Imagine following a blue fire with your hand as you drag a kayak paddle through pitch-black water at midnight. not reflected light from a lamp on the beach or a phone. Not a ruse. The water itself glowed as you passed through it; it was electric, cold, and alive. Mosquito Bay on the Puerto Rican island of Vieques is officially the brightest bioluminescent bay in the world. It was named by Guinness World Records in 2006 and attracts tourists from all over the world who can’t quite believe the photos are real. They exist. Dinoflagellates are single-celled organisms that produce the glow, and the science underlying their actions is, if anything, more fascinating than the show itself.
Although dinoflagellates are found throughout the ocean, the concentrations that cause a bay to glow at night require very particular conditions: warm, shallow water that is calm and protected, ideally surrounded by mangroves whose decomposing leaves release nutrients that the organisms eat, and a narrow opening to the sea that prevents the population from dispersing.
Key Facts: Bioluminescent Bays & the Organisms Behind the Glow
| Phenomenon | Bioluminescence — light produced by a living organism via a chemiluminescence reaction involving luciferin and luciferase enzyme |
| Primary organism | Dinoflagellates — single-celled phytoplankton; most common species in bio bays is Pyrodinium bahamense; emit blue-green light when disturbed |
| Evolutionary age | Bioluminescence first emerged ~540 million years ago in octocorals; has evolved independently at least 94 times across species |
| World’s brightest bay | Mosquito Bay, Vieques, Puerto Rico — Guinness World Records certified brightest bioluminescent bay (2006); glows year-round |
| Other key locations | Laguna Grande (Fajardo, Puerto Rico), La Parguera (Lajas, PR), Luminous Lagoon (Jamaica), Laguna Manialtepec (Oaxaca, Mexico), Jervis Bay (NSW, Australia), Matsu Islands (Taiwan), Krabi (Thailand) |
| Best viewing conditions | New moon nights (darkest sky), warm calm water, no wind; avoid sunscreen and insect repellent — chemicals stop the glow |
| Nobel Prize connection | Osamu Shimomura, Martin Chalfie & Roger Tsien won 2008 Nobel Prize in Chemistry for discovering green fluorescent protein derived from bioluminescent jellyfish |
| Toxicity note | Many bioluminescent dinoflagellates are toxic to fish and potentially irritating to human skin; swimming is only permitted in select locations |
| Historical note | Charles Darwin observed it from HMS Beagle; Apollo 13 astronaut Jim Lovell navigated back to his aircraft carrier using a ship’s glowing bioluminescent wake |
| Reference | National Geographic — Where to See Bioluminescent Tides |
All of those things are abundant in Mosquito Bay. Pyrodinium bahamense, which roughly translates to “whirling fire from the Bahamas,” is the dominant species that gives Puerto Rico its well-known glow. Its light is produced by a chemical reaction between an enzyme called luciferase and a compound called luciferin, which is triggered whenever the organism is physically disturbed. a paddle motion. A surge. A fish in motion. When the cell senses mechanical stress, the chemistry ignites, causing a brief burst of chilly blue-green light to be released. When you multiply that by the number of organisms per gallon of water, the result is a bay that resembles a tropical lagoon filled with liquid neon.
Humans have been aware of the phenomenon for a very long time. Aristotle and Pliny the Elder both described wood that glowed in the dark, which is a distinct manifestation of bioluminescence brought on by fungi but sharing the same fundamental chemistry. Charles Darwin described the sky above the horizon glowing from reflected light off the water as he watched from the deck of the Beagle as the ship’s bow pushed two waves of what he called “liquid phosphorus” through a dark sea.
He mistakenly blamed it on an electrical component of the atmosphere. It would take another century for the explanation he was missing to materialize, as it required biochemistry that was just not yet developed. Darwin’s confusion over it has a certain allure. even him. The phenomenon is so unexpected.
Even though the chemistry has since been thoroughly worked out, when you fully comprehend it, it still feels amazing. In marine fish, jellyfish, squid, fungi, fireflies, bacteria, and deep-sea organisms that have never seen sunlight, bioluminescence has independently evolved at least ninety-four times throughout the tree of life. A light-emitting molecule and an enzyme to catalyze its oxidation produce a short burst of visible light with nearly no heat, although the underlying reaction varies between species. Scientists refer to it as “cold light.”
Three researchers—Osamu Shimomura, Martin Chalfie, and Roger Tsien—were awarded the 2008 Nobel Prize in Chemistry for their work on Aequorea victoria, a bioluminescent jellyfish whose green fluorescent protein has since developed into one of the most valuable instruments in biomedical research. In a different context, the glow that stops kayakers in their tracks in a Caribbean bay is assisting scientists in tracking cancer cells in living tissue and mapping neural activity.
Photographs don’t convey the fragility of all of this back at the water’s edge. The dinoflagellates that produce the most amazing displays are susceptible to a surprising variety of disturbances, including pollution, salinity, water temperature, and chemical runoff from sunscreen used carelessly by tourists. After decades of high visitor numbers, Puerto Rico’s La Parguera, the only bio bay where swimming is officially allowed, has significantly faded.
In fact, Mosquito Bay brightened considerably following Hurricane Maria in 2017, when the storm’s turbulence paradoxically caused an explosion in dinoflagellate populations—a paradox that scientists are still attempting to fully comprehend. Reduced human activity during the recovery period might have played a role. It appears that the organisms thrive in isolation.
Standing at the edge of one of these bays on a moonless, dark night gives you the impression that you are witnessing something that the planet has been silently doing for half a billion years, long before there were any eyes to appreciate it.
Dinoflagellates use the glow as a defense mechanism. They flash to frighten predators, producing what marine biologists refer to as a “burglar alarm” effect that makes the predator visible to its own adversaries. The organism is not attempting to be attractive. It’s attempting to live. It is completely irrelevant that the outcome may appear to those paddling through it as the most amazing thing they have ever witnessed at night. Even so, it’s worth appreciating.
