NOAA Fisheries studies Bering Sea bloom

Researchers want to learn how to predict and mitigate bloom effects on marine life

Peacock-hued splashes of color brightened the Bering Sea off the Alaskan coast on October 8, 2009, as the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite flew overhead.

Federal fisheries scientists say they are hoping to witness in September changing colors of the Bering Sea, as they investigate why it happens and what it means for the ecosystem that supports the nation’s biggest fisheries.

Interest in this research dates back to the summer of 1997, when a large area of the deep blue Bering Sea turned milky turquoise, and some 190,000 seabirds died of starvation, scientists with NOAA Fisheries said in a Sept. 20 report from the Alaska Fisheries Science Center.

This colorful transformation repeated for the next few summers, then diminished to less intense blooms. Then in 2014 the phenomenon returned on a large scale, and another massive seabird die-off occurred.

The culprit in the color change, the suspect in the death of the seabirds, is a tiny drifter called a coccolithophore.  These are single-celled marine plants that live in oceans around the world. They play a vital role in regulating atmospheric carbon dioxide, but under certain conditions their numbers can skyrocket locally into enormous “blooms” that cloud the water with potentially catastrophic consequences for other marine life.

Just what those conditions are, why they suddenly set in 20 years ago, and what they portend for the Bering Sea ecosystem is still a mystery.

To find out what’s going on NOAA scientists are tracking late summer coccolithophore bloom extent from 1998 to 2016 using satellite color data.  They are comparing this index with ocean conditions and looking at possible implications for forage fish and predators, NOAA said.


The study was initiated by oceanographers Lisa Eisner of the Alaska Fisheries Science Center and Carol Ladd of the Pacific Marine Environmental Lab, after they found themselves in the middle of a bloom during a Bering Sea research cruise.

Said Eisner, “I wanted to know why is it here and what is its impact?”

Coccolithophores color the water because they are covered in chalk. Unlike other marine algae, coccolithophores armor themselves with plates of calcium carbonate-chalk. They shed multitudes of these tiny white discs, called coccoliths, into the surface water, where they linger long after the coccolithophores are gone. The plates reflect light the same way coral sands do in shallow waters of the Caribbean, with similar shimmering turquoise results.

Those stunning visual effects notwithstanding, coccolithophores can wreak havoc on the ecosystem, NOAA scientists said.

These blooms can cloud the water, making it difficult for visual predators like seabirds and fish to find food, and they may make the food web less efficient, Eisner said.

Because coccolithophores are so small, only very tiny predators can eat them, and every time one creature eats another, it gets only 10 percent of the nutritional value of its prey. When the food web starts very small with more creatures eating others on the way to the top, less nutritional value is left by the time it gets all the way up the long food chain to top predators, like fish, seabirds and mammals, including humans.

To find out why coccolithophores are blooming in the Bering Sea now, where they start and what conditions trigger blooms, Eisner and Ladd’s teams are comparing bloom extent with water temperature, nutrient levels and water column stratification.

There are, however, limitations to the data they are working with, and their future plans involve collaboration with experts on coccolithophores at the University of California at Santa Barbara. “Once we understand what causes the blooms, we will be able to predict and mitigate their effects on Bering Sea marine resources, Eisner said.