Mosquito Bay – The Incredible Glowing Biobay

Mosquito Bay,Vieques, Puerto RicoWhen the U.S. Navy pulled out in 2003, 80% of Vieques was suddenly transformed into the Caribbean’s largest wildlife refuge. Today, development and tourism could endanger Vieques’ natural wonders, including the magical bioluminescence in Mosquito Bay.

It’s almost like something out of a horror movie—the eerie blue-green glow of the waters around you, responding to every flitting fish and swirling oar. But far from being a ghastly environmental freak, the phosphorescence of Vieques Bay is a 100% natural phenomenon, and one you have to see to believe.

In 2003, the U.S. Navy closed its installation on the island of Vieques, off the coast of Puerto Rico, and since then Vieques has begun to boom as an ecofriendly—and still charmingly scruffy-destination. With some 40 palm-lined white-sand beaches, and reefs of snorkelworthy antler coral off shore, Vieques—7 miles (11km) off the big island’s east coast, only an hour by ferry—has an obvious sand-and-sun appeal. But so have many other Puerto Rican beaches; what makes Vieques special is Mosquito Bay, just west of the main town, Isabel Segunda. It’s nickname is Phosphorescent Bay for the way its waters glow in the dark, thanks to millions of tiny bioluminescent organisms called pyrodiniums (translation from science-speak: “whirling fire”). They’re only about 1 / 500 of an inch in size, but when these tiny swimming creatures are disturbed (by, for example, a hovering tour boat), they dart away and light up like fireflies, leaving eerie blue-white trails of phosphorescence.

These pyrodiniums exist elsewhere, but not in such amazing concentrations: A gallon of water in Mosquito Bay may contain upwards of three-quarters of a million such creatures. The local newspaper Vieques Times perhaps says it best: “By any name the bay can be a magical, psychedelic experience.” You can even swim in these glowing waters, a sensation that’s incredibly eerie and cool.

Don’t make the mistake of coming here on a full moon, however—the glow of the pyrodiniums is only discernible on a cloudy, moonless night. If the moon’s out, you can save your money, because you’ll see almost nothing. (Warning: Some tour boats go out to the bay regardless of the full moon—and you won’t get your money back if you’re disappointed).