Why S. California's Tides Are Glowing Blue

Red tide (bioluminescent dinoflagellates) lighting a breaking wave at midnight.
In a rare occurrence, a tiny organism called Lingulodinium polyedrum causes the tides to look red during the day and glow blue at night.

Mike / Flickr / CC BY-SA 2.0

During the lockdowns, there aren't as many visitors to the beaches in Southern California. But those who venture out at night have been greeted by a bizarre and beautiful sight: the ocean waters emitting a bright blue glow as the waves crashed and the tide came in.

The cause of this unusual phenomenon is a tiny organism called Lingulodinium polyedrum. This dinoflagellate (a type of algae) blooms every few years in the waters around San Diego, forming what is known as a red tide.

While the algae gives the water a soupy red color during the day, nighttime is when the show begins. Every time the algae is jostled — either by the movement of the tides or the slice of a kayak moving through the water — it emits a bright blue bioluminescent glow. The glow is the result of chemicals made inside the algae's body when it is startled. Biologist Rebecca Helm recently described this response on Twitter as “luminous little panic attacks.”

The breathtaking effect appeared earlier this week, and scientists aren't sure how long it will linger, according to the Scripps Institution of Oceanography.

"We don't know how long the current red tide will last, as previous events have lasted anywhere from one week to a month or more, but scientists are continuing to monitor," the institution posted on Facebook. "For your best shot at viewing the ocean's light show, head to a dark beach at least two hours after sunset. Please use caution and make sure to follow social distancing guidelines!"

Bioluminescence is a fairly common phenomenon among certain dinoflagellate species, says Cynthia Heil, senior research scientist at Bigelow Laboratory for Ocean Sciences in East Boothbay, Maine. "It's the same reaction that occurs in fireflies, which is triggered by turbulent motion."

The blooms used to appear every three to seven years, according to Scripps, but they've become much more frequent over the past decade.

However, it's still hard to predict when they will appear since scientists still don't understand the variables that cause the algae to bloom. "A very intricate stage has to be set for this plankton to bloom," Melissa Carter, a programmer analyst at the institute, said in 2012. The exact conditions are not known, but variables could include water temperature, wind speeds, the presence of other bacteria or viruses in the water, among other conditions.

Carter and her fellow scientists study the bloom whenever it occurs and learn what they can when they can. "Every time there is a bloom, we are collecting our standard measurements and this helps in testing basic hypothesis about what we think is happening and adding to our understanding and predictability of future blooms," she said.

In 2017, a student-led team at Scripps developed a model that takes ecological data and can "identify patterns in the apparent randomness that can be used to predict red tides off Southern California," the institution said in a statement. "This research shows that the challenge is being overcome using innovative techniques that offer us information such as how to predict red tides. That’s important for knowing when to close fisheries and swimming areas, and for the health of residents who live along affected waters," said National Science Foundation’s (NSF) Division of Environmental Biology Deputy Director Alan Tessier.

Bloom or bust

blue water from bioluminescence
While the bioluminescence is stunning to see, people should be cautious about getting in the water due to the bacteria feeding on the algae. Bruce Anderson (University of Stellenbosch

In addition to predicting future red tides, scientists are also asking why certain algae species go through boom periods where they form red tides, while others do not. Carter notes that only about five of the 50 or so species they see on a regular basis in San Diego form these massive blooms. "Why does only a small subset of species have the ability to out-compete all the others and dominate the community for weeks to a month at a time?" she asks.

There are other places you can experience similar phenomena. Heil says she has encountered bioluminescent algae in Moreton Bay, Australia, where it is caused by a dinoflagellate called Noctiluca scintillans. In Maine, a species called Alexandium fundyense causes glowing red tides, although it doesn't occur in the same concentrations as the ones in San Diego and Australia. "It just appears almost like stars twinkling in the sea rather than the water itself glowing," she says. One of the most famous places you can see glowing blooms is Bioluminescent Bay in Puerto Rico, where the glow is reportedly bright enough to read by.

If you do happen to encounter glowing waters, take a bit of caution. Although most are harmless, some of them can be slightly toxic if ingested. The algae in Moreton Bay, for instance, contain high levels of ammonia. The red tides in San Diego have been linked to increased levels of ear and sinus infections, although that could be more from the bacteria in the water that are feeding on the algae than from the algae itself.

But no matter where you encounter bioluminescent waters, take the time to stop and enjoy them. "They can be spectacular," Heil says.