Remember the real threat behind the executive order is the withholding of state funds for any company that attempts to require proof of vaccination. I have no idea what money the cruise lines all receive from FL. If it’s not substantial they could just ignore the EO anyway. If it’s substantial they may just avoid the state and use out of state ports. If the governor allows the cruise ports to be exempt that opens the door for other businesses to sue over unfair practices. I was under the impression that some of the cruise lines had their own sections of the cruise port terminal similar to airlines having a hub at an airport. If that’s the case they likely are deep in bed with the state.
It's not so easy which is why the EO is unenforceable. What if other national ports require that ships can only visit their port if everyone is vaccinated -- So to visit a Caribbean port... or to sail to New York, etc... The cruise ship is required to check vaccination?
This isn't a "Florida" issue, it is an international issue. DeSantis really has now power.
Even if somehow he could stop them from physically checking at the port --- Ok, all passengers must provide their vaccine proof to the Cruise line prior to departure -- it is provided electronically to the cruise line office in the Bahamas (etc).
But again, State jurisdiction over the ports is very murky. Remember, port security is via the TSA.... DeSantis has absolutely no jurisdiction over the TSA. Further, if the Dept of Transportation issues a regulation requiring vaccination for cruise ships at ports, that would override any order by DeSantis.