Heavy rains have triggered a bloom of the dinoflagellate Lingulodinium polyedra, an event also known as a "red tide". Nutrients in runoff signal a feeding heyday for the single- celled organisms. If you are lucky you may see their bright blue bioluminescence after dark in the surfline, where the breaking wave action jostles them enough for them to light up in a defense response. According to a UT article by Gary Robbins the glow has been seen in Carlsbad, but not as far as La Jolla. A look at the ocean during the day will show you where the bloom is, a large area of reddish brown discoloration of the water, hence the name. The bloom is definitely visible off of Encinitas, so is worth a look if you are driving on the Coast Highway. Sadly, a closer look is not allowed due to beach closures...
The scanning electron micrograph of the organism above shows the beautiful structure of its "armor". The large groove around the perimeter houses one of the flagellum, or whiplike appendage that helps the animal move. The second flagellum is oriented perpendicular to this one.
The bioluminescence is thought to be a strategy for defense, where if a predator disturbs them they have their own burglar alarm by lighting up. Interestingly, this light is moderated by their own circadian rhythm and can only be triggered at night.
Thank you for the Tankmates post. I enjoyed seeing the whole picture of the layout of your tank, and who is in there. A lot! This looks like a tidepool. Do these creatures need tidal action? Or are they happy just like this? You have inspired me to go find the tidepools we visited in northern California when I was young. Thanks!!