Science Spotlight: Domoic Acid

by Devika G. Bansal

In August 1961, in the middle of the night, a massive flock of sooty shearwaters crashed into homes in Santa Cruz County in a mysterious frenzy, terrifying homeowners and puzzling officials. The event inspired then-local resident Alfred Hitchcock, who made his film The Birds two years later.

The incident remained a mystery until 2012, when scientists from the Scripps Institute concluded that the frenzy and subsequent die-off was caused by a floating ocean colony of tiny needle-shaped algae, which churn out a toxin called domoic acid. The toxin poses health risks to animals and humans alike.

A potent neurotoxin, domoic acid comes from Pseudo-nitzschia, a genus of diatoms found along the Pacific coast. These exquisite single-celled algae build walls of shimmering opal. Domoic acid helps the algae survive by capturing iron, a necessary nutrient, from seawater.

Diatoms grow in “bloom and bust” cycles each year. Warmer waters and bigger algal blooms mean more toxins. “We know temperature plays a role in how big the blooms get,” says toxicologist Kathi Lefebvre of the Northwest Fisheries Science Center in Seattle. Researchers don’t yet know what triggers algae to pump out more domoic acid, but coastal pollution and fertilizer runoff from farm fields may inflame the blooms.

As the Pacific heats up, more potent blooms may lie ahead. Scientists recorded the largest and longest-lasting algal bloom in 2015, stretching from Central California to northern Washington. The outbreak forced regulators to close the popular Dungeness crab fishery for months.

Domoic acid poisons the central nervous system of seabirds, marine mammals and humans. At high levels, it can cause seizures, disorientation and memory loss. Fish and shellfish can build up domoic acid in their gut—making them dangerous carriers as they pass the toxin up the food chain.

The news is not all grim: blooms cannot poison swimmers and surfers, Lefebvre says. “Even if you were to drink a liter of seawater, there would never be enough toxins to cause problems,” she says. “You would have more problems with the seawater you drink.”

Follow this link to read more about the science behind 'The Birds'.

Note from the editors: Science Spotlights are a joint project of the UCSC Science Communication Program and Hilltromper. This article was published in February 2017.