Toxic algae found at high levels in SF Bay mussels

High levels of a toxic freshwater algae known to be harmful to humans have been detected in mussels at several locations in San Francisco Bay, scientists said Monday.

Researchers found 10 to 20 times the regulatory limit of the algae, called microcystin, in mussels collected in Berkeley and Alameda during tests in 2015, said Raphael Kudela, a professor of ocean sciences at UC Santa Cruz.

The toxin, also known as blue-green algae, apparently formed in reservoirs, lakes and stagnant freshwater ponds and then flowed into the bay in rivers and creeks, according to a report written by Kudela and published in the journal Harmful Algae.

The discovery is alarming because there is no regular year-round testing for microcystin, which researchers have found remains toxic for two weeks in the ocean and becomes concentrated in shellfish.

In addition to sea otters, birds, crabs and some seals and sea lions eat mussels from the bay.

The researchers also detected low levels of the toxin in commercial oysters from Tomales Bay, but they did not find any oysters above the guidelines for microcystin in fish.

Kudela’s findings are unrelated to the quarantine that the state Department of Public Health puts in place every May through October on eating locally gathered mussels.

Kudela began investigating the algae phenomenon six years ago after investigators determined that sea otters had been dying of liver damage from ingesting microcystin.

The bacteria have been linked to the death of cattle and even dogs that drank the water or swam through the green slime and then licked their fur.