Toxigenic Algae And Algal Food Poisoning

Toxigenic algae are the microscopic algae which produce toxic substances. These may be some microalgae and cyanobacteria. They are found in freshwater, sea water and brackish water.

Under suitable condition, these algae multiply very fast. Warm temperature, stagnant or slow moving water and excess nutrients help in their growth. This rapid growth is called harmful algal bloom (HAB).

During bloom condition, some algae produce poisonous substances. These poisons are called marine biotoxins or phycotoxins. All algae are not toxic. Only small number of algal species are toxigenic and harmful to man and animals.

Algal food poisoning occurs when contaminated sea food is eaten by man or animals. The toxin enters into sea animals during algal bloom. Then these toxins are stored in their body tissues.

Filter feeding shellfishes are the main carrier of these toxins. Mussels, clams, oysters and scallops take toxic algal cells from water during feeding. The toxin become concentrated in their body and they may look normal from outside.

Some algal toxins also pass through the food chain. Small fishes or other animals take toxic algae. Then large carnivorous reef fishes eat them and toxin is accumulated in their body. This is common in some fish poisoning.

The important point is that these toxins are very stable. They are not destroyed by cooking, freezing, canning, pickling or smoking. So cooked sea food may also cause poisoning if it already contains algal toxin.

The major types of algal food poisoning are Paralytic Shellfish Poisoning (PSP), Amnesic Shellfish Poisoning (ASP), Diarrheic Shellfish Poisoning (DSP), Neurotoxic Shellfish Poisoning (NSP) and Ciguatera Fish Poisoning.

The symptoms depend on the type of toxin. It may cause nausea, vomiting, diarrhoea and abdominal pain. Some toxins affect nervous system and cause numbness, memory loss, muscle paralysis and even respiratory failure.

Thus toxigenic algae are important because they affect public health, fishery and marine food safety. Their bloom should be monitored in coastal and freshwater areas. Contaminated shellfish and fish should not be used as food.

Toxins Produced by Some Notable Algae

1. Alexandrium species
   Alexandrium ostenfeldii and Alexandrium peruvianum are toxic dinoflagellates. The toxins are saxitoxins, spirolides and gymnodimines. Saxitoxin is a paralytic shellfish toxin.
2. Azadinium species
   Azadinium spinosum and Azadinium poporum produce azaspiracids (AZAs). AZA-59 is also included in this toxin group. These are shellfish poisoning toxins.
3. Amphidoma species
   Amphidoma species also produce azaspiracids. These toxins are accumulated in shellfish. It causes poisoning after eating contaminated shellfish.
4. Dinophysis species
   Dinophysis species produce okadaic acid. Other toxins are dinophysistoxins (DTXs) and pectenotoxins (PTXs). These are mainly diarrheic shellfish toxins.
5. Gambierdiscus toxicus
   Gambierdiscus toxicus produces ciguatoxins and maitotoxin. These toxins enter into reef fishes. It causes ciguatera fish poisoning.
6. Gonyaulax spinifera
   Gonyaulax spinifera produces yessotoxins (YTXs). These toxins are found in marine shellfish. It is related with harmful algal bloom.
7. Lingulodinium polyedrum
   Lingulodinium polyedrum also produces yessotoxins. It is a marine dinoflagellate. The toxin may be accumulated in shellfish.
8. Protoceratium reticulatum
   Protoceratium reticulatum produces yessotoxins (YTXs). It is another yessotoxin producing dinoflagellate. It is important in shellfish toxicity.
9. Gymnodinium species
   Some Gymnodinium species produce saxitoxins. Gymnodinium cf. mikimotoi produces gymnodimines also. These are harmful algal toxins.
10. Karenia species
    Karenia brevis produces brevetoxins. Karenia selliformis produces gymnodimines. These toxins are important in marine algal poisoning.
11. Microcystis species
    Microcystis is a cyanobacteria or blue-green algae. It produces microcystins. These toxins are common in freshwater algal bloom.
12. Aphanizomenon flos-aquae
    Aphanizomenon flos-aquae is also a cyanobacterium. It produces microcystins. These toxins affect drinking water and aquatic animals.
13. Ostreopsis species
    Ostreopsis ovata, Ostreopsis siamensis, Ostreopsis mascarenensis and Ostreopsis lenticularis produce palytoxins. Other related toxins are ovatoxins, ostreocins and mascarenotoxins.
14. Prorocentrum species
    Prorocentrum lima and Prorocentrum maculosum produce okadaic acid and dinophysistoxins. They also produce prorocentrolides and spiro-prorocentrimine.
15. Pseudo-nitzschia species
    Pseudo-nitzschia is a diatom. It produces domoic acid. This toxin causes amnesic shellfish poisoning.
16. Symbiodinium species
    Symbiodinium produces symbioimine and neosymbioimine. These are toxins of symbiotic dinoflagellates. They are obtained from marine association.
17. Trichodesmium species
    Trichodesmium is a marine cyanobacterium. It produces palytoxins. It may form bloom in sea water.
18. Vulcanodinium rugosum
    Vulcanodinium rugosum produces pinnatoxins, portimines and kabirimine. These are cyclic imine type toxins. It is a toxic dinoflagellate.

Route of Exposure to Algal Food Poisoning

• Contaminated shellfish
  The main route is by eating contaminated shellfish. Mussels, oysters, clams and scallops filter the water. During this, toxic algal cells enter into their body and toxin is stored there.
• Contaminated fishes
  Some fishes also become toxic. The algal toxin passes from small organism to bigger fish through food chain. When these fishes are eaten, the toxin enters into human body.
• Other sea animals
  Crabs, lobsters, snails and other marine animals may also carry algal toxin. They get toxin from food or from contaminated water. Eating these animals may also produce poisoning.
• Blue-green algae supplements
  Some blue-green algae food supplements may contain toxins. The common toxin is microcystin. So contaminated supplement is also a route of exposure.
• Swallowing water
  Poisoning may occur by swallowing bloom water. It may happen during swimming or other water activity. The water may be fresh water, brackish water or sea water.
• Inhalation
  Some toxins come into air with sea spray. Brevetoxin and palytoxin may enter by breathing. This occurs near the area of harmful algal bloom.
• Skin contact
  Toxin may enter by direct contact with contaminated water. Skin irritation and other illness may occur. Handling toxic coral like Palythoa in aquarium may also expose the person.
• Important point
  Eating contaminated seafood is the most important route. The seafood may look normal. Cooking, freezing or washing does not always remove the algal toxin.

Toxicokinetics of Algal Toxins

1. Saxitoxins
   • Absorption – Saxitoxins are absorbed after eating contaminated shellfish. It may also enter by inhalation.
   • Distribution – It spreads quickly in the body. It may reach the brain also.
   • Metabolism – It is not mainly dependent on liver metabolism.
   • Elimination – It is removed mainly through urine. Kidney is the main route of excretion.
2. Brevetoxins
   • Absorption – Brevetoxins are absorbed quickly after exposure.
   • Distribution – It spreads in different tissues. Highest amount is found in liver.
   • Metabolism – Liver takes part in its processing.
   • Elimination – It is removed through urine and bile. In early stage, bile route is more important.
3. Domoic acid
   • Absorption – Domoic acid is poorly absorbed from intestine.
   • Distribution – After absorption, it spreads in the body.
   • Metabolism – It has less important metabolism in the body.
   • Elimination – It is mainly removed through faeces.
4. Okadaic acid
   • Absorption – Okadaic acid is well absorbed from gut.
   • Distribution – It becomes concentrated mainly in intestinal tissue.
   • Metabolism – It is metabolised by liver cytochrome P450 enzyme. Some reactive toxic products may be formed.
   • Elimination – It is removed through urine and faeces. It may also show enterohepatic circulation.
5. Yessotoxins
   • Absorption – Yessotoxins are poorly absorbed from gastrointestinal tract.
   • Distribution – Most of it remains in gut.
   • Metabolism – It is not changed much inside the body.
   • Elimination – It is mostly excreted unchanged through faeces.
6. Azaspiracids
   • Absorption – Azaspiracids can pass into tissues more easily due to special chemical nature.
   • Distribution – It can penetrate mammalian tissues.
   • Metabolism – Its detailed metabolism is not clearly given here.
   • Elimination – Its elimination is not clearly given here, but its tissue penetration property is important.

Mode of action of algal toxins and how they infect

Algal toxins are toxic chemical substances produced by some algae and cyanobacteria. They do not infect like bacteria, virus or fungi. They cause disease by intoxication, when toxin enters in body through contaminated food, water, air droplets or skin contact.

How algal toxins infect or enter in body

1. Formation of algal bloom
   Under suitable condition, toxin producing algae multiply very fast in water. Warm temperature, slow moving water and high nutrient pollution help in the formation of harmful algal bloom.
2. Production of toxin
   During this growth, some algae produce poisonous compounds. These toxins remain in water or inside the algal cells.
3. Entry into shellfish
   Filter feeding animals like mussels, oysters and clams take large amount of water. During filtration, toxic algal cells are accumulated in their tissues. These animals may not show disease.
4. Movement in food chain
   The toxins pass from small aquatic organisms to large fishes, reef fishes and crustaceans. This is called biomagnification. In this process toxin becomes more concentrated in the food chain.
5. Human exposure
   Human beings mainly affected by eating contaminated sea food. Sometimes toxin also enters by swallowing contaminated water, inhalation of sea spray and direct skin contact.
6. Intoxication in body
   After entry, toxin affects nerves, muscles, intestine, brain or cell membrane. This produces paralysis, vomiting, diarrhea, memory loss and sometimes death.

Mode of action of important algal toxins

1. Saxitoxin
   Saxitoxin causes paralytic shellfish poisoning. It binds with voltage gated sodium channel of nerve and muscle cells. So sodium ion cannot enter into cell. Nerve impulse is stopped and neuromuscular paralysis is produced.
2. Brevetoxin
   Brevetoxin causes neurotoxic shellfish poisoning. It also acts on voltage gated sodium channel. But it keeps the sodium channel open. Continuous entry of sodium takes place and nerve excitation occurs again and again.
3. Domoic acid
   Domoic acid causes amnesic shellfish poisoning. It acts like the neurotransmitter glutamate. It over stimulates kainate receptors in hippocampus region of brain. Calcium enters in large amount and memory related neurons are damaged.
4. Okadaic acid and dinophysistoxin
   Okadaic acid and dinophysistoxin cause diarrheic shellfish poisoning. They inhibit protein phosphatase enzymes. Due to this, regulation of cell protein is disturbed. Water and electrolytes move into intestine and severe diarrhea is produced.
5. Palytoxin
   Palytoxin is a very powerful toxin. It binds with sodium-potassium pump (Na⁺/K⁺-ATPase) of cell membrane. This pump is converted into open channel. Ion balance of cell is lost and cell death, hemolysis and violent muscle contraction takes place.
6. Cyclic imines
   Cyclic imines include gymnodimine, spirolide and pinnatoxin. They block nicotinic acetylcholine receptors of nerves and muscles. So normal nerve-muscle transmission is inhibited and rapid neurological dysfunction occurs.
7. Azaspiracid
   Azaspiracid causes azaspiracid shellfish poisoning. Its exact mechanism is not fully clear. It inhibits hERG voltage gated potassium channel and damages intestinal lining. It decreases cell viability and may produce progressive paralysis.
8. Yessotoxin
   Yessotoxin affects intracellular signalling system. It disturbs calcium, cAMP and mTOR signalling pathway. Due to this, programmed cell death like apoptosis, paraptosis and autophagy is started.

Acute and Chronic Toxicity of Algal Toxins

1. Microcystins
   • Source – Microcystins are produced by cyanobacteria or blue-green algae like Microcystis.
   • Acute toxicity – It causes nausea, vomiting, diarrhoea and abdominal pain. Dry cough, sore throat and blistering around mouth may also occur. In severe condition pneumonia may develop.
   • Chronic toxicity – Long time exposure may damage liver and kidney. The damage may be irreversible. Microcystins also act as tumour promoter and may cause hepatic carcinogenesis.
2. Domoic acid
   • Source – Domoic acid is produced by Pseudo-nitzschia. It is related with amnesic shellfish poisoning.
   • Acute toxicity – It causes vomiting, severe abdominal cramp and watery diarrhoea. Later headache, short term memory loss, seizure and cardiac arrhythmia may occur. Severe poisoning may lead to coma and death.
   • Chronic toxicity – Severe cases may cause permanent loss of short term memory. This occurs due to damage of hippocampus of brain. The memory defect may remain for long time.
3. Okadaic acid and Dinophysistoxins
   • Source – These toxins are produced by Dinophysis and Prorocentrum. They are related with diarrheic shellfish poisoning.
   • Acute toxicity – It causes profuse watery diarrhoea. Nausea, vomiting, abdominal pain, chill and fever are also present. Usually symptoms disappear within 72 hours.
   • Chronic toxicity – Long time damage is not common after acute attack. But okadaic acid may act as tumour promoter. It inhibits protein phosphatase and is carcinogenic in animal study.
4. Saxitoxins
   • Source – Saxitoxins are paralytic shellfish toxins. They are produced by some Alexandrium and Gymnodinium species.
   • Acute toxicity – Early symptoms are tingling and numbness of face and fingers. Headache, dizziness, ataxia and floating sensation may occur. Severe poisoning causes flaccid muscle weakness, respiratory distress and death by asphyxiation.
   • Chronic toxicity – If patient survives first 24 hours, recovery usually occurs within few days. Permanent neurological damage is generally absent.
5. Brevetoxins
   • Source – Brevetoxins are produced by Karenia brevis. It is related with neurotoxic shellfish poisoning.
   • Acute toxicity – After ingestion it causes diarrhoea, nausea and vomiting. Numbness of face and reversal of temperature feeling may occur. Cold object may feel hot.
   • Inhalation toxicity – When toxin comes as sea spray, it affects respiratory tract. It causes cough, wheezing and bronchoconstriction. It may be severe in asthmatic patient.
   • Chronic toxicity – No clear long term effect is fixed. But inhalation may aggravate asthma and COPD.
6. Azaspiracids
   • Source – Azaspiracids are produced by Azadinium and Amphidoma species.
   • Acute toxicity – It causes nausea, vomiting, stomach cramp and diarrhoea in man. In animals it causes fluid accumulation in intestine. Necrosis of intestinal villi, fatty liver change and damage of lymphoid tissue may occur.
   • Chronic toxicity – Repeated exposure causes inactivity and weight loss in animals. Interstitial pneumonia and shortening of intestinal villi may occur. Long exposure may also produce lung tumour and stomach epithelial hyperplasia in mice.
7. Ciguatoxins and Maitotoxin
   • Source – These toxins are produced by Gambierdiscus toxicus. They cause ciguatera fish poisoning.
   • Acute toxicity – It causes diarrhoea, vomiting and abdominal pain. Neurological symptoms appear after this. Weakness, tooth pain, metallic taste and pain on touching cold object may occur. Bradycardia and hypotension are also seen.
   • Chronic toxicity – Neurological symptoms may continue for months or years. Memory impairment, depression, chronic fatigue and generalized itching may remain for long time.
8. Palytoxins
   • Source – Palytoxins are produced by some Ostreopsis and Trichodesmium species.
   • Acute toxicity – It is very powerful toxin. It causes severe gastrointestinal distress and metallic taste. Rhabdomyolysis, acute renal failure, respiratory distress and cyanosis may occur. Death may occur rapidly due to cardiac arrest.
   • Chronic toxicity – Sublethal long exposure in animals causes blood biochemical change. Electrolyte imbalance, myocardial inflammation, lung inflammation and gastric ulcer may occur. Gas and mucus may accumulate in digestive tract.
9. Cyclic imines
   • Source – Cyclic imines include gymnodimines, spirolides and pinnatoxins.
   • Acute toxicity – In animal injection study it shows very fast toxicity. Neurological dysfunction, respiratory distress and death may occur within minutes. But oral toxicity is much lower.
   • Human toxicity – Definite human illness from seafood is not clearly proved. Skin contact with bloom water may cause acute dermatitis in swimmers.
   • Chronic toxicity – Chronic effect in man is not clearly established. Its importance is mainly due to fast neurological toxicity in experimental animals.

Control and Clinical Management of Algal Food Poisoning

A. Control and Prevention Strategies

• Monitoring of water and shellfish– Regular monitoring of sea water and shellfish is important. Water samples and bivalves are tested for algal toxins. Methods like LC-MS/MS and bioassay are used for detection of toxin.
• Early warning system– Early warning system is used during harmful algal bloom. When toxin level increases, the information is given to health authority and fishery department. This helps to prevent harvesting of toxic seafood.
• Public health advisory– Public warning is given in affected coastal area. People are advised not to collect or eat shellfish from bloom area. This is done during red tide and other harmful algal bloom.
• Closure of harvesting area– Affected fishery or shellfish harvesting area is closed temporarily. Collection of mussels, oysters, clams and scallops is stopped. The area is opened again only after toxin level becomes safe.
• Recall of contaminated food– Contaminated seafood is removed from market. Regulatory agencies may recall toxic shellfish, fish and blue-green algae supplements. This prevents further exposure to consumers.
• Use of safe seafood source– Seafood should be taken from approved and reliable source only. Unknown shellfish or self collected shellfish from bloom area should not be eaten. Dead or damaged shellfish should be discarded.
• Avoiding high risk parts– In large reef fishes, viscera may contain more toxin. Liver, intestine, roe, head and other internal parts should not be eaten. This is important in ciguatera fish poisoning.
• Proper storage of fish– Fish should be iced or refrigerated just after capture. This prevents bacterial change of histidine into histamine. This is important for prevention of scombroid poisoning.

B. Clinical Management Strategies

• Observation of patient– The patient should be kept under observation. Neurological sign, breathing, pulse and blood pressure are checked. Severe cases need hospital care and sometimes intensive care.
• Supportive treatment– There is no specific antidote for most algal food poisoning. So treatment is mainly supportive and symptomatic. The patient is observed and symptoms are managed.
• Fluid and electrolyte management– Vomiting and diarrhoea may cause dehydration. In this condition intravenous fluid is given. Electrolytes are also corrected according to the need of patient.
• Gastrointestinal decontamination– Activated charcoal may be given in early stage. It helps to reduce absorption of toxin from gut. It is useful only when much of the food is not already vomited out.
• Gastric lavage and cathartics– Gastric lavage is not always useful. Cathartics are also not routinely recommended. Their benefit is not proved in all algal toxin poisoning.
• Respiratory monitoring– In paralytic shellfish poisoning, respiratory failure may occur. So breathing should be watched carefully. If respiratory weakness develops, emergency support is needed.
• Ventilatory support– In severe paralysis, endotracheal intubation may be required. Mechanical ventilation is given when patient cannot breathe properly. This is life saving in severe saxitoxin poisoning.
• Treatment of bronchospasm– Inhaled brevetoxin may cause cough, wheezing and bronchoconstriction. Albuterol or other beta-adrenergic agonist is used. It is specially useful in asthma like attack.
• Treatment of neurological symptoms– In ciguatera and neurotoxic shellfish poisoning, severe neurological symptoms may occur. Intravenous mannitol may be used, mainly within 48 hours of onset. Chronic nerve pain may be treated with amitriptyline, gabapentin, pregabalin or fluoxetine.
• Treatment of cardiovascular effects– Bradycardia may occur in some poisoning. Atropine is used when bradycardia is symptomatic. Hypotension is treated by IV fluid, vasopressors or alpha-adrenergic drugs.
• Treatment of allergic like reaction– In scombroid poisoning, histamine like reaction occurs. It responds well to antihistamines. H1 and H2 receptor antagonists are used for treatment.

How to spot Toxic Algae?

• Change in water colour
  Toxic algae may change the colour of water. The water may look green, blue-green, brown or red. This type of bloom is commonly called red tide or brown tide.
• Scum on water surface
  The bloom may be seen as scum on the surface of water. It may look like dirty foam. Sometimes it looks like thick green layer floating on water.
• Paint like appearance
  Some toxic algal bloom looks like spilled paint. The colour may spread on the surface in patches. It may move with water current or wind.
• Thick mat formation
  Algae may form thick mat on the water surface. These mats may collect near shore, pond edge or slow moving water. It is common when water is warm and nutrient rich.
• Bad smell
  Water with harmful algal bloom may give bad smell. The smell may be rotten or foul. This occurs when algal mass starts decomposing.
• Foam formation
  Sometimes foam is formed near the shore. The foam may be coloured or dirty looking. It may contain algal toxin in bloom affected water.
• Not always visible
  All toxic algae cannot be seen easily. Some blooms remain below the water surface. So clear looking water may also contain toxin sometimes.
• Important point
  Toxic algae cannot be confirmed only by looking. If water colour is changed, scum is present or bad smell is found, then contact with water should be avoided. Shellfish and fish from that area should not be eaten.

Impact of Toxic Algae on Animals, Plants and Human

A. Impact on Human

• Food poisoning
  Toxic algae cause food poisoning in man. It occurs after eating contaminated shellfish and fishes. The important poisonings are PSP, ASP, DSP, NSP, ciguatera and clupeotoxism.
• Gastrointestinal effect
  It causes vomiting, diarrhoea and stomach cramp. Nausea and abdominal pain are also common. This occurs mostly after eating contaminated seafood.
• Nervous effect
  Some algal toxins affect nervous system. Numbness, tingling, weakness and loss of balance may occur. In severe case, memory loss, seizure, coma and paralysis may develop.
• Respiratory effect
  Some toxins come with sea spray and enter by breathing. Brevetoxin and palytoxin may cause cough, rhinorrhoea, wheezing and bronchoconstriction. Asthmatic person may get more problem.
• Skin and eye effect
  Contact with toxic bloom water may affect skin and eyes. Dermatitis, itching, hives and conjunctivitis may occur. Handling toxic coral may also cause corneal ulceration.
• Organ damage
  Microcystins affect liver and kidney. Long exposure may produce irreversible liver and kidney damage. It may also act as tumour promoter.

B. Impact on Animals

• Accumulation in shellfish
  Filter feeding shellfish collect algal toxins from water. Mussels, oysters, clams and scallops store toxin in their body. Usually shellfish may not show any disease.
• Food chain transfer
  The toxin passes from small organisms to larger animals. It may accumulate in crustaceans, gastropods, fishes and large predator fishes. This is called bioaccumulation.
• Poisoning of pets and livestock
  Pets and livestock may become ill after drinking bloom water. Dogs, cattle and other animals may die quickly. This is common in cyanobacterial bloom water.
• Death of aquatic animals
  Harmful algal bloom may kill fishes and other aquatic animals. Large number of animals may die at a time. This is referred to as mass mortality.
• Organ failure
  Marine toxins may damage liver, intestine, lung and heart of animals. Severe gastrointestinal erosion may occur. Respiratory failure and cardiac arrest may lead to death.

C. Impact on Plants and Aquatic Ecosystem

• Light reduction
  Dense algal bloom covers the water surface. Due to this, sunlight cannot enter properly into water. Aquatic plants and submerged vegetation get less light.
• Oxygen depletion
  After bloom death, decomposition takes place. During decomposition, dissolved oxygen is used up. This causes low oxygen condition in water.
• Dead zone formation
  When oxygen becomes very low, aquatic animals and plants cannot survive properly. Such area is called dead zone. It disturbs the whole aquatic ecosystem.
• Habitat damage
  Toxic algal bloom changes the normal condition of water. It affects aquatic plants, planktons and animals. Food chain and habitat balance are disturbed.
• Water quality loss
  Bloom makes water coloured, smelly and unhealthy. It reduces the quality of water for plants, animals and man. This also affects pond, lake and coastal ecosystem.

What Algal Toxins Tell About the Condition of Water

• Nutrient pollution
  Presence of algal toxin shows that water may have excess nutrients. Mainly nitrogen and phosphorus are more in such water. These nutrients come from fertilizers, sewage and runoff water.
• Eutrophication
  When nutrients become more, algal growth increases very fast. This condition is called eutrophication. Toxic bloom is an indication of polluted and nutrient rich water.
• Warm water
  Toxic algae grow better in warm water. So their presence may show high water temperature. Warm condition helps the bloom to form quickly.
• Slow moving water
  Toxic algal bloom is common in stagnant or slow moving water. In this type of water, algae remain collected in one place. This helps rapid multiplication of algae.
• Low oxygen condition
  Large algal bloom may reduce dissolved oxygen in water. After death of algae, decomposition uses oxygen. So the water may become oxygen poor.
• Dead zone
  Very low oxygen condition forms dead zone. In this area, fishes and other aquatic animals cannot live properly. Mass death of aquatic animals may occur.
• High sunlight
  Toxic bloom also shows that water is getting enough sunlight. Algae use sunlight for photosynthesis. With nutrients and warm condition, sunlight increases bloom formation.
• Poor water quality
  Algal toxin indicates that the water quality is not good. Such water may be unsafe for drinking, bathing, fishing and animal use. It may also be harmful for aquatic ecosystem.
• Damaged coral reef
  Presence of ciguatoxin may indicate damaged coral reef area. Toxin producing organisms grow more on dead or disturbed reef surface. Reef damage may occur due to acidification, construction and runoff.
• Environmental imbalance
  Algal toxin shows that the water ecosystem is disturbed. Nutrient load, warmth, slow water flow and low oxygen are usually connected with it. So toxic algae act as warning sign of bad water condition.

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