The octopuses (the only cephs in the keys) are not endangered there but I am not sure what divers can take out (vs fishermen) and you may need a fishing/spearing license. If you will be using a commercial dive boat, you will not likely be able to take out anything, legal or not (most of the dive areas are protected and I am not sure where fishing falls into the "no touch" policy but the dive boats are very strict about leaving things where you find them). There are five octos common to the Keys area (mercatoris, joubini, hummelincki, briareus and vulgaris). If you see one at all though is will likely be the hummelincki or possibly vulgaris unless you are night diving.
Yeah you can't collect in a whole lot of places down there, but I spoke with the FWC and for small bag limits you just need a plain fishing license, and of course you can't collect in protected areas. But thanks, and i'll be keeping an eye out for them