A red tide just offshore San Diego is bringing a spectacular display of bioluminescence to beaches at night.

Bioluminescence expert Michael Latz, a scientist at Scripps Institution of Oceanography at UC San Diego, said the red tide is due to aggregations of dinoflagellates including Ceratium falcatiforme and Lingulodinium polyedra, the latter of which is well known for its bioluminescent displays, with waves or movement in the water causing the phytoplankton to glow neon blue at night.

Red tides are unpredictable and not all of them produce bioluminescence. There is no red tide monitoring program, but the Southern California Coastal Ocean Observing System at Scripps Oceanography performs weekly sampling for potential harmful algal toxins.

Scientists do not know how long the current red tide will last, as previous events have lasted anywhere from one week to a month or more. Bioluminescent displays are viewed best from a dark beach at least two hours after sunset—but of course, visibility is not guaranteed. On Monday, May 7, bright bioluminescence was observed from La Jolla to Encinitas.

Latz said that local red tides of L. polyedra have been known since the early 1900s due to observations by Scripps scientists. There are several Scripps scientists sampling the current red tide to learn more about the genetic and metabolic characteristics of the organisms.

According to Scripps biological oceanographer Peter Franks, the red tide is most visible during the day between 11 a.m. and 1 p.m. At midday, the organisms swim upward to get more light, creating a thin, dense layer near the surface. This upward swimming interacts with the flows of the internal waves that we often see here. The waves propagate onshore, and their circulation patterns create dense accumulations of the red-tide organisms over the troughs of the waves. As you look out over the ocean, you'll see that the red tide typically appears in stripes parallel to shore—these are the internal wave troughs.

You can view the phytoplankton up-close on the Scripps Plankton Camera website. These in-situ images of microscopic plankton are taken under the Scripps Pier and updated every minute.

(The red tide returned in late May 2019.)

Information about red tides from Michael Latz

What makes the reddish color?

The coloration of the water is due to massive numbers of organisms, including the red tide dinoflagellate Lingulodinium polyedra. Each cell contains a little bit of sunscreen that gives it color. On sunny days the organisms swim toward the surface, where they concentrate resulting in the intensified coloration.

Are the long phytoplankton in the Scripps Plankton Camera images diatoms?

These cells are the dinoflagellate Ceratium falcatiforme, not previously known to bloom along the US west coast. Two cells linked together are daughter cells, meaning one cell has just divided.

What is the geographic range of the red tide?

On May 7, bright bioluminescence was observed from La Jolla to Encinitas. We don't know the full spatial range of the bloom.

Why not?

There is no red tide monitoring program, although there is monitoring for the presence of harmful algal toxins. We know a red tide occurs because we see it.

Is the bloom toxic?

The dinoflagellates comprising this red tide do not produce compounds that not known to be toxic. However, some people are sensitive to the red tide so be careful, especially if you exhibit symptoms while near it.

How long will the red tide last?

We don't know. The last red tide in September 2013 lasted one week. The previous red tide in October 2011 lasted a month. Previous red tides have lasted longer.

Why did it form in the first place?

A combination of physical, chemical, and biological factors are thought to be important in allowing a red tide to form.

Why don't we know more about red tides?

It's difficult to study an unpredictable event. There are several Scripps scientists sampling the current red tide to learn more about the genetic and metabolic characteristics of the organisms,