The first time we saw this phenomenon during our stay in Key Largo was in January as we were walking in the evening after dark and I noticed something that looked shiny in the water. I thought it was a reflection of something or a piece of foil in the water. It went out and then returned a few minutes later and I realized that between a few strands of floating sea grass there was a small worm-like creature wiggling and glowing a bright green.
Curiosity aroused, I began asking around about the glowing worm and no one seemed to know what it was. In the Bahamas some years back, we saw glowing jelly fish in the water but this was not a jelly fish. It was definitely a worm or very thin fish.
As time went on, we didn't see any more. Then someone else began asking about the glowing worms in the water. At least I knew now I wasn't the only who had seen them but when we returned to look again at dark we found nothing.
Finally one of our new friends found a link to a study about Bermuda fire worms. The description fit what we had seen. It said that the glowing, or bio luminescence, had to do with the mating that took place every month just after the full moon. When we discovered the date of the next full moon, there was quite a group of us gathered on the dock to see the fire worms.
The peek time is three days after the full moon and 57 minutes after the sun has set. The female rises to the surface and emits a bright green mucus that attracts the male who also emits a glowing mucus. The mucus apparently contains the cells necessary for reproduction. The phenomenon lasts only about thirty minutes and then the worms disappear again.
On the peek night in March, the waters were calm and we could see little worms lighting up all over the place--sort of like the fireflies of summer at home.