SAN DIEGO (CN) – A rare red tide washed up on San Diego beaches this week, lighting the shore with a neon blue glow from bioluminescent phytoplankton.
The spectacular display is caused by large aggregations of dinoflagellates (from the Greek: whirling whips) including Ceratium falcatiforme and Lingulodinium polyedra, which emit a neon blue glow at night, spurred by waves or movement in the water.
Causing a red tide during the day, phytoplankton equipped with their own “sunscreen” gather near the shore at midday to catch more light. At night, the organisms bring stunning displays of bioluminescence to the beaches.
The displays are unpredictable, though a number of physical, chemical and biological factors are required for bioluminescence. The red tide was observed from La Jolla to Encinitas this week, offshore San Diego County.
Dozens of beachgoers gathered at La Jolla Shores Wednesday night to catch a glimpse of the glowing phenomenon. The parking lot was as full as on a late-spring weekend and children ran across the beach with glow sticks in hand.
While the dramatic glow of the red tide was not visible, breaking waves did have a glowing hue.
Dr. Michael Latz, a marine biologist at the Scripps Institution of Oceanography, said in an interview that the displays have appeared in San Diego waters for years.
Southern California’s beaches are not the only ones to experience the algae blooms, which are considered harmful, due to toxins produced by the bioluminescent organisms.
In Florida, the phytoplankton produce an air toxin that causes asthma-like symptoms, Latz said. Other regions, including Puget Sound in the Northwest, experience shellfish toxicity, which Native Americans connected to bioluminescence hundreds of years ago.
Shellfish supply has become so toxic at times that commercial fishing has been shut down, Latz said.
The current red tide in San Diego is not harmful or toxic, though.
“We’re lucky here in Southern California that the organisms that are abundant here are not known to be toxic,” Latz said, though some people can be “sensitive” to the algae bloom in San Diego.
Latz said scientists “don’t really know” why red tides occur, and said the events typically occur in the fall but can take place in the spring, as this week.
The current red tide is “quite patchy” and the bioluminescence can be seen only when the algae bloom gets close to shore, Latz said.
“In general, the more organisms there are, the brighter the bioluminescence,” he added.
Red tide last occurred in San Diego in September 2013 and lasted a week; the previous red tide, in October 2011, lasted a month.
Scientists at Scripps are collecting samples from the red tide to learn more about the genetic makeup of the organisms.
“These are unusual and rare events and they should be enjoyed. … Find wonder in what a great display of nature it is,” Latz said.