The Night the Sea Was Lit

by Emma Fiala

Have you ever seen water sparkle like a million mini disco balls and glow with every movement?

Our group visited Mosquito Bay in Vieques for a nighttime kayaking tour in order to witness the bay’s naturally occurring bioluminescence. This phenomenon is an interesting reaction where light is produced by an organism, and common examples include fireflies, glow worms, fungi, squid, bacteria, protists and more.

How does it work?

For Mosquito Bay, the bioluminescence is due to the millions of dinoflagellates with luminescent properties. This type of dinoflagellate is called Pyrodinium bahamense. They are single-celled protists that contain dinoflagellate luciferase, an enzyme that allows for the light emitting reaction to occur. For the fellow science aficionados, I will explain the proposed mechanism below (National Science Foundation, 2011).

  1. Dinoflagellates are moved by external forces (e.g. kicking the water)

  2. Mechanoreceptors detect movement and change the voltage of the membrane

  3. Depolarized membranes cause voltage-sensitive proton channels on vacuoles to open

  4. Protons diffuse out of the vacuole into a special part of the cell with dinoflagellate luciferase

  5. The decreasing pH causes the pH-dependent reaction to occur and light to be generated

If that was a bit too technical, these bioluminescent organisms are sensitive to movement, and when moved, will go through a series of steps that, in the end, produce light.

These little organisms seem a bit delicate, what about Maria’s impact?

Pyrodinium bahamense is found mostly in the Atlantic and thrives in salty, warm environments. The tour guide reported that the bay is significantly more salty than the ocean, which provides a better environment for the dinoflagellates. In times of rain, the bay is illuminated due to the mechanical stress of raindrops disturbing the protists, but as rainwater does not have the same level of salinity, the protists float closer to the bottom of the bay and the bay is less luminescent.

Hurricane Maria was devastating to the ecosystem of Mosquito Bay for many reasons: the high winds pushed the dinoflagellates into the ocean. The rainwater diluted the bay. The hurricane damaged the mangroves that provide essential vitamins to the dinoflagellates (NPR, 2017). It wasn’t until many months later that this beautiful ecosystem started to return. Even 17 months post-Maria, the guides say it has still not fully recovered.

Ok, so what was it like for real?

Our group packed into a white van and journeyed in the dark down a dirt road until we reached a secluded area with mangroves, driftwood, and a small entrance between the trees to the bay. We split into six kayaks with 2-3 people per kayak and entered the water, paddling to the center. The bioluminescence was subtle at first and was not easily distinguishable between moonlight and luminescence. Perhaps it was our adjusting eyes to the dark, or perhaps the relative density of dinoflagellates increased towards the center, but we suddenly noticed the glow once we stopped.

For me, the bay did not illuminate as brightly and intensely as you see in stock photos on Google, but it did have a moderate, transient glow when disturbed by movement that transformed into a subtle, but magical sparkle. Each paddle disturbed the protists and we all enjoyed experimenting with water movement. I personally enjoyed picking the water up and throwing it on the surface. This produced more of an instantaneous sparkle. I also enjoyed putting my feet in the water and slowly kicking, watching blueness spiral around my ankles and sparkles rise to the surface. We were given some free time to explore, so my kayak shared ocean-related “dad” jokes and sped around the bay playing tag. We also relaxed and laid out in the kayaks to stare at the stars. The moon was about half full, but the cloud cover was sufficient to see the bay and a variety of constellations (even if we could only identify two).

On a more humorous note, we had no idea that we would be seeing any fish. While admittedly there were only two fish that I saw, one of them leaped out of the water, like a black dagger, and slapped our professor, Gabe, in the side before falling back into the bay and disappearing in a trail of blue.