LOS ANGELES, California » The millions of sardines that were found floating dead in a Southern California marina this week tested positive for a powerful neurotoxin, researchers said Friday.

High levels of domoic acid were found in the sardines, which may have distressed them off the Los Angeles coastline and caused them to swim into the Redondo Beach marina, University of Southern California biologist David Caron wrote in a summary of his laboratory’s findings.

Caron said that he still believes that critically low oxygen levels in the water caused the sardines to suffocate, but it’s possible the toxin may have been one explanation for why they crowded into the marina.

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

Domoic acid is often found in the stomach of fish that have been feeding on plankton during toxic algae blooms. The toxin has been linked to neurological disorders, illnesses and deaths in seabirds, sea lions, sea otters and whales.

Caron’s lab is working to determine if the poisoning was caused by a toxic algae bloom spotted off Redondo Beach on Wednesday.

The presence of the toxin in the sardines could lead to health complications for pelicans, gulls and other sea life that have been feasting on the dead fish.

"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.

The fish died late Monday and carpeted the water’s surface the next morning, stacking up to 2 feet deep in some places. Crews have already scooped and hauled away more than 85 tons of fish to a composting center where they will turn into fertilizer.