Before going for a Caribbean cruise you must make sure that you have all the travel documents that you require to have as a citizen of United States. According to the rules of the region, different traveling situation calls for different requirements. USA issues both passport cards and passport books to their residents. Whether or not the Caribbean cruise will ask for your identity proof in form of passport card, passport book or any other document depends on what type of cruise it is, open loop or closed loop.
Closed loop cruises are cruises that start from and come back in the same port of the United States. According to the regulations set by the Department of Homeland Security of United States, US residents traveling on closed loop cruises may need to present a certified or original copy of their birth certificates and photo identifications issued by the government. They will not need to submit their passports for re-entering USA or staying there.
Open loop cruises are the cruises that start from one US port, but come back to another US port. People traveling on these Caribbean cruises will need to present their valid passport cards or valid passport books. If required, individuals traveling on open loop Caribbean cruises might also show trusted travel documents like NEXUS instead of passport cards or passport books.
For people flying to foreign ports for beginning a cruise or coming back to US on air from a foreign country after completing a cruise must have their passport books with them. Passport cards are not allowed to be used during an international air trip, both to and from the United States.
Whatever may be the related regulations and whichever may be the type of Caribbean cruise you are going for, the best way of avoiding any identification related issues is carrying the passport book with you. This will also save you in time of emergencies or in case you miss a port.