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Toxic algae may have played role in huge fish die-off

March 11, 2011 |  2:50 pm

Fishies Dead sardines in King Harbor have tested positive for domoic acid, a powerful neurotoxin that scientists believe may have poisoned the fish offshore and distressed them as they swam into the Redondo Beach marina, where they suffocated and died en masse earlier this week.

Researchers still believe oxygen deprivation, not the toxin or an algal bloom, caused a million or more sardines to suddenly die Monday night. But the discovery of domoic acid in the dead fish -- reported Friday by USC biologists -- could help explain why they were in the harbor in such huge numbers in the first place.

"It is possible that high levels of domoic acid in the sardines in King Harbor may have exacerbated physiological stress of the fish brought on by oxygen depletion of the water, or may have been a contributing explanation for them congregating in the harbor at very high abundances, but this has not been confirmed," USC Professor David Caron wrote Friday in a summary of his laboratory’s findings to date.

Domoic acid is often found in the stomachs of fish during toxic algae blooms after they consume algae from the ocean surface while feeding on plankton. The toxin has been linked to neurological disorders, illnesses and deaths of seabirds, sea lions, sea otters and whales. When it accumulates in edible fish and shellfish, it can sicken humans.

Caron's lab, which began studying King Harbor after a fish die-off at the marina in 2005, is working to determine if the poisoning was caused by a toxic algae bloom discovered Wednesday about 12 miles southwest of Redondo Beach.

The presence of the toxin in the fish could lead to health complications for seabirds that were seen feasting on the dead fish that carpeted the harbor surface Tuesday morning.

"There were tons of birds feeding on these fish and it’s conceivable that we’ll see some bird mortality as a result," Caron said.

Scientists are also looking into another theory: that a pulse of oxygen-starved ocean water swept into the harbor just before the die-off and worsened conditions for the fish. 

"We know that low oxygen killed them, so the question is: Why was there low oxygen?" Caron said. "Were the waters charged with low oxygen to begin with?"

The California Department of Fish and Game has blamed the massive fish die-off on oxygen deprivation and is also testing fish for toxins at its animal forensics laboratory near Sacramento, where results are not expected until next week.

"It’s going to be a full-on CSI thing with these fish," said spokesman Andrew Hughan. "We’re trying to find out what drove them and why they swam in there. There's the predator theory, there's the rough-water theory; it could be anything, and there may never be a definitive answer."

Crews continue to work to clean up King Harbor using huge vacuums, hoses and nets to remove the fish from the water before they decompose and unleash a powerful stench.


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-- Tony Barboza

Photo: Dead sardines amid a mass fish die-off at King Harbor Marina in Redondo Beach. Credit: Don Bartletti / Los Angeles Times