Bright turquoise waters around Sitka are the likely result of a unique algae bloom- this photo was snapped by SEATOR environmental lab specialist Naomi Bargmann over the weekend.

The seas are changing around Sitka this week. Ocean waters have turned a pale, greenish blue color. Researchers at Sitka Tribe of Alaska think a specific type of algae is the cause. It’s non-toxic, but it’s shedding a material you’ve probably been familiar with since elementary school.

Naomi Bargmann and Angela Hessenius are researchers for Sitka Tribe of Alaska. They test a lot of shellfish for paralytic shellfish poisoning, one of the primary functions of the Southeast Alaska Tribal Ocean Research Center. But this week a new organism has caught their attention. They’re called “coccolithophores.” The word is a mouthful, but the little phytoplankton is even more interesting than it sounds. Here’s Hessenius: 

“They’re microscopic, single-celled marine algae,” Hessenius says. “They’re not plants but they perform photosynthesis like plants do. They’re the base of the food web for that reason.”

They’re unique because they make their miniscule but heavy shells out of calcium carbonate — in other words “chalk.” Hessenius describes them as “little chalk-armored spheres,” in the ocean.

Throughout their lives, they shed their plates. Bargmann says the phenomenon is called “marine snow.”

“A lot of it just stays in the vertical column of the ocean,” she says. “Actually they predict that they account for about fifty percent of the marine cycle of carbon in the ocean.”

Bargmann and Hessenius think these coccolithophores are blooming right now, in Silver Bay and in the ocean surrounding Sitka, creating the waters’ startlingly bright aqua hue. But the organisms are so tiny, the two researchers can’t be 100 percent positive, because their plankton nets aren’t small enough to pick them up. Based on what they observed during a paddleboard sweep last week, and the fact that researchers at STA picked up coccolithophore cells at the same time last year, they think it’s a pretty good bet.

While some algae blooms can be toxic, coccolithophores do not produce toxins. Bargmann says she’s read they do account for about 50 percent of the   carbon cycle in the ocean. And conditions in Sitka have been perfect for them to abound.

“They love the waters to be warm, they love them to be nutrient poor, and stagnant,” says Bargmann. “If you’ve looked outside lately, it’s been pretty nice. In the upper sixties, sunny. Not a lot of rain or mixing or upwelling going on,” she continues. “It’s a perfect storm of conditions for them to thrive.”

The biggest concern: They make it hard for predators, like seabirds and fish, to find food. And they’re so small, they put an energy strain on the food web, making it less efficient.

“Only 10 percent (of energy) is transferred, with each step of nutrients,” Bargmann says. “So by the time it gets to something like a fish or a bird, it’s not a very nutrient rich item for them to eat.”

And Bargmann says big algae blooms are occurring more frequently, not just in Sitka, but in colder regions, which was unusual until just two decades ago. 

“In the Bering Sea, they didn’t see a coccolithothore bloom ever, until 1997. That was in conjunction with the El Niño Warming event. They saw another huge event in 2014, when it started to heat up up there,” she says. “We’re creating these conditions which are very ripe for these species to bloom.”

So while coccolithophores are quite striking, and not toxic, they also serve as a very bright and visible reminder of an unusually warm summer in Southeast.

Photo provided by Angela Hessenius, SEATOR marine ecosystem outreach and research coordinator.

Visit the SEATOR website to read more about coccolithophores in Sitka