Summary
Toxin-producing algae multiply in nutrient-rich water, poisoning shellfish and marine life.
In depth
Dinoflagellates such as Karenia brevis cause red tides; toxins (saxitoxin, domoic acid) accumulate in shellfish causing paralytic or amnesic shellfish poisoning. Drivers include nutrients and warming. Monitoring closes fisheries.
Toxins can biomagnify and affect marine mammals and humans. Monitoring uses satellite imagery and shellfish testing.
Key idea: excess nutrients, warmth and stratification promote blooms.
Harmful algal blooms (HABs) are rapid growths of algae or cyanobacteria that produce toxins or harm ecosystems by sheer biomass. They are fuelled by nutrient pollution, warm water, calm stratified conditions and sometimes upwelling.
Toxins such as saxitoxin (paralytic shellfish poisoning), domoic acid (amnesic poisoning) and brevetoxin accumulate in shellfish and fish, harming people, marine mammals and birds. Red tides from dinoflagellates such as Karenia brevis kill fish. Freshwater cyanobacterial blooms release microcystin. Decomposing blooms also use up oxygen.
Example: Lake Erie blooms contaminated Toledo's drinking water in 2014.
Key idea: reducing fertiliser and sewage nutrients is the best long-term remedy; climate change is expected to worsen blooms.
Frequently asked questions
What is Harmful Algal Blooms?
Toxin-producing algae multiply in nutrient-rich water, poisoning shellfish and marine life.
Which area of biology covers Harmful Algal Blooms, and how advanced is it?
Harmful Algal Blooms is one of the 54 topics in Marine & Environmental Biology. It is rated Advanced, so it suits learners who want specialist depth. Related topics in this area include Dead Zones, Upwelling, Plankton.
Can you give an example of Harmful Algal Blooms?
Manatees and fish die in Florida red tides.
What should I learn before Harmful Algal Blooms?
Work through the Beginner topics in Marine & Environmental Biology first, such as Oceans, Ocean Zones, Plankton, then return to Harmful Algal Blooms. Advanced topics assume the Intermediate vocabulary.
What topics are related to Harmful Algal Blooms?
The closest topics to Harmful Algal Blooms are Dead Zones, Upwelling, Plankton, One Health. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Harmful Algal Blooms?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Harmful Algal Blooms. To practise the whole of Marine & Environmental Biology, use the Marine & Environmental Biology quiz.
How is Harmful Algal Blooms different from Dead Zones?
Harmful Algal Blooms: Toxin-producing algae multiply in nutrient-rich water, poisoning shellfish and marine life. Dead Zones: Oxygen-depleted ocean areas caused by nutrient runoff, fertiliser and decomposition of algal blooms. Read both side by side and note what each one explains.
How should I study Harmful Algal Blooms step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Dead Zones and explain the difference aloud. Finally, take the Marine & Environmental Biology quiz and come back to this page for any question you miss.