Toxic Algae Bloom Forces Fisheries to Shut Down

See our 4-minute California Matters segment on oysters and ocean acidification here.

Earlier this month, the California Department of Public Health issued a warning regarding the toxins found in seafood from Monterey and Santa Cruz. This was due to a large bloom of algae, forcing them to shut down fisheries in the area. However, the toxins are not only affecting California. There have been closings in Oregon and Washington, and the bloom may even stretch into British Columbia and Alaska. When all is said and done, this may be the largest toxic algae bloom ever recorded.

But what does this mean for consumers of California seafood? I spoke to Raphael Kudela, professor of ocean sciences at UC Santa Cruz, about the bloom.

Can you describe what this algae bloom is?

Raphael Kudela: It's a bloom caused by a diatom called Pseudo-nitzschia. This organism is pretty much always around here, it shows up pretty much everywhere in the ocean. But under the right conditions, it produces the toxin "domoic acid," and that gets into the food system. If you consume enough of it, it gets into your brain, and causes damage to your short term memory capability. If you keep increasing the concentration, it can actually kill you. It was first discovered in 1991, in Prince Edward Island mussels, and several people have died from it. Fortunately, once we realized it was there, we haven't had any deaths we know of in the U.S.

Who is affected by this bloom?

Kudela: When it blooms the way it is right now in California, its primary impact is to wildlife. The commercial shellfish fisheries tend to be shut down. They shut down the anchovy fisheries in Monterey and Santa Cruz counties because the anchovies are also very toxic. So, it's been kind of an interesting summer. The blooms are oftentimes around this time of year, but this particularly bloom is the largest one both in terms of area and the toxicity in about 15 years. It's a particularly big toxic bloom we're seeing this year.

Is there a reason why this one is so big?

Kudela: Nobody knows for sure. These blooms tend to be more toxic and bigger when we have El Niño conditions, where warmer water upswells, altering between a little bit of cold water coming up with the northwest winds, and going back to warm conditions. That's exactly the conditions this particularly algae grows well in. But also, last year and this year there's been this phenomenon they've coined "the warm blob," where warm water that has been sitting out in the Pacific has pushed its way onto the coast.

How much seafood does someone need to eat in order to get sick?

Kudela: The number we use is 100 grams of shellfish or fish, so you're talking about a quarter pound. When we get to 20 parts per million, there's the potential you would get sick or queasy. That's pretty protective. To give you an idea of where we are, a couple weeks ago the shellfish here at Santa Cruz were about 80 parts per million, or four times higher. At that level, eating a restaurant dish of mussels would almost certainly make you sick. The anchovies -- which, people aren't generally eating anchovies, but that's how it gets into the food system -- they're up at 100 to 400 parts per million, so very toxic. It wouldn't take even a full serving and you'd be pretty violently ill.

What are the symptoms?

Kudela: They are similar to food poisoning. Nausea, maybe a little dizzy, probably vomiting. As you keep increasing the toxicity, the symptoms get worse. So more nausea, vomiting, difficulty balancing. And if you keep going beyond that, that's when it starts to impact your brain. You're not necessarily aware of your surroundings, and you're having memory impairment. Fortunately, we haven't seen that in humans in the last 20 years. But where we do see that progression of symptoms is in organisms. California sea lions are a good example. If you see them stranded on the beach and waving at their head and scratching behind their ears, they've gotten too many toxins.

Is this something consumers need to be worried about?

Kudela: It's mostly a wildlife problem. Obviously, the sea lions and pelicans don't read the signs, so they're being exposed toxins because it's in the fish they're eating. The California Department of Public Health is really proactive with monitoring this. Same with other states. As soon as those levels get anywhere close to a point where it could cause problems for humans, they start shutting down the fisheries. So, it's perfectly fine to go to a restaurant. It's perfectly fine to buy seafood, because it's rigorously tested. The only time you would find yourself in trouble is if you're ignoring the signs and going out and getting your own anchovies and shellfish.