I have seen bioluminescent phytoplankton on most Caribbean night dives. Hide your light and move your hand through the water to see “sparks” fly off your fingers. It’s my favorite thing to do during safety stops.
My best encounter with bioluminescence was in June with glow worms in Provo. A few days after each full moon (and about 50 minutes after sunset) glow worms rise up from the sand to mate. I was at the back of our group and taking pictures. After taking some pics of a huge crab, I looked up towards the group, before I grabbed my dive light, and the darkness had turned into a universe of stars. The ocean was full of tiny yellow/green lights - absolutely beautiful!
My wife had a similar encounter in Roatán with what they call string of pearls. They are a small crustacean that use bioluminescent pulses as part of their mating ritual. The phenomenon occurs about an hour after sunset on nights that are pitch black. Turn off your lights and you will see what looks like small strings of light hanging down from the surface.