Hi
I spent 2 weeks at Cayo Santa Maria about 4 or 5 years back, I can't remember the hotel I stayed at but I spent most days snorkeling and diving.....to be honest, it ranks as one of the dullest places I have been for both. The beaches are stunning, out of this world, but as with most locations in Cuba, there is not much to write home about regarding the marine life. It's pretty terrible for snorkeling and diving.
I have some underwater pictures if you are interested, let me know and I will paste a link.
PS808