Impact of Climate Change on Water-borne Diseases and Toxic Algae

Toxic algae: types and climate change effects.

Harmful algal blooms (HABs) are the rapid growth of algae or cyanobacteria that can cause harm to people, animals, or the local ecology. Harmful algae or cyanobacteria can look like foam, scum, paint, or mats on the surface of water and can be different colors. These blooms can produce toxins that make people and animals sick. Blooms occur in fresh water, such as lakes and rivers, and salt water, such as oceans or bays. Algae and cyanobacteria are simple organisms that live in the water. Algae and cyanobacteria can rapidly grow out of control, or “bloom,” when water is warm, slow-moving, and full of nutrients.

In fresh water, such as lakes and ponds, harmful blooms are most commonly caused by cyanobacteria (also called blue-green algae), which are a kind of single-celled organism called phytoplankton. Some cyanobacteria produce toxins (poisons) called cyanotoxins. When people or animals are exposed to cyanotoxins, they can become sick. People exposed to cyanotoxins by touching or swimming in contaminated water or breathing in droplets of contaminated air, eating contaminated food or dietary supplements, or by swallowing contaminated water, may experience the following symptoms, depending on the cyanotoxin involved:

Ø Irritation of the eyes, nose, skin, throat, or lungs

Ø Stomach pain

Ø Headache

Ø Neurological symptoms (for example, muscle weakness, dizziness)

Ø Vomiting

Ø Diarrhea

Ø Liver damage

In salt water, such as oceans and bays, harmful algal blooms are most commonly caused by diatoms and dinoflagellates, which are two kinds of phytoplankton (single-celled organisms). Some diatoms and dinoflagellates can produce toxins (poisons). When people or animals are exposed to these toxins, they can become sick. People are exposed to marine algal toxins through: eating shellfish or fish containing toxins; swimming or other activities in the water; breathing in tiny droplets in the air that contain toxins. Types of illness that can be caused by eating seafood contaminated with toxins from harmful algae:

Ø Ciguatera Fish Poisoning (CFP)

Ø Neurotoxic Shellfish Poisoning (NSP)

Ø Paralytic Shellfish Poisoning (PSP)

Ø Domoic Acid Poisoning and Amnesiac Shellfish Poisoning (ASP)

Ø Diarrheic Shellfish Poisoning (DSP)

Ø Azaspiracid Shellfish Poisoning (AZP)

These illnesses can produce severe symptoms including vomiting, diarrhoea, dizziness, respiratory problems, paralysis or, in extreme cases, even death.

Climate change impacts that might affect exacerbate algal blooms:

Ø Warming water temperature. Toxic algae prefer warmer water. Prevents water from mixing – algae grow thicker and faster. Small organisms move easier – floating to the surface faster. Algal blooms absorb sunlight – acceleration (even warmer water, promoting blooms).

Ø Changes in salinity. Saltier freshwater – invasion of marine algae.

Ø Higher CO₂ levels.

Ø Changes in rainfall. Alternating periods of drought and intense storms – nutrient runoff into waterbodies.

Ø Coastal upwelling. Excess nutrients from the sea floor.