Dying phytoplankton have once again sucked all the oxygen out of the water along a stretch of the Oregon Coast this summer, creating a hypoxic dead zone that kills any underwater marine life trapped in it.
It is the fifth year in a row that researchers have spotted a dead zone in Oregon waters. And this year, it’s bigger than ever, enveloping half of Washington state’s coast as well.
“Something about the system that’s very fundamental has changed,” said Jane Lubchenco, an Oregon State University marine ecologist who has studied the phenomenon.
It’s too early to know whether the oxygen-starved ecosystem can be linked to global warming, scientists say, partly because what’s causing the hypoxia is linked to cyclical ocean conditions.
In May and June, strong winds over the ocean pulled cold, oxygen-poor and nutrient-rich water from deeper areas and brought it closer to shore, a process known as “upwelling.” Normally, upwelling is good news for the Dungeness crab, rockfish and other species that thrive on plant life.
“Then the winds quieted down. We had no upwelling winds, a couple of weeks of very calm seas and all those microscopic plants that had been growing like gangbusters started to die and sink,” Lubchenco said. “And the bacteria that began to decay used up all the rest of the oxygen in the water.”
Ocean water generally has about 2 to 4 milliliters of dissolved oxygen per liter of water. Anything less than 1.4 milliliters per liter can kill a wide range of marine life. Levels in the current hypoxic dead zone have dropped to as low as .55 milliliters per liter.
Such dead zones are a natural phenomenon, and upwelling is stronger in some years than in others. Off the coast of Chile and Peru and southwest of Africa, researchers have documented upwelling-driven dead zones. The intensity and frequency of the events is on the rise in those countries, Lubchenco said.
The lack of correlation with any El Niño or La Niña events combined with the dramatic swings of recent years could suggest a human link, OSU oceanographer Jack Barth said.
“What I do know is the climate change models for this part of the world say if you heat up the land more, you get a change in upwelling winds,” Barth said. “They’ll be delayed in the spring and stronger late in the year. That’s exactly what we saw last year. What I’m comfortable saying is it’s consistent with climate change.”
In Oregon, the most vulnerable area in recent years has been the central third of the coast between about Newport and Florence, where conditions seem to be conducive to the development of low-oxygen waters, OSU researchers said.
If the dead zones continue, the effect on marine life and the people who rely on it could worsen. Some fish, such as salmon and rockfish, will race away from a dead zone when they can feel the oxygen levels dropping. Other bottom dwellers, such as sculpin and bullfish, hide when they sense something’s wrong – and die.
Reports of dead Dungeness crab currently range from Oregon’s central coast to well into Washington.
Florence crabber Al Pazar figures that he lost thousands, if not tens of thousands of dollars last year after pulling up pots full of dead Dungeness crab during the 2005 dead zone event.
“There were little baby octopus, an inch or two inches big, climbing up my crab lines, trying to get away,” Pazar said. “It’s kind of a sad affair.”
This year he’s heard reports from fishermen who’ve hauled in pots with everything inside them dead.
“You can smell it,” Pazar said. The Register-Guard