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Scientists Are Closer to Understanding What Makes Ocean's Toxic Algae Bloom

A new study from Oregon State University and the National Oceanic and Atmospheric Administration provides a rare peak below the waves.

October 21, 2016

Last winter was the first time the Dungeness crab fishery in Oregon closed temporarily because of toxic algae in the ocean.  And even just a week ago, another toxic bloom was happening off the coast.   

Scientists are just beginning to understand what triggers these conditions. A study this month from Oregon State University and the National Oceanic and Atmospheric Administration provides a rare peak below the waves.  

The toxin, demoic acid, is sometimes produced by an algae called Pseudo-nitzschia, or PN.  PN does better than most algae when ocean temperatures are high and there isn’t much nutrients in the water.   

When these nutrient-poor conditions are followed by upwelling of rich, cold water from the ocean bottom, the PN are in the perfect position to party.  Their numbers explode. 

When they’re producing demoic acid, it accumulates in the fish, shellfish and crabs that eat them. And that acid, in turn, can poison humans, mammals and seabirds further up the food chain.   

But the problem with studying this toxic algae in the ocean is that you don’t know to start looking for causes until the blooms are already underway.    

This past year, Oregon State scientist Xiuning Du was in the right place at the right time. The study’s lead author had been taking algae counts and recording ocean conditions near Newport in the months before the toxins appeared.  

“And that helped us to understand better about the causes of the bloom,” Du said.   

They were complex — including a combination of upwelling conditions and high water temperatures brought about by a huge mass of warm water called “The Blob” sitting off the West Coast.  

“You have to think about what region - specific case location - and what the specific ocean conditions [are],” Du says.  “For that case, you can understand better the causes, and also… understand other bloom events.”  

Ocean conditions off the West Coast are predicated by natural cycles and variability, but conditions have become more aberrant.  The high number and intensity of toxic blooms can be linked to atypical ocean conditions over the past few years.

"One of the predictions of the climate change models, is that we will in fact have increased variability," says study co-author Bill Peterson of NOAA Fisheries.  

Consequently, there's an urgency to understanding how these anomalous events effect toxic algae blooms.

The economic losses from the closure of Oregon’s razor clam fishery last season is estimated to be at least $5 million.  The Dungeness season was delayed, but eventually opened to strong catches.   

The hope is that this new data will eventually lead to a way to predict toxic algae blooms, giving clam diggers, crabbers and fishermen time to adjust to the dangerous conditions.   

“You could at least warn people this is coming, and they could make other plans,” Peterson says.  “If that’s where their living comes from… they would have enough moths to find another job.”  

The study is published in the journal PLOS ONE.


A crab struggles for air in Hood Canal, which is experiencing some of the lowest oxygen levels in recorded history.

Seth Book

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