Harmful Algal Bloom

Algal Bloom Definition

An algal bloom is defined as the rapid growth or accumulation of algae in aquatic ecosystems. Harmful algal blooms (HAB) are algal blooms composed of phytoplankton known to naturally produce bio-toxins that are harmful to the resident population as well as humans. The presence of harmful algal blooms lead to fish die-offs, fish sickness, and human sickness when affected organisms are consumed.

Causes of Algal Blooms

Algal blooms are caused by excessive amounts of nitrates, phosphates, and nutrients entering an aquatic ecosystem, often by discharges of sewage treatment plants, septic tanks, and storm water run-off from fertilized lawns and farms. Other factors that aid algal growth include sunlight and slow-moving water.

These nutrients cause a type of pollution called eutrophication. Eutrophication entails excess nutrients stimulating an explosive growth of algae. As these algae grow, out-competed plants die off and become food for the bacteria that decompose them. With more food available now, the bacteria also experience an explosive growth, rapidly using up all the oxygen in the water until many fish and aquatic insects can no longer survive. The end result of an algal bloom is a dead zone.

Algal Bloom Effects

The detrimental effects of harmful algal blooms can vary from cell and tissue damage, to organism death. These effects can be caused by varying mechanisms including toxin production, predation, particle irritation, induced starvation, and localized anoxic conditions. The results are devastating not just for the resident aquatic populations, but also to many other plants and animals in the community – including people. In humans, direct exposure to toxins via drinking water can cause a series of health issues such as rashes, stomach or liver illness, respiratory problems, and neurological effects.

Toxins

A few of the harmful algal bloom species are known to naturally produce biotoxins that are poisonous to aquatic organisms and humans. Pfiesteria piscicida, to name one, is known to produce dermonecrotic and neurologic toxins that impacts fish and humans. Cyanobacteria, to name another, is also known to produce neurotoxins and hepatoxins.

These toxins can cause a range of symptoms in affected organisms including vomiting, diarrhea, loss of appetite, seizures, convulsions, paralysis, increased heart rate, excessive tiredness, and difficulty breathing.

Predation

Some harmful algal bloom bacteria are, in a sense, predators of the resident fish population. Their neurotoxins and dermanecrotic toxins assist in predation by killing the neurosystems and the skin of the affected fish. These toxic components can cause lesions to form in the fish’s skins, leading to a sloughing off of skin layers and to infection. When the fish die, their organic compounds become food for the bacteria that killed it.

Particle Irritation

Other harmful algal bloom species, such as the spine-forming diatoms, get stuck in the gills of animals. The result is an accumulation of mucus and respiratory failure, as well as internal bleeding and bacterial infection. People often get sick from eating shellfish containing toxins produced by these algae.

Induced Starvation

Harmful algal bloom species can starve animals to death through nutritional and size mismatch. Basically, animals that feed on the harmful algal bloom species don’t get enough nutrition despite eating large quantities. The result is nutritional deprivation and, ultimately, death. Other harmful algal bloom species reduce the appetites of affected animals, leading to death by starvation.

Localized Anoxic Conditions

Excessive algae growth and the subsequent death of out-competed plants leads to increased numbers of decomposing bacteria. With an abundant food supply of dead organic material, the newly enlarged bacteria population use up all the oxygen in the water, causing hypoxic and anoxic conditions. The result is a mass mortality of fish and shellfish. The area becomes a dead zone, unable to sustain life.

Quiz

1. What causes anoxic conditions during a harmful algal bloom?
A. The algae itself.
B. The plankton in the algae.
C. The bacteria that decompose dead organic material.
D. The overpopulation of fish.

Answer to Question #1

C is correct. When the bacteria decompose the dead organic material, they use up all the oxygen in the process.

2. What does NOT contribute to the growth of harmful algal blooms?
A. Sunlight
B. Slow moving water
C. Nutrients
D. Humidity

Answer to Question #2

D is correct. Humidity is not related to the growth of harmful algal blooms. Sunlight (heat), slow moving water, and nutrients feed to growth of harmful algal blooms.

3. What term describes: “an excessive richness of nutrients in a body of water causing a dense growth of plant life and death of animal life from lack of oxygen”?
A. Eutrophication
B. Harmful algal bloom
C. Biotoxins
D. Anoxia

Answer to Question #3

A is correct. A harmful algal bloom is the rapid growth or accumulation of algae. Biotoxins are a product of the harmful algal bloom species. Anoxia is the absence of oxygen. The phrase in the question best defines the term eutrophication.

References

• The Effects: Human Health. (2017, March 10). Retrieved June 04, 2017, from https://www.epa.gov/nutrientpollution/effects-human-health


• Algal bloom. (2017, May 31). Retrieved June 04, 2017, from https://en.wikipedia.org/wiki/Algal_bloom


• Harmful Algal Blooms. (n.d.). Retrieved from http://oceanservice.noaa.gov/websites/retiredsites/sotc_pdf/hab.pdf


• Harmful Algal Blooms (HABs) FAQs. (n.d.). Retrieved June 04, 2017, from http://www.dec.ny.gov/chemical/91570.html

Harmful Algal Bloom