On the tiny Puerto Rican island of Vieques, experience the magic of swimming in bioluminescence.

By Susan C. Kim
June 11, 2009
Frank Borges Llosa

The gleaming waters that once stumped Japanese fishermen and terrified Greek sailors continue to mystify visitor who trek to the sleep village of Vieques, nine miles southeast of Puerto Rico. Travelers speak of Mosquito Bay as if they have seen the Loch Ness monster, with descriptions such as “lit up like fireflies,” “brilliant bursts,” and “beads of light.” My response? I’ll believe it when I see it.

Six months later, I’ve flown between two hurricanes and slept on one airport floor to make good on this statement. Like a child on a field trip, I pile onto a yellow school bus with other spectacle-seekers and hold on for dear life as the rickety vehicle sputters through the seaside hamlet of Esperanza. A few goats dawdling in the road take their time clearing the way for us. A lazy dog doesn’t even bother looking up. Speculation ensues about what we’ll see in this bioluminescent bay (which residents call “biobay” or la bahia).

The tomato-red sun melts into the horizon, revealing the twinkling lights of homes on the hills. But glitter in the bay? So far, nothing. It looks like a typical tropical lagoon―pretty, still, and fringed with mangroves. We push our kayaks out and paddle off with skepticism. Our guide explains that the bay is home to millions of bioluminescent plankton; an average of 450,000 of these prehistoric one-cell organisms (called dinoflagellates) can exist in one gallon of water. Any slight agitation―the wind, a fleeing fish, a hand―causes them to burst into illumination, infusing nearby objects with a spectacular glow.

Bioluminescence is common on the coast, but tour guides claim that la bahia is probably the brightest site in the world because of its delicately balanced environment. The balloon-shape lagoon invites tidal inflow, but a narrow neck restricts the return of dinoflagellates to the ocean. As the guide puts it, “it’s like the Hotel California―you can never check in, but you can never check out.” Red mangroves provides a crucial nutrient, vitamin B12, for the light-emitting organisms. Circumstances conspire to create the perfect habitat for the creatures.

The sky slowly fades from crimson to violet, indigo to ink-black―with no evidence of the moon. It is time. I splash my hand off the side of my kayak and, low and behold, lights bubble to the surface like fluorescent Champagne. Throwing a handful of water in air yields a rain of light. The effect does not produce 100-watt fireworks displays; it’s closer to the eerie blue-green that emanates from glow sticks. A school of fish skitters by in a trail of sparks, and a strong urge compels me to do something I ordinarily would never do―jump into plankton-saturated water and splash around like a baby in a bathtub. Floating in the mysterious liquid and looking up at a starry sky, I feel the awe of being in one of the world’s greatest wonders. That is, for now: This natural phenomenon may be endangered.

In 2003, the U.S. Navy, the island’s largest landowner, turned over control of its holdings to the U.S. Fish and Wildlife Service, inadvertently creating a vacuum for tourism and development. Now, threats to bioluminescence range from increased sedimentation caused by nearby developments, which disturbs the bay’s sensitive balance, to insect repellent, which kills dinoflagellates.

“When I see the faces light up upon their sighting, it reminds me of the first time I experienced the bay,” says Sharon Grasso, who founded Island Adventures, a tour company. “The thrill is still there.” With any luck, the glow will survive to astonish visitors to this serene island for ages to come.

Originally published April 2006