Too bad its a short stay. I recommend that you meet up with Ras Creek at the Sandbox.. usually around noon. He has a great nature boat trip and you will swim with the nurse sharks and stingrays. Then you get a trip around the island. Creek has been on the island for many years and truly cares about the environment and is very knowledgable.
Sandbox the best for overall good food... Check out Wish Willy for a real dinner treat. I heard that Chocolate's Manatee trip is a great one but I did not have enough time to do everything. Have fun! And remember: GO SLOW!