Puerto Rico has very unique natural resource that has been turned into an eco-tourism attraction – the glowing waters of bioluminescent bays (or bio-bays). Three of these bays exist: La Parguera on the southwest coast; Mosquito Bay on Vieques island; and the most well known and closest to San Juan, La Laguna Grande in Fajardo.
The bays are visited by tourists on sea kayaking tours that often include night kayaking through mangroves.
But what makes the bay glow? These bio-bays contain millions of micro-organisms that glow when agitated – for example in the wake of a kayak. Laguna Grande has a high concentration of these dinoflagellates (the little glowing guys) because as a nature reserve the are has a limited population. Additionally swimming has been outlawed. DEET in insect repellents and the chemicals in sunscreen were killing the dinoflagellates. The nearby mangroves leech B12 vitamins into the waters that help nourish the dinoflagellates.
Spanish explorers during the 17th century thought the water was the Devil’s work, and they tried to kill them by putting rocks at the mangrove entrance. This had the opposite effect, increasing the available food and maintaining the favored warmer water temperatures.