine, or fresh water algae accumulate rapidly in the water column and results in discoloration of the surface water. It is usually found in coastal areas...

s
.

Freshwater algal blooms

Freshwater algal blooms are the result of an excess of nutrients, particularly phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...

. The excess of nutrients may originate from fertilizers that are applied to land for agricultural or recreational purposes, these nutrients can then enter watershed
Drainage basin
A drainage basin is an extent or an area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean...

s through water runoff. Excess carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

 and nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

 have also been suspected as causes.

When phosphates are introduced into water systems, higher concentrations cause increased growth of algae and plants. Algae tend to grow very quickly under high nutrient availability, but each alga is short-lived, and the result is a high concentration of dead organic matter which starts to decay. The decay process consumes dissolved oxygen in the water, resulting in hypoxic
Hypoxia (environmental)
Hypoxia, or oxygen depletion, is a phenomenon that occurs in aquatic environments as dissolved oxygen becomes reduced in concentration to a point where it becomes detrimental to aquatic organisms living in the system...

 conditions. Without sufficient dissolved oxygen in the water, animals and plants may die off
Dead zone (ecology)
Dead zones are hypoxic areas in the world's oceans, the observed incidences of which have been increasing since oceanographers began noting them in the 1970s. These occur near inhabited coastlines, where aquatic life is most concentrated...

 in large numbers.

Blooms may be observed in freshwater aquarium
Freshwater aquarium
A freshwater aquarium is a receptacle that holds one or more freshwater aquatic organisms for decorative, pet-keeping, or research purposes. Modern aquariums are most often made from transparent glass or acrylic glass. Typical inhabitants include fish, plants, amphibians, and invertebrates, such as...

s when fish are overfed and excess nutrients are not absorbed by plants. These are generally harmful for fish, and the situation can be corrected by changing the water in the tank and then reducing the amount of food given.

Harmful algal blooms

A harmful algal bloom (HAB) is an algal bloom that causes negative impacts to other organisms via production of natural toxins, mechanical damage to other organisms, or by other means. HABs are often associated with large-scale marine mortality events and have been associated with various types of shellfish poisoning
Shellfish poisoning
There are four syndromes called shellfish poisoning, which share some common features and are primarily associated with bivalve molluscs...

s.

Background

In the marine environment, single-celled, microscopic, plant-like organisms naturally occur in the well-lit surface layer of any body of water. These organisms, referred to as phytoplankton
Phytoplankton
Phytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτόν , meaning "plant", and πλαγκτός , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...

 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. 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.

Harmful algal blooms have been observed to cause adverse effects to varying species of marine mammals and sea turtles, with each presenting specific toxicity-induced reductions in developmental, immunological, neurological, and reproductive capacities. 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. 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. 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, via inhalation of aerosolized toxins and ingestion of contaminated prey, can have clinical signs of increased lethargy and muscle weakness in loggerhead sea turtles causing these animals to wash ashore in a decreased metabolic state with increases of immune system responses upon blood analysis.
Examples of common harmful effects of HABs include:
  1. the production of neurotoxins which cause mass mortalities in fish, seabirds, sea turtles, and marine mammals
  2. human illness or death via consumption of seafood contaminated by toxic algae
  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


Due to their negative economic and health impacts, HABs are often carefully monitored.

HABs occur in many regions of the world, and in the United States are recurring phenomena in multiple geographical regions. The Gulf of Maine
Gulf of Maine
The Gulf of Maine is a large gulf of the Atlantic Ocean on the east coast of North America.It is delineated by Cape Cod at the eastern tip of Massachusetts in the southwest and Cape Sable at the southern tip of Nova Scotia in the northeast. It includes the entire coastlines of the U.S...

 frequently experiences blooms of the dinoflagellate
Dinoflagellate
The dinoflagellates are a large group of flagellate protists. Most are marine plankton, but they are common in fresh water habitats as well. Their populations are distributed depending on temperature, salinity, or depth...

 Alexandrium fundyense
Alexandrium fundyense
Alexandrium fundyense is a dinoflagellate. It produces toxins that induce paralytic shellfish poisoning , and is a common cause of red tide.-References:...

, an organism that produces saxitoxin
Saxitoxin
Saxitoxin is a neurotoxin naturally produced by certain species of marine dinoflagellates and cyanobacteria Saxitoxin (STX) is a neurotoxin naturally produced by certain species of marine dinoflagellates (Alexandrium sp., Gymnodinium sp., Pyrodinium sp.) and cyanobacteria Saxitoxin (STX) is a...

, the neurotoxin responsible for paralytic shellfish poisoning
Paralytic shellfish poisoning
Paralytic shellfish poisoning is one of the four recognized syndromes of shellfish poisoning, which share some common features and are primarily associated with bivalve mollusks . These shellfish are filter feeders and, therefore, accumulate toxins produced by microscopic algae, such as...

. The well-known "Florida red tide" that occurs in the Gulf of Mexico is a HAB caused by Karenia brevis
Karenia brevis
Karenia brevis is a marine dinoflagellate common in Gulf of Mexico waters, and is the organism responsible for Florida red tide, as well as red tide in Texas.-Description:K...

, another dinoflagellate which produces brevetoxin
Brevetoxin
Brevetoxin , or brevetoxins, are a suite of cyclic polyether compounds produced naturally by a species of dinoflagellate known as Karenia brevis...

, the neurotoxin responsible for neurotoxic shellfish poisoning
Neurotoxic shellfish poisoning
Neurotoxic Shellfish Poisoning is caused by the consumption of shellfish contaminated by breve-toxins or brevetoxin analogs.Symptoms in humans include vomiting and nausea and a variety of neurological symptoms such as slurred speech...

. California coastal waters also experience seasonal blooms of Pseudo-nitzschia, a diatom
Diatom
Diatoms are a major group of algae, and are one of the most common types of phytoplankton. Most diatoms are unicellular, although they can exist as colonies in the shape of filaments or ribbons , fans , zigzags , or stellate colonies . Diatoms are producers within the food chain...

 known to produce domoic acid
Domoic acid
Domoic acid , the neurotoxin that causes amnesic shellfish poisoning , also known as zombie acid, is a kainic acid analog, heterocyclic amino acid associated with certain harmful algal blooms.-Occurrence:...

, the neurotoxin responsible for amnesic shellfish poisoning
Amnesic shellfish poisoning
Amnesic shellfish poisoning is a human illness caused by consumption of the marine biotoxin called domoic acid. This toxin is produced naturally by marine diatoms belonging to the genus Pseudo-nitzschia and the species...

. Off the west coast of South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...

, HABs caused by Alexandrium catanella occur every spring. These blooms of organisms cause severe disruptions in fisheries
Fishery
Generally, a fishery is an entity engaged in raising or harvesting fish which is determined by some authority to be a fishery. According to the FAO, a fishery is typically defined in terms of the "people involved, species or type of fish, area of water or seabed, method of fishing, class of boats,...

 of these waters as the toxins in the phytoplankton cause filter-feeding shellfish
Shellfish
Shellfish is a culinary and fisheries term for exoskeleton-bearing aquatic invertebrates used as food, including various species of molluscs, crustaceans, and echinoderms. Although most kinds of shellfish are harvested from saltwater environments, some kinds are found only in freshwater...

 in affected waters to become poisonous for human consumption.

If the HAB event results in a high enough concentration of algae the water may become discoloured or murky, varying in colour from purple to almost pink, normally being red or green. Not all algal blooms are dense enough to cause water discolouration.

Red tides

Red tide
Red tide
Red tide is a common name for a phenomenon also known as an algal bloom , an event in which estuarine, marine, or fresh water algae accumulate rapidly in the water column and results in discoloration of the surface water. It is usually found in coastal areas...

 is a term often used to describe HABs in marine coastal areas, as the dinoflagellate species involved in HABs are often red or brown, and tint the sea water to a reddish color. The more correct and preferred term in use is harmful algal bloom, because:
  1. these blooms are not associated with tides
  2. not all algal blooms cause reddish discoloration of water
  3. not all algal blooms are harmful, even those involving red discolouration

Causes of HABs

It is unclear what causes HABs; their occurrence in some locations appears to be entirely natural, while in others they appear to be a result of human activities. Furthermore, there are many different species of algae that can form HABs, each with different environmental requirements for optimal growth. The frequency and severity of HABs in some parts of the world have been linked to increased nutrient loading from human activities. In other areas, HABs are a predictable seasonal occurrence resulting from coastal upwelling, a natural result of the movement of certain ocean currents. The growth of marine phytoplankton (both non-toxic and toxic) is generally limited by the availability of nitrates and phosphates, which can be abundant in coastal upwelling zones as well as in agricultural run-off. The type of nitrates and phosphates available in the system are also a factor, since phytoplankton can grow at different rates depending on the relative abundance of these substances (e.g. ammonia, 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
Water pollution
Water pollution is the contamination of water bodies . Water pollution occurs when pollutants are discharged directly or indirectly into water bodies without adequate treatment to remove harmful compounds....

 produced by humans and systematic increase in sea water temperature
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...

 have also been suggested as possible contributing factors in HABs. Other factors such as iron-rich dust influx from large desert areas such as the Sahara
Sahara
The Sahara is the world's second largest desert, after Antarctica. At over , it covers most of Northern Africa, making it almost as large as Europe or the United States. The Sahara stretches from the Red Sea, including parts of the Mediterranean coasts, to the outskirts of the Atlantic Ocean...

 are thought to play a role in causing HABs. Some algal blooms on the Pacific coast
Pacific Coast
A country's Pacific coast is the part of its coast bordering the Pacific Ocean.-The Americas:Countries on the western side of the Americas have a Pacific coast as their western border.* Geography of Canada* Geography of Chile* Geography of Colombia...

 have also been linked to natural occurrences of large-scale climatic oscillations such as El Niño events. While HABs in the Gulf of Mexico have been occurring since the time of early explorers such as Cabeza de Vaca, it is unclear what initiates these blooms and how large a role anthropogenic and natural factors play in their development. It is also 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.

Notable occurrences

  • In 1972 a red tide was caused in New England by a toxic dinoflagellate Alexandrium (Gonyaulax) tamarense.
  • In 2005 the Canadian HAB was discovered to have come further south than it has in years prior by a ship called The Oceanus, closing shellfish beds in Maine and Massachusetts and alerting authorities as far south as Montauk
    Montauk, New York
    Montauk [ˈmɒntɒk] is a census-designated place that roughly corresponds to the hamlet with the same name located in the town of East Hampton in Suffolk County, New York, United States on the South Shore of Long Island. As of the United States 2000 Census, the CDP population was 3,851 as of 2000...

     (Long Island
    Long Island
    Long Island is an island located in the southeast part of the U.S. state of New York, just east of Manhattan. Stretching northeast into the Atlantic Ocean, Long Island contains four counties, two of which are boroughs of New York City , and two of which are mainly suburban...

    , NY) to check their beds. Experts who discovered the reproductive cysts in the seabed warn of a possible spread to Long Island in the future, halting the area's fishing and shellfish industry and threatening the tourist trade, which constitutes a significant portion of the island's economy.
  • Brittany, in France, in 2009 was experiencing recurring algal booms caused by the high amount of fertilizer discharging in the sea due to intensive pig farming
    Intensive pig farming
    Intensive piggeries are a type of factory farm ' specialized in the raising of domestic pigs up to slaughter weight...

    , causing lethal gas emissions that have already killed.

See also

  • Algae fuel
    Algae fuel
    Algae fuel might be an alternative to fossil fuel and uses algae as its source of natural deposits. Several companies and government agencies are funding efforts to reduce capital and operating costs and make algae fuel production commercially viable...

  • Amnesic shellfish poisoning
    Amnesic shellfish poisoning
    Amnesic shellfish poisoning is a human illness caused by consumption of the marine biotoxin called domoic acid. This toxin is produced naturally by marine diatoms belonging to the genus Pseudo-nitzschia and the species...

  • Brevetoxin
    Brevetoxin
    Brevetoxin , or brevetoxins, are a suite of cyclic polyether compounds produced naturally by a species of dinoflagellate known as Karenia brevis...

  • Ciguatera
    Ciguatera
    Ciguatera is a foodborne illness caused by eating certain reef fishes whose flesh is contaminated with toxins originally produced by dinoflagellates such as Gambierdiscus toxicus which lives in tropical and subtropical waters. These dinoflagellates adhere to coral, algae and seaweed, where they are...

  • Cyanotoxin
    Cyanotoxin
    Cyanotoxins are toxins produced by bacteria called cyanobacteria . Cyanobacteria are found almost everywhere, but particularly in lakes and in the ocean where, under certain conditions, they reproduce exponentially to form blooms. Blooming cyanobacteria can produce cyanotoxins in such...

  • Dead zone (ecology)
    Dead zone (ecology)
    Dead zones are hypoxic areas in the world's oceans, the observed incidences of which have been increasing since oceanographers began noting them in the 1970s. These occur near inhabited coastlines, where aquatic life is most concentrated...

  • Dinoflagellate
    Dinoflagellate
    The dinoflagellates are a large group of flagellate protists. Most are marine plankton, but they are common in fresh water habitats as well. Their populations are distributed depending on temperature, salinity, or depth...

  • Domoic acid
    Domoic acid
    Domoic acid , the neurotoxin that causes amnesic shellfish poisoning , also known as zombie acid, is a kainic acid analog, heterocyclic amino acid associated with certain harmful algal blooms.-Occurrence:...

  • Emiliania huxleyi
    Emiliania huxleyi
    Emiliania huxleyi, often abbreviated "EHUX", is a species of coccolithophore with a global distribution from the tropics to subarctic waters. It is one of thousands of different photosynthetic plankton that freely drift in the euphotic zone of the ocean, forming the basis of virtually all marine...

  • Eutrophication
    Eutrophication
    Eutrophication or more precisely hypertrophication, is the movement of a body of water′s trophic status in the direction of increasing plant biomass, by the addition of artificial or natural substances, such as nitrates and phosphates, through fertilizers or sewage, to an aquatic system...

  • Iron fertilization
    Iron fertilization
    Iron fertilization is the intentional introduction of iron to the upper ocean to stimulate a phytoplankton bloom. This is intended to enhance biological productivity, which can benefit the marine food chain and remove carbon dioxide from the atmosphere. Iron is a trace element necessary for...

  • Milky seas effect
    Milky seas effect
    Milky seas is a condition on the open ocean where large areas of seawater are filled with bioluminescent bacteria, causing the ocean to uniformly glow an eerie blue at night...

  • Neurotoxic shellfish poisoning
    Neurotoxic shellfish poisoning
    Neurotoxic Shellfish Poisoning is caused by the consumption of shellfish contaminated by breve-toxins or brevetoxin analogs.Symptoms in humans include vomiting and nausea and a variety of neurological symptoms such as slurred speech...

  • Paralytic shellfish poisoning
    Paralytic shellfish poisoning
    Paralytic shellfish poisoning is one of the four recognized syndromes of shellfish poisoning, which share some common features and are primarily associated with bivalve mollusks . These shellfish are filter feeders and, therefore, accumulate toxins produced by microscopic algae, such as...

  • Pfiesteria
    Pfiesteria
    Pfiesteria is a genus of heterotrophic dinoflagellates that has been associated with harmful algal blooms and fish kills. Pfiesteria complex organisms were claimed to be responsible for large fish kills in the 1980s and 1990s on the coast of North Carolina and in tributaries of the Chesapeake Bay...

  • Phytoplankton
    Phytoplankton
    Phytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτόν , meaning "plant", and πλαγκτός , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...

  • Raphidophyte
    Raphidophyte
    Raphidophytes are a small group of eukaryotic algae that includes both marine and freshwater species. All raphidophytes are unicellular, with large cells but no cell walls. Raphidophytes possess a pair of flagella, organised such that both originate from the same invagination...

  • Saxitoxin
    Saxitoxin
    Saxitoxin is a neurotoxin naturally produced by certain species of marine dinoflagellates and cyanobacteria Saxitoxin (STX) is a neurotoxin naturally produced by certain species of marine dinoflagellates (Alexandrium sp., Gymnodinium sp., Pyrodinium sp.) and cyanobacteria Saxitoxin (STX) is a...

  • Shiro alga carta
    Shiro alga carta
    Shiro Alga Carta is a paper made from algae which would otherwise clog up the Venetian Lagoon. The algae, which are harvested annually, are used in partial substitution of pulp and are combined with FSC fibres.-History:...

  • Spring bloom
    Spring bloom
    The spring bloom is a strong increase in phytoplankton abundance that typically occurs in the early spring and lasts until late spring or early summer. This seasonal event is characteristic of temperate North Atlantic, sub-polar, and coastal waters...



External links

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