Climate Change

On the Enigmatic ‘Flying Potato,’ Neither Plant Nor Animal, That Caused the Bay’s Biggest Harmful Algal Bloom in History

How will we know when the next one is coming?

September 21, 2022

At times this summer, the shores of San Francisco Bay looked like a piscine battlefront — strewn with dead white and green sturgeon, leopard sharks, striped bass, bat rays, smelt, anchovies, and other fish. It started in late July in Alameda and expanded throughout the entire Bay. By late August, some 10,000 fish had reportedly died at Oakland’s Lake Merritt alone. Where the killer algae bloomed, the water was dull and rust-colored. One resident was quoted saying “the end was near”. A local scientist called the event a “wildfire in the water”. The murk came from the sheer density of the culprit, which was multiplying in the millions: a miniscule organism called Heterosigma akashiwoakashiwo means “red tide” in Japanese. This wasn’t H. akashiwo’s first star turn. 

H. akashiwo had caused huge, awful blooms in Japan (where it was first described in 1967) and in the Pacific Northwest, where in the mid-1990s and 2000s it killed so many farmed and wild fish that each bloom cost some $2 million to $6 million. Here in the Bay, it had been a relatively chill regular in the phytoplankton crew for years without acting out, showing up in 65 percent of the regular water samples in the central Bay. In California, it wasn’t even considered harmful enough to really worry about, because it wasn’t making toxins that would bioaccumulate in the food chain. But now that H. akashiwo has managed to cause the biggest harmful algal bloom in the Bay’s history, scientists are scrambling to learn more.

“That’s the million dollar question for people that study phytoplankton — why now, and why this organism?” Raphael Kudela, ocean science professor at the University of California, Santa Cruz, says. “It’s like the lottery. There’s all these players in the background. And sometimes they’ll pop up and take over.” 

A grid of twelve computer-generated images of the Bay, from Aug. 3, 2022, to Sept. 9, 2022. The water's color corresponds to the extent of chlorophyll growth in the bay (which is measured via fluorescence, by satellites). By late August, the whole Bay is filled with algae. (National Oceanic and Atmospheric Administration)
And take over it did. In this time series of images from early August to early September, red indicates where the chlorophyll levels were the highest — aka where the algae was blooming. By late August, the entire Bay was filled. (National Oceanic and Atmospheric Administration)

Harmful algal blooms, or HABs, happen when microscopic marine algae called phytoplankton encounter just the right conditions to go nuts and start reproducing very rapidly, reaching concentrations of millions of cells per gallon of water. Sometimes, the cells begin to produce toxins. A bloom can be benign, but it gets into HAB territory when it starts killing things or making people or animals sick. Often that’s the toxins at work, but sometimes it’s just because the bloom hogs all the oxygen that other creatures need. HABs are as varied as colors of the rainbow, or more precisely the many species of phytoplankton. Most commonly, you hear about the dinoflagellates and diatoms that have been higher priority — like Alexandrium catenella, the dinoflagellate that causes paralytic shellfish poisoning, or the diatom Pseudo-nitzschia australis, whose neurotoxin, domoic acid, shut the Dungeness crab fishery down in 2015.

But H. akashiwo is from a third class — the raphidophytes, which are protists. This single-celled alga, which looks like nothing more than a cornflake under a microscope, can photosynthesize like a plant, and move about on two hairlike flagella, like an animal. It’s neither plant nor animal nor fungus. And to scientists, it’s still rather mysterious. The key unanswered questions are what conditions trigger it to bloom, and why it sometimes turns toxic, or doesn’t. 

But before you can unpack the ecosystem questions, you have to understand the organism itself. And H. akashiwo isn’t easy to get a handle on. First, it’s literally squishy, lacking a rigid cell wall, which makes it somewhat fragile to collect. Try and preserve it with chemicals, and they deform or burst its delicate cells. And being quite a cosmopolitan, well-traveled alga, it changes its looks ever so slightly wherever it goes — so it’s a little different in, say, Japan, compared to San Francisco Bay, making it harder to identify. 

A lot of what we know about H. akashiwo is thanks in part to scientists who worked for three years, starting in 2010, in a tricked-out shipping container parked by the waters of San Juan Island, in Washington. This was referred to, by the National Oceanic and Atmospheric Administration, which ran it, as a “living laboratory.” There, scientists could isolate samples of the evanescent, finicky algae, and incubate them outdoors in conditions like the ones where they naturally flourished. The impetus to do this was both scientific and monetary — since the mid-1990s, H. akashiwo blooms had begun to pop up, with little warning, all over the inland waters of the Pacific Northwest and southwestern British Columbia.

One of the people in that container lab was William Cochlan, a research professor and senior research scientist at San Francisco State University’s Estuary and Ocean Science Center. Cochlan is one of few California experts on H. akashiwo, which his graduate students at the time, Cochlan recalled, nicknamed the “flying potato.” Later, he thought, “No one knows anything about the physiology of these cells. No one grows or studies them on the West Coast — I’m going to start doing this.”  

The ‘flying potato,’ Heterosigma akashiwo. (Courtesy of William Cochlan)

This is how Cochlan’s ecophysiology lab, which he says is the only place in California to have cultured and experimented on H. akashiwo cells, was ready when the organism debuted its first dense bloom in the Bay Area, in 2002. The event was followed by another, smaller bloom in 2004. By this time, researchers, including Cochlan and several of his graduate students, had found out a few things about what makes this particular alga tick. 

Generally, any phytoplankton needs to have the right combination of sunlight, nutrients, salinity and warmth to grow. These conditions are species-specific and limit its growth rate. The Bay, for example, is often a pretty nice place for diatoms. But when the water gets hot and calm, like it has in recent months, conditions become ripe for something else to take over.

In the wings floats H. akashiwo, happy in a wide range of salinities and water temperatures. Since the algae can swim, wiggling their flagella, they can escape from predators like zooplankton grazers, by heading into areas inhospitable to those predators. And by moving up and down in the water column, they can optimise both sunlight and nutrient availability. “They don’t have to worry about the fact that San Francisco Bay is so turbid, because they swim up to the very surface,” Cochlan explains. And crucially, they aren’t picky about food. That food is nitrogen, and it comes in various forms: nitrate, which is highly oxidized, and more reduced forms like ammonium and urea. “This species can grow equally well on all of them,” Cochland says, “even when sunlight is dim, deeper in the water column.”  

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If you’re looking for a villain, it’s hard to blame H. akashiwo for the bloom. It’s just doing what algae do: eating when the eating’s good, and reproducing along the way. To H. akashiwo, the Bay is an all-you-can-eat buffet. Nitrogen comes from waste — human waste, animal waste, fertilizer runoff and refineries are big sources — and not many estuaries receive the astonishing level of nutrient loading that the Bay does. The region has dozens of wastewater treatment plants that release about a half-billion gallons of treated effluent a year and account for more than 60 percent of the dissolved inorganic nitrogen, or DIN, and dissolved inorganic phosphate inputs in the system, according to a 2014 report from the San Francisco Estuary Institute. On average, some 74 metric tons of that kind of nitrogen make their way into the Bay each day. The water’s actually way cleaner now than it was before the 1970s and 1980s, when plants started having to remove contaminants through secondary wastewater treatment. But secondary treatment doesn’t remove much nitrogen, and most plants don’t curb their output of the stuff. So now, as more nutrients pour into the Bay, and climate change heats up the water, we’re likely to see more harmful algal blooms. Including those involving H. akashiwo

Dead yellowfin gobies at Lake Merritt during the algal bloom. (Courtesy of Damon Tighe)

Could we eliminate it? Probably not, says David Senn, senior scientist at the San Francisco Estuary Institute and lead scientist at the San Francisco Bay Nutrient Management Program. “Maybe it’s going to be here forever,” he says. “There’s one way of at least reducing the magnitude of an event like this. And that’s if the nutrient levels were lower in San Francisco Bay.” It’s doable, he added. But it’ll take somewhere “in the vicinity of $10 billion.”

A bloom ends when the algae consume the available buffet, die, and sink. But even here, H. akashiwo triumphs. When stressed, it can form a cyst — a hardy, dormant version of itself — and sink into the sediment, waiting for conditions to become favorable again. This is one possible reason H. akashiwo bloomed again in September after an initial surge earlier in the summer. “The cyst is an environmentally resilient form of the cell. It’s like a seed,” Cochlan says. “So once you’ve had a bloom, you’re likely to have a bloom again. It may be in a few weeks. It may be in a few years. It all depends on which combination of factors triggers the cell to excyst.”

Whenever it will be, researchers may find out about it not only through their ground monitoring, but also because they are looking for HABs from space. The National Centers for Coastal Ocean Science (NCCOS), for example, uses data on surface fluorescence captured by satellites as a proxy for chlorophyll, which in turn is a proxy for phytoplankton biomass. Meanwhile, for the latest bloom, the USGS and SFEI ramped up their monitoring, zigzagging across the South Bay to measure phytoplankton abundance (including H. akashiwo), dissolved oxygen, salinity, suspended sediments, and other parameters. In early September, NCCOS provided the U.S. Geological Survey’s California Water Science Center and SFEI with emergency funding under their HAB Event Response Program, which supports activities like toxin analysis, training, and data collection. 

Collecting all this data will help scientists understand what conditions could lead to toxicity in H. akashiwo blooms here. Back in the Puget Sound shipping container, when Cochlan and his graduate students were experimenting with different H. akashiwo cells, they were constantly tweaking the different nutrient sources, the light levels, the salinities, all to see which combinations would cause H. akashiwo not only to to grow faster and potentially form a bloom, but also make them release toxins. A lot of algae isn’t necessarily a problem. “But if there’s a lot of them there, and they’re producing a lot of toxin, or they increase the toxin per cell — what we call the ‘hotness factor’ — then you’ve got a serious problem,” Cochlan says. “And that’s obviously what we’ve had going on in San Francisco Bay,” he added, because fish were dying even before the oxygen levels plummeted — though detecting toxins, which is a highly specialized task, will take a while to confirm in the lab. The emergency funding that aids such work arrived in tandem with the bloom re-expanding into the Bay. But HAB researchers haven’t always been this fortunate.

All three scientists, Senn, Kudela and Cochlan, agree that in the long term, funding is a major inhibitor to progress on HAB research. “I often say to people, the quickest way to get rid of these harmful algal blooms is to finally get a project funded — the moment you get funded, sure enough, it’s not happening,” Cochlan says. He smiles. But he’s only half-joking. Everyone gets excited about HABs when there are dead fish on the beach, but once the blooms dissipate, we all forget.

But they are coming back. So in the meantime, scientists hope to prepare for the blooms to come by tracking, studying and forecasting HABs better, especially since they aren’t all as benign as H. akashiwo. Researchers from the University of California, Los Angeles, UC Santa Cruz, and the San Francisco Estuary Institute are creating a computer program that combines the high-resolution satellite data and the ground monitoring data to model the algal bloom possibilities for San Francisco Bay and its adjoining coastal area. The most commonly used satellites right now have a 300-meter spatial resolution, but by 2024, this might go down to about 30 meters. Ideally, they’ll pair that with a better understanding of the genetics and physiology of the tiny, weird cells that cause these blooms.

It will require, though, that we spend time, money and effort on the unglamorous work of studying the very, very small — the “flying potato” and its ilk. “You don’t understand how a farm works without understanding what’s growing in the soil,” Cochlan says. “Same thing with the oceans.” 

About the Author

Mukta Patil is a freelance science writer based in the Bay Area. She loves the California poppy, Muir Woods, and Pacifica.