It depends on the south Florida beach you are at. I don't think there is much on or near shore along the Miami beaches, but I really can't say as I haven't spent much time there. But along Key Largo (Pennekamp State Park area) and further south along the Keys... yes. And for my money you can't beat Bahia Honda State Park for great off the beach snorkeling. And the next couple of keys to the south for collecting! Just be aware of the state limits and licence requirements as the FWC does patrol (we have been checked several times both on the water and at the boat ramp). And although I've never been fined, I understand that fine are severe!
The variety of things you can find, and how easily things change in the shallows along the Keys is amazing. We have seen tiny hermits by the hundreds on rocks very near shore at times and none at other times. We find all kinds of stuff off Little Money Key most of the time, but in 2014 there was a algae bloom that almost killed everything... well, made the area look like winter up north. It all looked dead, but it was mostly hiding. The next year we found most of the smaller creatures were back, but bigger ones, like the queen conch, were almost wiped out there. In 2016 it appeared that new queen conch had moved into the area. We always find lots of emerald crabs in the shallows. Snails are there, but a bit harder to find. Either side off the highway as soon as you get onto Spanish Harbor Key is great for off the beach snorkeling. Little Money Key, Money Key and Molasses Key are all great if you have a boat. Little Bahia Honda is 1/4 mile off the beach in the state park (no collecting) and you can rent a kayak there to get to the island. The shallows along the east and southeast side of the island have incredible wildlife. More rock boring urchins than you can count! And they make holes in the rocks that make great homes for all kinds of other creatures.
Go slow and watch very carefully and you'll see all kinds of stuff. We've seen several octopus (or whatever the plural form is) and you need to be very observant in order to find one. They have great camouflage and blend into the background perfectly.
BTW, late spring (warming water and no storms) and early fall (still warm water and storms have quit) are great times to do a snorkel trip in the Keys. If you have the time and money, consider a trip to the Dry Tortugas and Ft. Jefferson (see pics below). We are planing 1 or 2 trips there next year and will camp out overnight. They allow night snorkeling and you are 70 miles from Key West and any lights, so the night sky is just crazy with stars.
Enjoy and good luck. And be sure to come back here and tell us how your trip goes. Or ask more specific questions if you have them.
Thanks for all the info Ron! I actually had a chance to take a trip down to the keys this weekend. I stopped by a few places on the side of the road and was able to find some blue legged crabs, they are doing great in the tank so far. I went down as far as mile marker 70.
I'm thinking of trying to find those zoas at Harry Harris park this weekend. The water was pretty cold haha. I will let you know how it goes.