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Phosphorescent Bay; Trillions Of Phosphorescent Dinoflagellates Call It Home

La Bahía Fosforescente; billones de dinoflagelos fosforescentes tomaron posesión de sus aguas

The hazy glow of Phosphorescent Bay got its name from the trillions of phosphorescent dinoflagellates that call it home. Splash into its shallow waters and you'll be given a psychedelic welcome as the micro-organisms burst into an aqua-green flush. El fulgor fuliginoso de la Bahía Fosforescente debe su nombre a los billones de dinoflagelos fosforescentes que tomaron posesión de sus aguas. Chapotee en sus aguas poco profundas y disfrutará de una bienvenida psicodélica mientras los microorganismos prorrumpen hacia un flujo repentino de agua verdosa.

by Frank Prendergast

April 5, 2000
Copyright © 2000 THOMSON CANADA LIMITED or its licensors. All Rights Reserved.

Bahia Mosquito, Puerto Rico -- If there were ever a greatest place for night swimming, Puerto Rico 's Bahia Mosquito would most definitely be a contender.

It's not just the stars piercing through the darkness above, the warm Caribbean breezes, or the symphony of a thousand tree frogs. Bahia Mosquito's most convincing, most spectacular attribute can be found in its shallow waters, which provide an ideal home for millions upon millions of phosphorescent dinoflagellates.

The slightest agitation sends these micro-organisms into a burst of illumination, lighting up nearby objects with an aqua-green glow. Humans included. Lie on your back and make luminescent snow angels. Raise your hand from the water and watch pellets of light drop back into the sea. No wonder the bay is more appropriately known as Phosphorescent Bay.

Its location on the southern shores of Vieques Island (about a one-hour ferry ride east of Puerto Rico 's main island) has meant survival for this truly unique bay and its highly vibrant plankton: The U.S. Navy controls about two-thirds of the island and development has been kept to a dull roar.

And while oil and gas are lethal for dino- flagellates, there is only one shallow nautical access to the bay that, luckily, is not deep enough for most boats to navigate.

Land access, meanwhile, means traversing a dirt road dotted with thigh-deep potholes and jackknife turns, and overgrown with jasmine vines, button mangrove and tamarind trees.

Which means your best bet is an organized tour. I picked the one offered by Island Adventures. We were picked up in a converted school bus at the La Casa del Frances hotel and delivered -- somewhat shaken -- to the shore of the bay, where about 20 of us were herded onto a pontoon boat captained by Mark P. Martin. Over the hum of the electric motor, he explained the "magical" conditions that make Mosquito Bay perhaps the best bioluminescent bay in the world, with a grand total of 720,000 dinoflagellates in a U.S. gallon of water (190,225 in a litre).

The waters of the 64-hectare bay, Martin pointed out, are fed by decaying mangrove trees, providing a soup of essential vitamins and nutrients to the dinoflagellates. The prevailing currents, meanwhile, trap plankton while keeping many predators out. The depths of the bay -- five metres at its deepest -- allow the dinoflagellates to keep near the surface, but safely outside the range of their shallow-swimming enemies: the comb jellyfish, and bay and reef shrimp.

As we neared the middle of the bay, the ripples of water began to take on edges of light, and other designs started to appear beneath the surface. Sardines and other baitfish made the jerky movements, eliciting a display that looks not unlike pocket lights flashing on a cloudy screen. A short distance deeper were the snook and tarpon, with more elongated and less frantic flashes of aqua green. The manta ray made a large but dimmer circle.

The blasts of light (individually measured in fractions of seconds) are believed to be a defense mechanism used by the plankton to scare off or confuse predators -- giving the plankton enough time to scram. The glow is created from the combination of a protein and enzyme that occurs within the organism.

With the boat finally at a standstill, it was time to suit up and experience all this chemical reaction up close and personal. Volunteers shimmied to the front in hopes of being the first into the phosphorescent soup.

Each jump into the water exploded into a cloud of illumination, the lack of a bright moon accentuating the colours. Twirls and twists became blurs of colour. Psychedelia never felt so good. Soon the cluster of swimmers broke off into smaller groups. Lovers giggled as they tested the limits of their own courage.

The climb back on board created a rain of colour as water and light dripped off our bodies. Awestruck, we rode back to shore as Martin charted the stars. The ones above, that is.

Cost for the trip is $20 (U.S). Ten per cent of that goes to the preservation of the bay, which is protected as a nature reserve by the Puerto Rico government. Island Adventures is at

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