One of the world’s most enchanting natural wonders, La Reserva Natural de La Bahía Bioluminiscente at Puerto Mosquito is definitely the richest example of a bioluminescent bay. Boats leave glowing trails in the darkness, while swimmers are engulfed by luminous clouds, the water spilling off their hands like glittering fireflies – it’s like something out of a fantasy movie.

The effect is produced by millions of harmless microscopic dinoflagellates, most commonly a protozoa known as pyrodinium bahamense. These release a chemical called luciferin when disturbed, which reacts with oxygen to create light. Experts think that this is a defence mechanism (the glow drawing bigger predators that will eat the creatures feeding on the protozoa) or a way to attract food. Dinoflagellates are found all over the tropics, but Puerto Mosquito has a particularly intense concentration: it’s shallow, has a narrow mouth that acts like a valve, the salinity is perfect (with no freshwater source or human contamination), and the mangroves provide a crucial nutrient boost. Though you can visit the bay on your own, it’s much wiser to use one of the local tour operators, at least at first, to get a thorough introduction to the site.

Surprisingly, most of the land around the bay is private and the main threat for now is artificial lighting, which limits the bioluminescent effect: the Vieques Conservation and Historical Trust is leading the campaign to reduce public and private light sources nearby.

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