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Low oxygen levels off coast raise fears of marine dead zones

July 24, 2021 GMT

PORTLAND, Ore. (AP) — Low oxygen levels measured off the coast of Oregon and Washington are raising concerns of large “dead zones” that could decimate crabs and bottom-dwelling fish within them.

The National Oceanic and Atmospheric Administration said this week that researchers have detected unseasonably low oxygen levels in a large area off the Pacific coast, Oregon Public Broadcasting reported.

Year after year of low oxygen levels beginning in the early 2000s led researchers to determine Oregon now has a “hypoxia season” — just as it has a fire season — and this year’s hypoxia season has arrived far earlier than usual.

The start of the hypoxia season is marked by the upwelling of cold bottom water. Winds initiated that upwelling this year around March. Chan said that’s the earliest Oregon ocean-watchers have seen in 35 years.

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That could have major implications for coastal economies, particularly related to the Dungeness crab.

“When it starts really early, we’re giving (oxygen levels) many more months to get lower and (the dead zone to) get bigger in space,” said Francis Chan, who directs the Cooperative Institute for Marine Resource Studies at Oregon State University.

Dead zones happen as winds pick up, driving cold water from the bottom of the ocean toward the surface, according to NOAA. That contributes to blooms of phytoplankton, which once they die, sink to the ocean floor. Bacteria consume oxygen while decomposing the plankton.

Two of the worst hypoxia seasons off the coast of Oregon occurred in 2006 and 2018 when pots with suffocated crabs unfit for consumption were often found.

“Unfortunately, this is another one that’s looking like it could be a landmark year for these hypoxia zones,” said Tim Novotny, communications manager with the Oregon Dungeness Crab Commission.

Researchers are seeking more data to determine the size and intensity of low-oxygen zones this year.