The time is now to see bioluminescence on Tomales Bay

Out in the dark on Tomales Bay, the air brisk and the waning moon still well below the horizon, the splash of a paddle creates a spreading blue glow in the black water, then quickly fades.

Nearby kayaks cut shimmering trails through the gentle waves. Another paddle stroke generates a circle of bluish light that ripples in its wake, then disappears.

Fall is high season for bioluminescence on Tomales Bay, a magical phenomenon produced by tiny, single-celled organisms that emit flashes of light when agitated or disturbed. In high concentrations, with many glimmering at once, they may seem to sparkle in the water or light up the drops that fall from a paddle or swirl in your hand.

These creatures, called dinoflagellates, are present in the world’s oceans year-round and bring night-time visitors to Tomales Bay.

But during North Coast autumns, the northwesterly winds that drive ocean currents offshore of California through spring and summer diminish, smoothing waters on the bay and allowing bioluminescent dinoflagellates to flourish. They gain in abundance near the top of the water column and put on spectacular shows for those willing to venture out by night.

“It’s the best visuals you can have without violating the controlled substance act,” quipped Dallas Smith, program manager for Blue Waters Kayaking, a longstanding Point Reyes-area outfitter. The company is one of three well-established commercial tour operators that schedule trips to optimize bioluminescence viewing potential in Tomales Bay, beginning in May or possibly earlier, depending on conditions.

But in later summer and early fall, calmer ocean conditions and warmer surface waters favor dinoflagellate survival, prompting exponential population growth in the bay, according to John Largier, professor of coastal oceanography at the UC Davis Bodega Marine Laboratory.

So while one can view bioluminescence all summer long, “it just gets better,” said Blue Waters Kayaking owner John Granatir.

Autumn also corresponds with shorter days that bring dark to the region earlier, making it possible to get out on the water at sunset without waiting too late. Most fall tours meet up at 5 p.m.

Many companies take out tour groups through November. Some of the companies also offer private tours and overnight camping trips that permit extended viewing of the bioluminescence.

Dinoflagellates’ bioluminescence is the product of reflexive chemical reactions stimulated by pressure on the microorganism’s cell walls, perhaps by the bow of a boat, a hand dipped in the water or the turbulent water itself. Biologists believe it’s an adaptation that helps them startle potential predators or, perhaps, bring what to a predator is the unwelcome attention of an even larger animal.

In some areas, they may be visible right at the edge of the surfline. If a bloom is so large there’s a red tide, the waves themselves may glitter with blue, white or greenish hues.

In Tomales Bay, the glinting creatures are most often seen in the water column.

The phenomenon is best seen in the dark of a still, moonless night, perhaps one darkened further by clouds or thick fog.

Tours groups commonly depart Miller Boat Launch, next to Nick’s Cove in the town of Marshall, around sunset and head to the west side of Tomales Bay to get as far away as possible from the lights of civilization.

Ryan Bruce, a guide with Petaluma-based Clavey Paddlesports, said White Gulch is an advantageous staging site, directly across the bay from the launch, because Hog Island lies smack dab in between, screening out the glare of the lights from Nick’s Cove. He said the dinoflagellates tend to congregate where algae and bull kelp are present.

“We’ve had people from all over the place come out here,” Bruce said, recalling visitors from the West Coast, New York, New Hampshire, even London.

And when they catch their first glimpse of bioluminescence, “they just go nuts for it,” he said. “It’s awesome. People just start picking up the algae and throwing it at each other, and having a good time... It’s pretty fun to see.”

A trip out on the water any time of day brings visitors into close proximity with the abundant marine life of Tomales Bay - bat rays and leopard sharks, seals and seabirds. But wildlife that interacts with bioluminescent dinoflagellates can create particularly interesting effects: flashes of movement or even a shimmering outline of a sea lion or bat ray.

“There’s a lot of activity at night out on Tomales Bay,” said Granatir, “so on a dark, calm night there’s a lot going on.”?But the dinoflagellates, he said, are “my favorite wildlife, I like to say. I’m a big fan of dinoflagellates.”