Hi Marianne, we were there in mid-March and while we were snorkeling there were TONS of what is called Pica-Pica (Spelling?) which is Jellyfish larvae (about the size of a thimble). I was pretty worried when I saw them all floating around, but jumped in anyway. They were actually kind of cool to watch on the water surface while snorkeling. However, when I came up once there were a few on my face and they all stung me. Those were the only stings I felt. But when we got out of the water we all had stings all over us. Except for the one on my face, they don't hurt. They do itch though...kind of like ant bites. I believe the season is over now. Also, according to our guide they are not always around; depends on the tides, winds, etc. He said about his job; when there's no pica-pica my job is fun. When there's pica-pica my job is a job. hahaha! Still better than MY job!!
Don't worry about 'em!!!