NOAA Takes a Closer Look at Bering Sea Bloom

NOAA researchers embarked from Dutch Harbor on September 22, hoping to witness changing colors in the Bering Sea and gather more samples for a continuing investigation in what these changes mean for an ecosystem critical to one of the nation’s biggest fisheries.

Survey samples will be taken from up to a depth range of 70 meters from the southeast Bering Sea to the southwest of St. Lawrence Island, with hopes that in later years more sampling may be done on the shelf area. The focus will be on coccolithophores – single-celled phytoplankton that live in oceans worldwide, and play a vital role in regulating atmospheric carbon dioxide.

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

By clouding the water, they make it difficult for visual predators like seabirds and fish to find food and they make the food web less efficient.

Under certain conditions, the number of coccolithophores can skyrocket locally into enormous “blooms” that cloud water, resulting in potentially catastrophic consequences for other marine life, researchers at the NOAA Fisheries Science Center said.

The researchers are aboard the NOAA ship Oscar Dyson, the first in a class of ultra-quiet fisheries survey vessels built to collect data on fish populations, and conduct marine mammal and seabird surveys and study marine ecosystems.

The summer of 1997 was the first time anyone could remember when a vast swath of the deep blue Bering Sea turned milky turquoise. That year 190,000 seabirds died of starvation. The culprit in the color change, and suspect in the seabird deaths, was coccolithophores. Exactly what conditions cause the blooms to cloud the waters and what they portend for the ecosystem of the Bering Sea is the mystery researchers are trying to solve.

To that end, NOAA researchers have been tracking late summer coccolithophore bloom extent from 1998 to 2016 using satellite color data. They compared this index with ocean conditions and looked at possible implications for forage fish and predators.

The study was initiated by oceanographers Lisa Eisner at the Alaska Fisheries Science Center and Carol Ladd of the Pacific Marine Environmental Lab after they found themselves in the midst of a bloom during a Bering Sea research cruise. The impact of the bloom on commercial fisheries has not yet been determined, they said.