Red Tide Brings Blue Glow To San Diego Beaches

SAN DIEGO COUNTY, CA – A red tide off the San Diego coast is causing local beaches to light up blue at night.

The phenomenon is caused when large numbers of dinoflagellates form a bloom, according to the Scripps Institution of Oceanography at UC San Diego. A bloom filled with bioluminescent phytoplankton has been spotted for the past few nights along the county's coastline, from La Jolla to Encinitas.

Red tides are unpredictable and not all of them produce bioluminescence, according to Scripps Institution of Oceanography. Scientists do not know how long the latest display will last.

The last red tide in the area was in 2013 and lasted a week, according to bioluminescence expert Michael Latz, a scientist at Scripps Institution of Oceanography. A bloom in 2011 was on display for around for a month.

Read more about red tides from Latz:

Scripps Institution of Oceanography: What makes the reddish color?

Latz: 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.

Photo: Erik Jepsen/UC San Diego