When we were at Coco a couple of weeks ago, every night it was calm, a bunch of people would go down to the water to see the dinoflagellates. Apparently they luminesce when you move your hands in the water. Not sure if it's seasonal or not, but you might want to try it next trip, add it to your "nightly routine" I didn't try it myself, I'm not going in the ocean in the dark, but many did and they claim to have seen them...