If seeing the manatees is your primary reason for this trip, you may be disappointed. We did see two or three, but not clearly, for very long, and at some distance. They are very shy animals, and don't stick around very long once the boats show up. However, we did see them, and it was a bit exciting.
The snorkeling on this trip was great, however. We first stopped at a small island where we had lunch and snorkeled around the coral a few yards off the island. We saw a very nice variety of fish and many interesting coral formations.
After leaving the island on our way to Shark Ray Alley, we stopped the boat and the guides cast nets for sardines, which they later used to bait the sharks and rays. Shark Ray Alley was unbelievable. I had read about it, but you have to be there to appreciate it. The rays were everywhere, and some were quite large. You don't wear your fins in the water with them because it stirs up the bottom too much, so bring water shoes if you have them. This might ease the stress from fearing you'll step on one of their tails!
On the way back we stopped at Caye Caulker for a brief look-around. It is a nice, quiet, much less traveled island than Ambergris Caye.