Ocean waves are glowing blue again on California’s coast. Here’s why

When Melanie Bryan pilots her dinghy through the Morro Bay harbor, she leaves a streak of glowing blue water in the ocean behind her.

“It’s just a splattering of turquoise-glowing blue,” Bryan said. “It’s beautiful.”

The glow is created by bioluminescent dinoflagellates, which are tiny, single-celled creatures that produce bursts of light when disturbed, according to Cal Poly biology professor Alexis Pasulka.

Waves crashing on the sand shake up the plankton — causing them to radiate green and blue light like tiny glow sticks, she explained.

“It’s a beautiful thing to see at night,” Pasulka said.

The catalyst for recent luminous waves are a type of dinoflagellate called lingulodinium polyedra, a reddish brown plankton that also cause red tides, Pasulka said.

As part of the California Harmful Algal Bloom Monitoring and Alert Program, Cal Poly’s Plankton Ecology and Coastal Oceanography Lab monitors for harmful algal blooms off of the SLO County coast.

The lab detected low numbers of these plankton at its Morro Bay test sites, Pasulka said, but there could be pockets of them elsewhere causing small sections of the coast to glow.

“These bloom spots are very patchy,” Pasulka said. “It’s not all encompassing of our coast at the moment.”

Indeed, on Morro Strand near the Rock, no blue waves could be seen at around 9 p.m. on Friday night, but by 1 a.m., the tiny plankton had appeared, illuminating the waves blue to the delight of about 10 people who showed up in search of the phenomenon.

Meanwhile, in Avila Beach, the lab detected 25,000 cells of the plankton per 1 liter of seawater this week — just enough to create a small light show.

Typically, when the entire coastline glows, there are 10,000 to 100,000 cells of plankton per liter of seawater, she said.

Dinoflagellates are often seen off the San Luis Obispo County coast during late summer and early fall when the combination of nutrients and light is just right, according to Pasulka.

The blooms can last several days to several weeks depending on the conditions, she said.

“If, you know, the wind shifts and moves things out of the area, the bloom could be gone within a couple of days,” Pasulka said.

How to see the glowing tides

Bryan has watched the aquatic light show from her sailboat in Morro Bay every night for the past two weeks, she said.

Fish darting through the water stir up the plankton, leaving pockets of neon blue in the harbor, she said.

The bioluminescent plankton are easier to see on dark nights, either during a new moon or when fog blankets the coast, according to Bryan.

High tide is also a better time for viewing as the water is clearer, she said.

“I feel lucky,” Bryan said. “I’ve been living out on the water for 20-plus years, and never do I get sick of it. It’s just surreal.”