This will get you to some photos.http://www.reefguide.org/carib/mangroveupsidedownjelly.html
They are always at the Split, but in small numbers, and they try to hug the bottom, so they don't usually hit swimmers. Only if the current is especially turbulent do they get ripped loose and then tumble about helplessly, and may give you a mild spot of rash if they bump into you. Or if people misguidedly kill them, then the dead ones flop about in mid-water and are more likely to sting someone. Jellies are an important food for eagle rays, whale sharks and many other marine organisms!And upside-downs are fairly harmless. Pour vinegar over the sting right away, or use hot water later, and you'll hardly notice the spot the next day.