The dying of the the day reflects gold and amber and fire-red in the sky over
Wye East River. A September day that has been windy, cloudy and unseasonably
cold finishes with a silent symphony of colors on the westering horizon. Overhead,
the first few stars of evening emerge as a deep violet sky fades ever more quickly
to black. From this vantage point, in a canoe sitting motionless at the mouth
of Pickering Creek, the ebony water and jet-black forest merge into a seamless
tapestry of darkness. For once, it is quiet out on this busy river; no man-made
sound mars the blessed silence. We float without movement, suspended between
sky and water, in perfect quietude, a flawess moment in time and space.
But schedules and obligations call; we break the spell, turn, and paddle for
the solitary light marking the dock at Pickering Creek Environmental Center.
We soon haul the canoes up on the low-tide beach, and look down in wonder where
we step. There, in the wet sand of the receding tide, our footsteps are briefly
outlined in a greenish-yellow glow. Within moments, it fades and is gone. Someone
runs a paddle through the shallows, and it stirs up an even brighter if equally
evanescent light. Water runs off a canoe as it is lifted up the bank; bilgewater
cascades like phosphorescent paint down the steps. We are enchanted by the phenomenon;
although blooms of luminescent algae are well known, few of us have actually
seen them in Chesapeake Bay.
I lay my hand gently atop the water, then remove it and look. Two dozen lights
of cold green fire dot my hand for a moment before fading. Each is a millimeter
or two across, much larger than I would expect from the typical microscopic
algae cells that usually compose luminescent plankton in estuary waters. In
the library the next day, the mystery is solved. The only macroscopic luminescent
alga is not really an alga at all; Noctiluca
is a dinoflagellate, a single-celled protozoa that moves with the aid of a whip-like
flagella. Noctiluca gives off
a flash of light in response to touch or other disturbance. Scientists believe
this spark of green light has evolved as a protection against being eaten; a
predator startled by a suddenly luminescent mouthful of food may release it.
Even the biochemical nature of the flash is known. An enzyme found in Noctiluca,
luciferase, releases light when it converts substrate to product. Other kinds
of organisms have luciferase; the same enzyme causes fireflies to glow on summer
evenings.
Back at the water's edge, I kneel down on the sand and peer into the waters
of Pickering Creek. From a foot away, the water is filled with tiny dots of
light; it is like looking at the stars. But unlike those in the sky, these fluvial
stars blink on and off, tiny pulsars in an infinite galaxy where time is compressed
from millenia into seconds. Every so often, a shooting star streaks across the
firmament; I suspect a grass shrimp, judging by the herky-jerky motion, but
it is far too dark to see.
Those of us who are scientists look at the world, and ask questions: why, how,
wherefore. We study, hypothesize, measure, analyze, compare and examine. But
every now and again, as on this evening, the simple wonder and child-like pleasure
of merely enjoying the natural world takes over. Looking down into the blackness
of water and seeing the stars of heaven winking on and off in a cold green fire
is a mystery both amazing and marvelous.