HABs Information

Marine algae range from microscopic single celled organisms (phytoplankton) to larger mulitcellular seaweeds like kelp. As photosynthesizers, harvesting energy from sun to produce their own food, algae are the base in many marine food webs and are therefore immensely important to the functioning of our planet.

A harmful algal bloom (HAB) causes negative impacts to ecosystems or organisms through the production of natural biotoxins by certain kinds of microscopic algae (e.g. phytoplankton), physical damage to fish gills, or through discoloration of the water. Marine biotoxins are normally present in amounts too small to be harmful. However, a combination of warm temperatures, sunlight, and nutrient-rich waters can cause rapid plankton reproduction, or "blooms." These blooms are commonly referred to as harmful algal blooms or "HABs" because of their potential to cause large-scale marine mammal or bird mortalities and have been associated with human deaths.

These are some of the common harmful algae found in the Pacific Northwest:


  • A pennate diatom that can produce the toxin domoic acid.
  • Domoic acid poisoning in humans known as amnesic shellfish poisoning (ASP).
  • ASP can cause temporary and permanent short-term memory loss.


  • A dinoflagellate known for the suite of toxins that it produces referred to as paralytic shellfish toxins (PST).
  • PSTs are responsible for the human illness called paralytic shellfish poisoning (PSP).
  • PSP can cause tingling of the lips, tongue, short term paralysis and even death.


  • A dinoflagellate, some species of which are known to produce toxins such as okadaic acid and dinophysistoxins.
  • Toxins from dinophysis are responsible for the human syndrome called diarrheic shellfish poisoning (DSP). The first DSP event in the USA occurred in Sequim Bay in 2011.
  • DSP shellfish poisoning includes symptoms such as diarrhea, nausea, vomiting, and abdominal cramping.


  • A small flagellate that is known to produce the toxins called azaspiracids. This organism has recently been identified in Puget Sound.
  • The syndrome in humans is called azaspiracid poisoning (AZP). AZP was first reports in the Netherlands in 1995.
  • Symptoms of AZP are chills, headaches, diarrhea, nausea, vomiting and stomach cramps.


  • A raphidophyte that produces an uncharacterized toxin or toxins. This is the major fish-killing organism in Puget Sound.
  • Cells can cause irritation of the gills, creating excess mucus and thereby preventing fish from taking up oxygen from the water.

Is Shellfish Safe?

Additional Resources


Olympic Region Harmful Algal Blooms

SoundToxins Partnership

Washington Dept. of Health Marine Biotoxins Overview

2015 Toxic Algae Bloom Might be Largest Ever

Marine Toxins Stop Northwest Shellfish Harvesting

Deadly Plankton Invasion Takes Toll on Fish