I dont know if its something you have to WORRY about, but I would be on the look out and make sure that when you go snorkeling or scuba diving that you have a guide that knows what kind of sea life may be dangerous.
I live in Colorado and certainly dont have any sealife around here, so know very little about it. When my friend and I were in Cancun, we went snorkeling and I saw what I thought was just a rather large mean looking fish. The guide we were with quickly popped his head up and said sternly "barracuda!!!" and rushed us back to the boats. I still dont know how dangerous a barracuda actually is, but I'm glad I am far away from him now
So, moral of story - there is a chance of running into these animals. Just be on the look out and of course never try to mess with them. We are, after all, in their territory.