The crimson tide is back.
Not Alabama’s football team, but the bioluminescent glow from the marine phenomenon known as the red tide.
“It’s intermittent and impossible to predict,” said Scripps Institution of Oceanography scientist and bioluminescence expert Michael Latz, of the recurring phenomenon.
Red tides are caused by aggregations of dinoflagellates (marine plankton) including Ceratium falcatiforme and Lingulodinium polyedra. The latter is known for its bioluminescent displays, with waves or water movement causing the phytoplankton to glow neon blue at night.
Pictures posted recently on social media showed the eerie neon glow. According to several San Diego photographers who captured the effect, the bioluminescent algae bloom was captured along the shores from Torrey Pines State Beach to Ocean Beach.
The range of red tides also varies greatly. There was a really big one in October 2011 that extended up the entire Southern California coast from the Mexican border to Los Angeles.
“It’s usually every couple years, but sometimes it happens in sequential years,” said Latz of the red tide, noting there was a massive one along the San Diego coast in 1995, with a follow-up the next year. It’s happening again, as there was a red tide in 2018, and now another one this year, both starting near the end of May.
The Scripps scientist said the tide’s plankton go through developmental stages, much like the lifecycle of some insects.
“The organisms that produce this tide have a dormant life state called a cyst, that can sink down into the sediment and emerge later,” Latz said. “Local red tides maybe have an internal clock, and a year later they emerge into swimming cells. On a calm sunny day, they’re (plankton) attracted to the sunlight and they swim right up to the surface. If the water is strong enough to stimulate them, they’ll  produce bioluminescence.”
“It is of great scientific interest why that is occurring,” said Latz of the tidal algae blooms. “For me, the bioluminescence is really the spectacular part.”
Latz added scientists have successfully grown red tide plankton. “We just grow them for our research in labs so we can study them even when they’re not abundant on the coast here,” he said.
Scripps scientists continue to sample red tides when they occur to learn more about the genetic and metabolic characteristics of the organisms.
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 shores. These are the internal wave troughs.
Bioluminescent displays are viewed best from a dark beach at least two hours after sunset, though visibility is not guaranteed. 
What’s also mysterious is the timing and duration of red tides, which have lasted anywhere from one week to a month or more. 
Latz said red tides can, but rarely do, contain a chemical neurotoxin that can be harmful to man and other mammals. “Some people who’ve gone out in the surf with them have had dizziness or asthma-like conditions,” he said. “It’s something we are interested in studying.”
There has also been a pronounced seasonality to red tides.
“Historically, they used to happen in early fall,” said Latz. “Then that shifted in the ’90s so that it also occurs in spring. Spring and fall are the times when it happens the most.”