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Effects of Algal Toxins

Updated on May 29, 2015
Harmful marine algae
Harmful marine algae | Source

Are you aware of the possible algal toxins you may have in your pond or in your area’s surrounding bodies of freshwater? Algal toxins are considered problems in freshwater bodies of water, where shellfish and fish live. Invertebrates and vertebrates can both suffer from algal toxins and this usually results in direct toxicity, off flavor, and alterations in water quality.

Algal toxins are known to be molecules, made by different types of freshwater, marine, and brackish species of algae. They can also be found in wet soil. If the factors are favorable enough for them to accumulate in right quantities, they can cause problems to the surrounding aquaculture. Algal toxins can decrease growth rates, reduce feeding rates, kill cultured organisms, and cause issues in food safety.

Algal blooms or dense algal accumulations are usually the known causes of algal toxins. Harmful Algal Blooms (HAB) describes the advanced proliferation of phytoplankton or algae. When severe blooms appear (non-toxic algae included), it is sure disaster. This event affects the health and well-being of cultured animals. The reason is that the algae deplete the amount of dissolved oxygen in the water—a process also known as eutrophication. Some large algal blooms often change the color of the water. This becomes known as brown tide or red tide. The discoloration is often undetectable until the algal bloom has completely taken over.

Algal bloom
Algal bloom | Source

Effects of HAB

HAB (Harmful Algal Blooms) is a serious problem. The blooms can affect the surrounding ecosystems and general public health. Here are some of the known detrimental effects:

  • Algal toxins are incorporated into the food chain through their accumulation in filter feeders, such as scallops, clams, oysters, and mussels. These organisms eat the toxic phytoplankton.
  • The mammals, birds, and fish that eat the contaminated filter feeders die.
  • The structure and function of aquatic ecosystems (freshwater or marine) are changed significantly.
  • The water becomes unsightly.
  • The dissolved oxygen is depleted because of the decaying biomass.
  • The important species of algae in the food web are killed off.

Cyanobaceria bloom
Cyanobaceria bloom | Source

Most Common Toxin-Producing Marine and Freshwater Algae

The following are known algae that produce algal toxins:

1. Cyanobacteria

Also known as, blue-green algae, cyanobacteria live in marine, hypersaline, brackish, and freshwater environments from the hot springs to the icy waters of the arctic. They can also inhabit land environments. Some cyanobacteria can reduce N2 to NH3, and then into proteins and amino acids. They reproduce by the process of binary fission. They also have murien in the cell wall. With these features, they are physiologically and structurally similar to gram-negative bacteria. Yet, they make their own food through the process of photosynthesis. Cyanobacteria can directly affect zooplankton and fish production because of the toxins (hepatotoxins and neurotoxins) they produce. They also give way to allelochemicals, which block competing invertebrate grazers and algae. The toxins produced by cyanobacteria can be classified based on their chemical structures:

  • Alkaloids
  • Lipopolysaccharides
  • Peptides

The cyanotoxins are also discussed by their animal toxicity:

  • Dermatotoxins (by benthic cyanobacteria)
  • Neurotoxins (by Oscillatoria and Anabaena)
  • Hepatotoxins

2. Pymnesiophytes

Also known as, golden brown algae, pymnesiophytes are made up of toxic algae species that form detrimental blooms in brackish water. They are relatively small, halophilic organisms produce ichthyotoxin, which brings about fish kills extensively. They make the fish lose their selective permeability. This makes them vulnerable to toxins. Affected fish have bloody gills, scales, and fins. They are also covered in mucus. If you remove these fish into uncontaminated water, they will be able to recover after a few hours. Golden alga does not harm humans, yet the affected fish should not be eaten.

3. Euglenoids

Euglenoids produce ichthyotoxin in fresh bodies of water. Once the Euglena toxins are ingested, the fish begin to stop eating, become disoriented, swim near the surface, swim upside down, or swim to their sides. The fish dies within a day. The gills also redden upon death.

Blue-green algae
Blue-green algae | Source

Algal Blooms

Periodic algal blooms such as those brought about by cyanobacteria or dinoflagellates, have affected freshwater and saltwater environments all over the world. Some species of algae kill wildlife, humans, shellfish, livestock, and fish. Cyanobacterial blooms start as green and then become blue. They sometimes turn into scum in the water. Some of the toxins are saxitoxin (PSP or paralytic shellfish poisoning toxin), cyanobacterial toxins, domoic acid, and brevetoxin. Those that have nodularin or microcystins cause liver damage.

Detrimental Marine Algae

Marine algal species, detrimental to marine animals are those that build up in shellfish. In the United States, NSP (neurotoxic shellfish poisoning) is a result of eating shellfish, contaminated by an algal toxin known as brevetoxins from Karenia brevis. This species of algae is found in the waters of Florida. Symptoms include chest tightness, sore throat, and eye irritation. These symptoms may last for days after exposure to the algae. Another type of poisoning from harmful marine algae is Ciguatera tides fish poisoning, which is caused by ciguatoxin. This toxin may accumulate in large quantities in large reef fish.

Red tide bloom
Red tide bloom | Source

Red Tide Blooms

Karenia brevis is a species of algae, which grows quickly. It creates brown or red blooms. The blooms are known as red tide. This species produces brevetoxins, which kills off marine organisms. Red tide blooms damage shoreline quality, local businesses, and the general fishing industry. It is difficult to pinpoint a possible red tide bloom because the organism’s movement depends on the tides and the winds.

People who eat shellfish, infected by Karenia brevis suffer from neurotoxic food poisoning. This type of poisoning brings about tingling fingers or toes and gastrointestinal symptoms. Even breathing the air near a red tide contaminated body of water or swimming in red tide blooms, may affect human health.

Ciguatera | Source

Ciguatera Species

Ciguatera is a type of fish poisoning caused by eating fish, containing toxins from Gambierdiscus toxicus. Species of fish, which are often affected by this type of algae, are:

  • Horse-eye jack
  • King mackerel
  • Barracuda
  • Blackfin snapper
  • Black grouper
  • Dog snapper
  • Cubera snapper
  • Yellowfin grouper
  • Hogfish
  • Greater amberjack

Symptoms of this type of poisoning are tingling of the toes or fingers, vomiting, and nausea. Affected people may also feel hot things as cold and may feel cold things as hot. Ciguatera usually goes away after days or even weeks. It has no cure. The symptoms can be treated.

Remember that algae are important in balancing out freshwater and marine ecosystems. Most of them are beneficial. Natural sources of drinking water also contain algal blooms. They have microscopic species of algae that proliferate quickly. They do so because they respond to the altered changes in the water’s chemicals (phosphorous and nitrogen). Too much algae in the water can deplete the dissolved oxygen in the water. They can also block the sunlight, which discontinues the process of photosynthesis in aquatic plants.

Be aware of the harmful species of algae and the toxins they produce. Ask for the help of your pond expert, so that you can have a safe body of water within your property. If you do your homework, you can stay away from contaminated beaches and lakes.

Harmful Algal Blooms


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