What are harmful algal blooms?
Algae – microscopic, single-celled plants – that live in the ocean sometimes “bloom” or multiply so quickly that they appear in dense patches on the sea’s surface. Although most are harmless, some species produce toxins that move up through the food web and can kill shellfish, fish, birds, marine mammals and even humans.

Why is domoic acid such a concern?
Occasionally along the California coast the diatom Pseudonitzschiablooms and produces a neurotoxin called domoic acid. No one knows what sets off the glass-shelled algae to bloom or produce so much domoic acid. This toxin can cause seizures and even death in otters who eat contaminated shellfish. Many otters develop inflammation of heart muscle and heart failure after being exposed to domoic acid. Heart disease is responsible for 13% of sea otter deaths. 

Is domoic acid dangerous to people?
Humans who eat shellfish or fish tainted with domoic acid can start twitching and feel nauseous. The toxin can permanently destroy a part of the brain that controls short-term memory and, in severe cases, causes death.