Another good spot is right past upper matecumbe key (driving south). There are pull offs from the road. I have found a ton of shallow water nems around the rock piles that are 40 or so feet from shore. They are right before and right after Indian key channel.Come snorkel in the Keys next summer. My wife and I go 3 to 5 times a year. Drive down and do a snorkel at Blackfin Resort (they have a cool island 100 yards from their tiny beach). Snorkel the next 2 days. Drive home on day 4 and get any collected animals settled into a holding tank. There are lots of good spots to snorkel and collect that are beach access (no boat required).
If you haven't looked at this thread yet, there's a lot of good info:
https://www.reef2reef.com/threads/snorkeling-collecting-discussion-group.412414/
And you can always ask me questions!