4.4E Algal blooms and anoxic/hypoxic waters (HL) Notes

1. Harmful algal blooms (HABs) occur when cyanobacteria, protists, algae, or dinoflagellates proliferate excessively in aquatic ecosystems, often due to nutrient pollution (eutrophication), climate change, or water stagnation.
2. Some HABs release toxins harmful to humans, fish, and other animals, leading to neurotoxic, hepatotoxic, or paralytic effects.

Organisms Involved in HABs

1. Cyanobacteria (blue-green algae): dominant in freshwater.
2. Dinoflagellates: common in marine environments and estuaries.
3. Protists and other algae: diverse eukaryotic organisms that thrive in nutrient-rich water.

Causes of Harmful Algal Blooms

1. Eutrophication: excess nitrates and phosphates promote algal growth.
2. Rising temperatures: warmer waters accelerate algae reproduction.
3. Stratification: prevents oxygen mixing, creating stagnant conditions.
4. Sewage and agricultural runoff: major nutrient inputs.
5. Light and calm waters: favour photosynthetic growth and bloom persistence.

Freshwater Example - Cyanobacterial Blooms

Cyanobacteria and Cyanotoxins

1. Common genera: Microcystis, Anabaena, Nostoc, Cylindrospermopsis.
2. Thrive in nutrient-rich, warm, and stagnant waters.
3. Produce cyanotoxins such as:
   1. Microcystins: damage liver tissue.
   2. Anatoxins: affect nervous system.
   3. Cylindrospermopsin: causes liver and kidney damage.
4. Exposure pathways:
   1. Drinking contaminated water.
   2. Skin contact during recreation (swimming).
   3. Inhalation of aerosolized toxins near blooms.
   4. Consumption of contaminated fish or shellfish.
5. Effects on humans:
   1. Skin irritation, eye inflammation, nausea, vomiting.
   2. Chronic exposure may lead to liver disease or neurological symptoms.
6. Effects on animals:
   1. Domestic animals and livestock can die after drinking contaminated water.
   2. Fish die-offs due to oxygen depletion and toxin ingestion.

Marine Example - Dinoflagellates

1. Organisms: Karenia brevis, Alexandrium spp., and Gambierdiscus toxicus.
2. Toxin Type: Neurotoxins, paralytic, amnesic, and diarrhetic shellfish poisons.
3. Visual Appearance: “Red tides”, discolored water (red, brown, or orange) caused by dense dinoflagellate blooms.
4. Transmission:
   1. Bioaccumulation in shellfish (e.g., mussels, clams, oysters).
   2. Humans affected by eating contaminated seafood.
5. Human Illnesses:
   1. Paralytic Shellfish Poisoning (PSP): muscle paralysis due to saxitoxins.
   2. Neurotoxic Shellfish Poisoning (NSP): nausea, dizziness, and neurological effects.
   3. Amnesic Shellfish Poisoning (ASP): short-term memory loss due to domoic acid.