Why the Ocean Glows at Night

A gallon of water in Mosquito Bay off Vieques, Puerto Rico holds up to 700,000 microscopic organisms. Disturb them and each one flashes blue-green for about a tenth of a second. Together they light a kayak paddle like a torch, which is why Guinness World Records lists the bay as the brightest on earth.

Glowing water is not rare, and it is not limited to the Caribbean. Florida and Southern California both get it. This guide covers what makes the ocean glow, where to go, and when to show up.

The ocean glows at night because of bioluminescence, light produced by a chemical reaction inside a living organism. An enzyme called luciferase bonds a molecule called luciferin with oxygen, and the reaction gives off light with almost no heat. NOAA estimates more than 75 percent of animals living in the open-ocean water column are bioluminescent, though the glow you see from shore comes from dinoflagellates, single-celled plankton flashing when the water around them moves.

In this article

• Bioluminescence quick facts ↓
• What makes the water glow ↓
• Where you can see it ↓
• Timing, and why animals glow at all ↓
• FAQ ↓

Bioluminescence Quick Facts

What Makes Ocean Water Glow?

Bioluminescence is a chemical reaction with a light bill of almost zero. An enzyme called luciferase bonds a molecule called luciferin with oxygen. The products are oxyluciferin and a photon of visible light. The enzyme survives the reaction and runs it again, which is why a single organism flashes over and over.

Almost none of the energy leaves as heat, so biologists call it cold light. A filament bulb wastes most of its energy warming the room. A dinoflagellate does not.

The light you see breaking over a kayak paddle comes from plankton, not fish. Dinoflagellates flash when the water around them shears or tumbles, which is why the glow follows a wave, a wake, or a hand dragged through the surface. Blue-green travels farthest through seawater, so blue-green is the color most marine organisms produce.

Where You Can See Glowing Water

Mosquito Bay, Vieques

Mosquito Bay holds the Guinness World Records title for the brightest bioluminescent bay, with up to 700,000 dinoflagellates per gallon. The species is Pyrodinium bahamense, and the mangroves ringing the bay feed it while the narrow mouth keeps it penned in. Puerto Rico has three bio bays in all, the other two at Laguna Grande in Fajardo and La Parguera in Lajas. Swimming is restricted at Mosquito Bay to protect the organisms, so kayak tours are the standard way in.

Florida's Indian River Lagoon

The Indian River Lagoon glows from the same organism as Puerto Rico. University of Florida extension describes Pyrodinium bahamense lighting the northern lagoon every summer, flashing when touched as an alarm aimed at predators. Florida runs on a rotation the Caribbean does not: when the water cools, comb jellies take over the show, with the brightest displays reported roughly November through March. This gives the coast two different glowing seasons with two different organisms.

Southern California red tides

Southern California gets its glow from blooms of Lingulaulax polyedra, a dinoflagellate renamed from Lingulodinium polyedra. Each cell is 35 to 60 micrometers across, but billions of them tint the water reddish brown by day and flash neon blue at night when waves break. Scripps Institution of Oceanography notes no monitoring program predicts these blooms, and past events have lasted anywhere from a week to more than a month. Showing up is partly luck.

Timing a Trip, and Why Animals Glow at All

Go dark, go late, go near a new moon

Bioluminescence viewing rewards patience over gear. Scripps advises a dark beach at least two hours after sunset, since eyes need time to adjust and any nearby light washes the glow out. A new moon beats a full moon for the same reason. Motion is the trigger, so a paddle stroke, a breaking wave, or a hand through the water produces more light than still water ever will.

Most of the open ocean is glowing

Glowing water at a beach is the visible edge of something far larger. NOAA estimates more than 75 percent of animals living in the open-ocean water column produce light. Sunlight fades out within the first few hundred meters, so for most of the ocean by volume, the only light available is the light animals make themselves. On this scale, a glowing bay is normal and a dark one is the exception.

Light as alarm, lure, and camouflage

Organisms make light for practical reasons. For a dinoflagellate, the flash works as an alarm: it startles whatever bumped it, and it draws attention to the attacker, which is dangerous for a small predator. Deeper down, other animals use light to lure prey close, to signal a mate, or to erase their own silhouette against faint light from above. Same chemistry, different jobs.

Frequently Asked Questions

What causes the ocean to glow at night?

Glowing ocean water comes from bioluminescence, a chemical reaction in which the enzyme luciferase bonds luciferin with oxygen and releases light. At the surface the source is usually dinoflagellates, single-celled plankton flashing when water moves around them. The reaction produces almost no heat, which is why it is called cold light.

Where are the best places to see bioluminescence in the United States?

Puerto Rico has three bioluminescent bays, and Mosquito Bay on Vieques holds the Guinness World Records title for the brightest. Florida's northern Indian River Lagoon glows each summer from the same species, then switches to comb jellies in the cooler months. Southern California gets bright displays during red tide blooms, though those arrive without warning.

What time of night is best for seeing glowing water?

Scripps Institution of Oceanography recommends a dark beach at least two hours after sunset. Your eyes need the full wait to adjust, and nearby artificial light washes out a faint glow. A new moon helps, and so does anything stirring the water, since motion is what triggers the flash.

Is glowing water the same thing as red tide?

In Southern California the same organism drives both: Lingulaulax polyedra tints water reddish brown by day and flashes blue at night. Not every red tide glows, and not every bloom is harmless, so check local advisories before swimming. Scripps also notes no monitoring program predicts when these blooms will appear.

Why do sea creatures produce light?

Sea creatures produce light for defense, hunting, and communication. For dinoflagellates the flash acts as an alarm, startling a predator and drawing attention to it. Deeper in the ocean, animals use light to lure prey, signal mates, or blend their silhouettes against the dim light filtering down from above.

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About the author: Business Alchemist | Turning Ideas into Products, Brands & Businesses | Navid Malik. Navid is the founder of X2Metal, a metal print studio in North Liberty, Iowa creating bold, durable metal prints and 5mm mouse pads.

Sources: NOAA Ocean Exploration, bioluminescence ↗, Guinness World Records, brightest bioluminescent bay ↗, Scripps Institution of Oceanography, red tides and bioluminescence ↗, Scripps Institution of Oceanography, San Diego red tide ↗, University of Florida IFAS Extension, the glowing lagoon ↗, and Discover Puerto Rico, the island's three bio bays ↗. X2Metal is not affiliated with any organization mentioned in this post.

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