In Cozumel, we decided to take a taxi to Chankanaab park and do the dolphin swim. the taxi cost us $20 for 5 people, but later found out that we should have negotiated the price before getting in the taxi. It only cost $15 on the way back. Oh well....live and learn. We didn't have reservations but I had researched this place online before we left. We paid for the dolphin swim and got in the 10:00 group (11:00 ship time). Somehow we ended up with a group that had paid for the Royal Dolphin swim (maybe because it was the first group of the day) so we got way more than we paid for. We did the dolphin swim (plus some) and got to go in with the Manatee too. We all loved it. Well worth the money.
After doing that, we saw the sea lion show (not much compared to Sea World) and walked over to their beach to do a little snorkeling. The area where you get in the water is very rocky so it was tough for my 7 year old and my MIL, but once you get in the water was beautiful. They had many chairs and umbrellas that you can use. I loved sitting in the chairs in the shade just watching everybody in the water. It's so hot there, that I had no desire to lay in the sun. The shade felt really nice.
We headed back to the ship and did a little shopping on the way. If you're going to shop, this is the place to do it. All the other ports were quite pricey. Cozumel had great prices.