San Juan Islands, Wash. — Right now coastal waters in the Northwest are a bustle. Salmon are running. Killer whales are showing up. And so are algae. Sometimes massive blooms of algae form, making shellfish unsafe to eat. These algae have a little-known cousin that’s bad news for salmon.
Towards the bottom of the marine food chain you’ll find Heterosigma Akashiwo. They’re among the smallest creatures in the ocean. And most of the time, they’re harmless. But every year, in the spring and fall, these microscopic phytoplankton join forces and become the terror of the sea.
“It is a heterosigma soup at times and that is the only cell you’ll see, in the water. You’re talking square miles, you’re talking about millions of cells per liter. The numbers are just amazing,” says Vera Trainer, a lead investigator with the National Oceanic and Atmospheric Administration’s ECOHAB project.
Trainer’s research team is on San Juan Island, trying to figure out what causes spikes in the population of heterosigma – which is lethal to salmon.
In the lab, Trainer points out the magnified image of a salmon’s gill cells. They’ve been exposed to a number of heterosigma treatments, she says.
But why gill cells?
“If you look at a normal fish and a heterosigma-treated fish, the gills are essentially destroyed and they’re basically suffocating,” explains Trainer, who is with NOAA’s Northwest Fisheries Science Center.
It doesn’t take a microscope to observe the ill effects heterosigma have on salmon. Fish exposed to these phytoplankton often leap out of the water, gasping for breath.
These green single-celled organisms are a sort of “super bug” – a monster cross that combines photosynthesis with self-propelled movement. They have two little whip-like tails, or flagella, that propel them through the water column in search of nutrients.
During the winter months Heterosigma lie dormant as cysts on the ocean floor. When warmer weather arrives and the spring rains flush fresh water filled with nutrients into the ocean, they go crazy.
Charles Trick is a professor at Western Ontario University and a member of the ECOHAB team. He says there’s probably a connection between human activity and increased heterosigma blooms in the past 20 years.
“Whether it’s putting fertilizer down, maybe aquaculture, some sort of land use that seems to be causing these species to be more prevalent in our waters now,” he says.
Research suggests that human inputs combined with warming ocean waters may be making conditions extra comfortable for harmful algal blooms.
Trick points out a weird thing about heterosigma: although they’re almost always found in water samples this time of year, they’re not always toxic.
“That’s the secret. As longs as they’re growing fast and they’re happy they’re not making much toxin,” he says. “It’s when their growth is slowing down, they’re starting to compete for other nutrients in the water and that makes them toxic at that stage - sort of that last man standing scenario.”
Heterosigma are scavengers and Trick says secreting a toxin into the water is a way for them to kill the competition for food.
But it’s the big fish - often salmon - that are accidental victims of heterosigma’s destructive quest for nutrients.
Near neighboring Orcas Island, the researchers collect water samples and then stop by to visit Mike O’Connell and Guinness, his big chocolate Lab. O’Connell manages the Glenwood Springs Salmon Hatchery. A short walk from the dock leads to a large pool teeming with juvenile chinook salmon.
“They’ll be coming through here as they are right now, and down the fish ladder and out to sea,” he says.
For several years returning salmon numbers were down and O’Connell didn’t know why. Then he heard about Vera Trainer’s work with harmful algal blooms and started releasing the young salmon earlier in May, before the heterosigma population spiked.
“And we did see a huge number of fish return to our hatchery last year. Over 700, over our average,” he says, “so we were very happy to see that take place and hopefully that will continue in the future.”
O’Connell may have found a way to help his hatchery-raised salmon avoid the hazards of heterosigma, but it remains bad news for wild and farmed salmon alike. Wild salmon migrate on their own schedules, which sometimes means they’re passing through marine waters that are abloom with dangerous algae. And farmed fish spend their lives in stationary net pens, which means there’s no escaping a deadly algal bloom in their neighborhood.
Research on wild sockeye salmon in British Columbia’s Fraser River shows that in years when big heterosigma blooms occur, returning salmon numbers decrease by about 60 percent. Fish farmers lose between 2 and 6 million dollars worth of salmon with each heterosigma bloom.
The ECOHAB researchers want to develop a test that will allow them to figure out immediately whether a bloom is hazardous, and then alert folks who work with salmon. That way hatchery managers like Mike O’Connell will know to release their salmon early, and fish farmers can have some extra notice to harvest their penned salmon before the blooms turn toxic.