Dinoflagellates in Puerto Rico's famed Mosquito Bay put on a bioluminescent display that was once considered among the brightest in the world.

It’s not often you hear the word “disappointing” in a conversation about a starlit kayak trip in tropical waters caressed by Caribbean breezes. But that was the word – disappointing – used by the woman seated behind me in the small island-hopper aircraft that carried us from Ceiba, on the eastern coast of Puerto Rico, to the airfield on the island of Vieques.

My family spent a few days on this small island during spring break this year. We’d been looking forward to a night paddle into Mosquito Bay, a small, sheltered cove known as one of the most dramatic examples of bioluminescence in the world.

Bioluminescence, the phenomenon of animals and plants that glow in response to certain stimuli, exists widely throughout nature, but Mosquito Bay has been an international celebrity due to the intensity of its luminosity. “It contained around 6,000 bioluminescent dinoflagellates in each tablespoon of seawater, hundreds of times more than in the open ocean,” said David Gruber, a marine-biology professor at the City University of New York and co-author of Aglow in the Dark, a book that details the many ways in which scientists have adapted this natural phenomenon to medicine, forensic science and other human uses.

Dinoflagellates are remarkably complex single-celled organisms and are common to both salt and fresh water. There are about 2,200 known species and some, including those which normally crowd the mangrove-ringed waters of Mosquito Bay, produce brilliant light shows when disturbed.

A scanning electron micrograph of Pyrodinium bahamense, the dinoflagellate that gives Puerto Rico's Mosquito Bay its famous glow. ©flickr/FWC Fish and Wildlife Research Institute
A scanning electron micrograph of Pyrodinium bahamense, the dinoflagellate that gives Puerto Rico’s Mosquito Bay its famous glow. © flickr/FWC Fish and Wildlife Research Institute

Scientists believe this display of “living light” serves many functions, one being a predator alarm, a neon-bright sign alerting larger predators to the presence of the smaller predators that are bothering the dinos. But for years, the light displays also have invited tourists by the thousands to marvel at the stunning visuals created when paddling a kayak or swimming in the water.

“It’s like bathing in the stars,” explained a friend who visited the bay years ago, when swimming was still allowed. It’s officially illegal to swim in the bay now, though multiple web sites offering “biobay tours” show photos of kayaks and swimmers in the water, each outlined by a radiant corona of panicked dinoflagellates.

But this past winter, the bay mysteriously went dark, and the panic shifted to the Vieques tourism industry, because the biobay is one of the greatest tourist attractions on the island.

On Vieques, the economic benefit of a healthy environment is not an abstract concept. Tourism on Vieques is fueled primary by nature. The U.S. Navy, more specifically the Navy’s former practice of using parts of the island for bombing practice, discouraged the high-rise hotels, casinos, golf courses and condos that can be a plague on many other Caribbean islands.

In the 10 years since Puerto Ricans drove the Navy out, tourism on Vieques has slowly increased, and it is focused on nature. Eco-tour outfitters depend on the environment for snorkeling, diving, and kayaking. There is only one modern-style resort, and it opened recently. The roads are rough – 4-wheel drive is standard on rental cars. There are two functioning gas stations. Feral horses roam freely, often blocking traffic. Poverty is apparent in the narrow streets of Isabel Segunda.

The income from these tourists is needed more than ever today, as Puerto Rico struggles to bounce back from the effects of prolonged recession. The territory is deeply in debt, and its per-capita income is only $15,200, half that of Mississippi’s.

We loved the place immediately, despite the signs on the beaches warning of the possibility of live bombs left behind by the Navy. “Si no se le cayo, no lo recoja,” they cautioned. “If you didn’t drop it, don’t pick it up.”

And despite the warnings from the woman on the plane, we didn’t want to give up on the biobay tour. And so on a night when the moon was almost new, we boarded a van and bumped over a nearly impassable road to Mosquito Bay. We split into pairs and boarded tandem sit-on-top kayaks. Our guide, mounted on a stand-up paddle board, gave us a safety briefing.

The night was dark and the few lights visible on the shoreline didn’t obscure the brilliant display of stars above us. The Milky Way streamed across the sky and the night breezes kept mosquitos away. The water was just barely cool to the touch. When we stopped by a thick stand of mangroves I slumped backward in my seat staring at the remarkable sky, and missed most of the short talk about the relationship between the mangroves and the dinoflagellates.

Soon we noticed the bioluminescence. As our paddles swept through the water the organisms lit up like tiny marine fireflies. When we paddled fast enough, the kayak’s curved bow turned up a sparkling wake.

But the lights were scattered, like fragments of early LED watches left to swirl timelessly in the water. They didn’t provide the spectacular glow that we’d seen in photos. The Vieques biobay did not shimmer for us like a Disney light show. But we were not disappointed. We’d paid about $40 apiece for a starlit paddle in tropical waters caressed by Caribbean breezes, in the company of a knowledgeable and entertaining guide. The beauty of Vieques will stay with us for a long time, and the visit to the bay was a highlight, not a disappointment.

Since we’ve returned, the bay has continued to perform sluggishly and tours are now open only on weekends, according to The New York Times. No one is yet sure what has caused the bay to dim, although scientists are trying to sort it out, said David Gruber. Theories are abundant, from heavy sea swells that alter the salinity of the bay, to onshore development or other man-made causes that might muddy the waters there.

One of the issues, Gruber says, is that there have been only sporadic research studies of the bay, and this microscopic, single-celled animal has a complex life history and biology. He has been working to collect what is known about the conditions that have allowed Mosquito Bay to provide sustenance for one of the most spectacular populations of dinoflagellates in the world. “This is possibly the first conservation effort to try to restore the conditions for a single microorganism species,” said Gruber.

I hope they figure it out, and find a way to fix it. So many people on the island depend on nature for the income, and I hope to someday bathe in the stars – or at least create a shimmering wake – through Mosquito Bay at its best.


Opinions expressed on TALK and in any corresponding comments are the personal opinions of the original authors and do not necessarily reflect the views of The Nature Conservancy.
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  1. I sure hope they come back. One of the most magical experiences of my life was swimming in that bay. Stars up above, stars down below. Truly phenomenal. Thanks for this post.

  2. Agreed – we visited Vieques on our honeymoon last year, and the biobay was just stunning, even from a kayak, and definitely a highlight of the trip!

  3. Thanks for bringing this up. Is very sad what is going on in P.R. Bioluminescent Bays, between the army years of bombings and neglect,toxic waste left plus P.R. Governments officials lack of knowledge and desire of preservation of this wonders has taken a toll on this and the others bays that we have. Hopefully is not to late.

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