There is a lot of info in this thread about the snorkeling in the Keys.
http://www.reefcentral.com/forums/showthread.php?t=2511350
Rules for collecting corals in the Keys is pretty easy. You need a Florida saltwater fishing license before you can take
anything.
All stony corals, both sps and lps, as well as
all sea fans are 100% illegal anywhere in the state. Soft corals like ricordia, zoas and palys are limited to 5 polyps per person per day. Gorgonians are limited to 6 or 8 (I don't remember) colonies per person per day.
Protected marine sanctuaries and state parks allow no collecting of live corals.
Get caught by FWC with anything illegal and you face huge fines and/or jail time. I've lost count of how many times FWC has stopped me to check. I've been pulled over by a FWC boat, visited while in the water by FWC on a jet ski and checked at the boat ramp as we came ashore. Don't risk it!
I think if you are up front with TSA and have the coral in a
small container they will let you take it onboard. I have brought live corals home from MACNA meetings before. TSA wants to see it, but they are OK with it as the coral inside is alive so the fluid is unlikely to be used as an explosive chemical! Now I may have just been lucky with the TSA agents I've dealt with. Also, others flying home from MACNA may have set a precedent for the folks who work for TSA, i.e. they had seen others with live corals flying home before I got there.