All that Glitters: Puget Sound in Bloom
For most folks hereabouts, spring translates to some combination of flower gardens and sun. They revel in their tulips and rhodies and poppies. And that’s fair enough. But for f us saltwater souls, it’s all about the glitter. We look forward to that first warm, moonless night, when Puget Sound is flat and dark so we can launch a kayak, escape the city’s incandescent glow, and enjoy an all-organic light show.
It’s a splendid display. Each paddle stroke ignites thousands of tiny explosions of bioluminescent light, reminding us that Puget Sound, for all its ecological woes, still sizzles with life. Puget Sound may be better known for bigger and more charismatic critters – leaping king salmon and frolicking orcas. But the real star power out there belongs to those ever-lovin’, dazzling dinoflagellates.
Dino-who? OK, they’re microscopic, far too small to be seen by the naked eye. But what they lack in size and grandeur they make up for in numbers – thousands to the cup-full of Puget Sound seawater. And sparkle, because these are the invisible “bugs” which, on warm summer nights, flash an LED-like green across the surface of the sound.
They’re best-known to kayakers, who ride closer the surface, the better to enjoy one of Mother Nature’s most spectacular displays. But other boaters see the sparkle in their bow wave, or when porpoise swim past, leaving a trail of glitter reminiscent of Tinkerbell in Neverland.
It happens every year, when the sound awakens from its winter slumber. As the days become longer and warmer, sunlight triggers what scientists sometimes call the “spring bloom.” Countless trillions of microscopic plankton which have overwintered in semi-hibernation in the depths rise in the water column, and begin to feed, or to photosynthesize, and to reproduce like crazy. By early summer, they dominate the ecosystem, clouding the water, triggering a feeding frenzy that sustains virtually everything that lives out there.
The largest of these organisms are about the size of these periods...... The vast majority are much smaller. The explosion is triggered by diatoms, wondrous, single-celled algae enclosed in an exquisite shell of silicon. Fed by sunlight, the diatoms begin to reproduce, one diatom becoming a million within a month. While an individual diatom is quite invisible, their massive blooms can be seen from the air or, in some cases, from space.
The diatoms, in turn, provide food for zooplankton. There are euphausiids and copepods, which are essentially tiny shrimp, and trillions of chaetognaths, needlelike critters that can actually grow big enough to see with the naked eye. The same bloom includes countless newly-hatched fish and crabs and octopus and other sealife that spend their first weeks and months drifting with the plankton, feeding and being fed upon.
In a rich ecosystem like Puget Sound, the result is a vast soup. Scoop a cup of water from the sound and it looks like, OK, water. But take a drop of that water and slide it under a low-powered microscope, and that droplet is transformed into a throbbing menagerie of copepods and chaetognaths and diatoms and everything in between. Watch long enough, and you’ll find the bigger guys feeding on the little guys.
Given the opportunity, and perhaps a reason, some of those guys will sparkle. Hundreds of organisms, from the fireflies back east to deep-water fish, have the ability to glow in the dark or, in scientific terms, “bioluminesce.” It’s a chemical reaction that takes place either as a continuous glow or an instantaneous flash.
Dr. Claudia Mills, a biologist at the University of Washington marine labs in Friday Harbor, studies some 60 to 70 Northwest species of jellyfish, about half of which are bioluminescent. When she paddles at night, she’ll occasionally glimpse the warm glow of a jelly.
But most of what we see at the surface are those everlovin’ dinoflagellates, she says.
Dinoflagellates are actually a diverse family of single-celled organisms, all microscopic, that drift with the rest of the plankton. Each consists of two transluscent cones, joined at the base, with a whip-like appendage that causes it to spin, like a top, according to Richard Strickland, the University of Washington biologist who literally wrote the book – “The Fertile Fjord” – on Puget Sound plankton.
Dinoflagellates don’t qualify as either plants, nor animals, but as algae. They photosynthesize like plants, converting the sun’s energy to food. But they also use those tiny flagella to propel themselves vertically in the water column. During the winter, they’re less active and less abundant. But as the days lengthen, they multiply and move closer to the surface, soaking up energy by day and, when stimulated, glowing by night.
By midsummer, it’s showtime. In most cases, they only glitter at night, employing a circadian rhythm so they don’t waste energy during daylight. Reversing the cycle in a laboratory might take a week or more.
Scientists understand how the process works, Mills says. But why do they glitter? Some years ago, I toured the Scripps Research Institute in San Diego, and spent a couple of hours with a researcher who was trying to answer that question. “We understand the chemistry pretty well,” she said. “But we’re still trying to figure out the function.”
They’re still working on that, says Mills. The prevailing theory is that the luminescence is defensive, serving as a natural burglar alarm or “startle response.” When threatened by larger predators, the dinos flash green, which may attract even larger predators that hopefully will eat their predators, sparing the dino.
Then again, maybe they’re just showing off, treating the rest of us to a glimpse of Mother Nature’s springtime brilliance.
