Boat Through Puerto Rico’s Record-Breaking Bioluminescent Bays
August 19, 2024
4 min read
It started after the sun disappeared over the horizon and night took over. Excitement was in the air as I wobbled onto the small motorboat in my life jacket to find a post on one of the benches. I got lucky, as I sat right by the edge and could nearly reach out to touch the water. It also meant I got splashed a bit as the captain guided us through the mangrove forest.
In the dark of night, it felt intimidating with the mangrove trees creating a tunnel-like path. The water was still and dark, only disturbed by the boat’s forward motion.
That’s when the darkness started to break, the waves and ripples changing to a bright turquoise color. It was all due to microscopic dinoflagellates—single-celled plankton possessing the ability to glow a blue-green light when the water is agitated by contact. Scientists believe it serves as a defense mechanism against predators, mainly microscopic in nature with some crustaceans and jellyfish in the mix.
Pyrodinium bahamense, the dinoflagellate variety that lives in these waters, makes its own food using sunlight just like plants do. However, unlike plants, these tiny creatures are like a glowing factory—more like fireflies—and their presence is what makes a bioluminescent bay.
These bays thrive when there’s a balance in various connected ecosystems, making the combination of warm salt water, seagrass beds, and mangrove forests the perfect recipe for dinoflagellates to concentrate in high numbers in one spot, according to Mark Martin Bras, the director of community relations and scientific research at the Vieques Conservation and Historical Trust (VCHT) nonprofit organization.
These bays’ ecosystems are a rare phenomenon for this variety of dinoflagellate, as they’re exclusive to tropical locations. The small island of Puerto Rico in the Caribbean is home to not one but three of them: La Parguera in Lajas, Laguna Grande in Fajardo, and Mosquito Bay on Vieques Island, a municipality off the east coast of Puerto Rico. What sets these bioluminescent bays apart from others around the world is the fact that they glow throughout the year, whereas others may glow at unpredictable intervals.
La Parguera, the bay I visited, is located on the southwest part of the island in Lajas, about a two-hour drive from San Juan. It is the only bioluminescent bay on the island where swimming is allowed for those who book a tour with the experience. However, La Parguera has the lowest concentration count of dinoflagellates, making it less bright in comparison to the other two bays in Puerto Rico.
Laguna Grande in Fajardo—about an hour's drive northeast of the capital of San Juan—is one of the most accessible bioluminescent bays on the island. It is inside the Las Cabezas de San Juan Natural Reserve, making it a protected area, so you’ll need to book with a tour operator endorsed by the Puerto Rico Tourism Company or certified by the Departamento de Recursos Naturales y Ambientales (DRNA), or Department of Natural and Environmental Resources in English.
During a kayaking tour, guides take you through a short kayak safety training before you start paddling from the harbor to the reserve. It takes up to 30 minutes to get through the channel and weave through the natural tunnels created by the mangrove trees. Here is where you’ll see the water turn bright blue-green as your paddle makes contact with the water.
Lastly, Mosquito Bay is quite special, as the narrow entrances in the bay, the shallow and warm water temperatures, and the mangrove forest ecosystem create a rich and nutritional habitat for the Pyrodinium bahamense variants to flourish. Even the coral reefs located on the outskirts of the bay help slow down the waves and tides, creating a large concentration of these microorganisms in one place. There’s also almost no light pollution due to red light efforts on the coastline, making the night glow that much brighter.
Historically, the high concentration has been constant, with peak times varying year by year, to the point that Mosquito Bay earned a Guinness World Record in 2006 with more than 700,000 per gallon of water concentration of dinoflagellates. At the time, it made it the brightest bioluminescent bay in the world—a record that was compromised after the devastating effects of Hurricane Maria in 2017.
The ecosystem of Mosquito Bay was left with a destroyed shoreline due to erosion, sand dunes, and deforestation of the mangrove forest. It devastated residents as the bay stopped glowing for around eight months.
However, the bay started to glow soon after. Thanks to conservation and research efforts, like The Mangrove Project by the VCHT, dinoflagellates are once again able to thrive in the ecosystem. Despite these challenges, Martin Bras noted that the population has continued to grow and set a new record in March 2019 with over 3 million dinoflagellates per gallon of water.
Witnessing the bright turquoise glow at La Parguera was truly eye-opening. There I was, a little bit skeptical about how bright these microscopic creatures could glow, only to realize that they are, in fact, glowing due to our direct contact with them.
The experience, as well as the lessons I learned through VCHT research efforts, served as a great reminder of how deeply entwined humans are with nature, and how important conservation is for maintaining the natural wonders of our world.
Getting there
- You’ll arrive in Puerto Rico via the Luis Muñoz Marín International Airport (SJU) located in Carolina. Laguna Grande and La Parguera are both located on the main island, while reaching Mosquito Bay will require a short regional flight from SJU or a ferry from the town of Ceiba to get to the island Vieques; if you’re taking the ferry from Ceiba, the earlier departures are best.
- Average Going price for cheap flights to San Juan: $265 roundtrip
How to do it
- Best time to visit: The dinoflagellates glow brighter when there’s no light pollution, including the moonlight. It’s best to book in advance and during the new moon phases. To avoid overtourism and the rainy season, consider traveling during the dry months from December–April.
- Cost: Depending on the tour operator and bioluminescent bay that you visit, prices typically range from $45–$65 USD per person. Tours take up to three hours.
- Tips and considerations: Book with a certified DRNA or PR Tourism Company–endorsed tour operator. Avoid light pollution from flash photography or flashlights, and keep noise levels low as you kayak through the bays. Swimming in Mosquito Bay and Laguna Grande is illegal, as natural body oils or chemicals on the skin, such as certain ingredients on mosquito repellents, can kill the dinoflagellates. As long as you don’t apply creams and bug repellent to your hands, you should be able to touch the water while kayaking. While La Parguera is the only bay that allows swimming, it’s advisable to visit by boat instead to minimize the negative impact on the bay. Mosquito Bay also offers tours paired with stargazing.
Photos courtesy of Discover Puerto Rico
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Published August 19, 2024
Last updated August 30, 2024
