What’s driving toxic algae blooms that are poisoning CA animals?

Written by Amy Ta, produced by Andrea Bautista

The coast is foggy in Central California, where hundreds of sea lions and dolphins have died this month likely due to toxic algae. Credit: Shutterstock.

During the first weeks of June, hundreds of sea lions and dolphins off the coast between Santa Barbara and San Luis Obispo have died — likely due to toxic algae called “red tide.” Rescuers of the beached and sick animals say it’s one of the worst mass poisoning events they’ve seen. The bloom is even spreading south to Los Angeles and San Diego. 

Patrick Krug, a marine biologist at California State University, Los Angeles, says this is an amplified version of a natural cycle that happens during summer. 

“This is when we would normally have blooms of microalgae that form the base of the food web or our coast. And that's because we get a combination of upwelling that brings nutrients to the surface and longer daylight. So like any plant, algae thrives when there's sunlight and nutrients,” he explains. “But sometimes, probably with increasing frequency because of human perturbations to the system, we're getting these extreme blooms with more frequent and devastating consequences, where these single cells can reach densities of 10 million per liter. And sometimes they will switch to the production of toxins that get amplified as they accumulate up through the food chain.”

He says the algae is now producing a powerful neurotoxin that attacks the nervous system of animals higher up in the food chain, particularly dolphins and sea lions. 

Humans could be affected too, he adds. That’s if they eat contaminated shellfish, such as mussels, clams, and crabs. The poisoning could lead to short-term memory loss, and comas and deaths in extreme cases. Thus, public health warnings are in place, especially in Central California. 

How is human activity exacerbating the blooms? Agriculture, Krug identifies. “As we fertilize farms, a lot of those excess nutrients wash into the coastal oceans. And they do the same thing — they fertilize algal blooms. … There's a global link between increased algal blooms and increased reliance on modern agricultural methods to sustain food security.”

He points out that climate change could be a contributing factor too, since some strains do better in warmer water. 

“All of these things combined may be leading to more of these extreme algal bloom events.” 

Fortunately, sick dolphins and sea lions can recover. Volunteers with the group Channel Islands Marine and Wildlife Institute are trained to rescue the wildlife in response to calls from the public. If they can reach the animals in time, they give them rehydration and anti-nausea medications, and feed them toxin-free fish.



  • Patrick Krug - marine biologist at California State University, Los Angeles