On the blog Deep Sea News, scientist Peter Franks explains in an email exchange to oceanography doctoral student Miriam Goldstein, why the algae appears to glow blue at night.

When jostled, each organism will give off a flash of blue light created by a chemical reaction within the cell. When billions and billions of cells are jostled – say, by a breaking wave – you get a seriously spectacular flash of light.

While red tides may look psychedelic, even non-toxic ones can cause skin and eye irritations, as well as cold and flu symptoms. As the algae bloom, they suck oxygen out of the water and can cause fish kills. Click here to learn the basics of red tide in California.

For a super-scientific explanation of red tides, NOAA has a website, Harmful Algae, dedicated to informing the public on when it is — and isn’t — harmful. It dissects the difference between non-toxic “red tides” and the more toxic variety, which they call “harmful algal blooms,” or HABs.

When HABs happen, seafood, in particular mussels, can accumulate a toxic level of chemicals, which humans should avoid. NOAA’s Harmful Algae site notes:

Filter-feeding organisms like mussels, oysters, clams, and scallops can all accumulate dangerous levels of toxins produced by a few different phytoplankton species. These lethal nerve toxins can also accumulate in the viscera (guts) of crab, lobster, sardines, and anchovies.

Gregg Langlois, senior environmental scientist at the State’s Department of Public Health (DPH) said in an email message that the San Diego bloom “does not pose a threat to beachgoers.” There have been “occasional anecdotal reports of eye irritation and mucous membranes,” which is due to ammonia created by decaying algae, he said. To be safe, the DPH advises people not to come in contact with the bloom, Langlois continued, “even though there is no concern regarding toxicity.”

There is another, less visually-exciting red tide that is lurking along the Sonoma Coast, however. Langolis said officials believe this is associated with “the mysterious death of untold numbers of abalone and other shellfish,” adding that even though red tides in this area are not common, they do occur from time to time.

The state has an annual quarantine of all mussel species harvested along the entire California coast, which continues through the end of October. “The quarantine began early this year,” Langlois said, “because testing by CDPH detected elevated levels of domoic acid which causes paralytic shellfish poisoning.”

Red Tide Glows Blue at Night