Some dinoflagellate species produce one or more strong toxins. These toxins are concentrated up the food chain during dense blooms, and can cause illness in humans who consume tainted seafood. The species usually responsible for the red tide off San Diego's coast is not known to be toxic and should pose no health hazard. Locally, the last recorded toxic bloom was in 1902. Red tides are one of many important subjects of study at Scripps Institution of Oceanography.
Flashing is stimulated by mechanical agitation.
After dark, you may observe a bluish glow along the crest of breaking waves. You may also notice your footprints glowing in the wet sand as you walk along the beach. or a fun activity, fill a glass jar with water from the beach. A few hours after sunset, take the jar to a dark room, let your eyes adjust, then give the jar a swirl.