Marnie Hunter and Stacey Lastoe, CNN

(CNN) -- The last remaining US cruise ship in Havana Harbor, Royal Caribbean's Empress of the Seas, departed Cuba on Wednesday afternoon.

It was an abrupt end to a burgeoning market for US cruise lines, prompted by a Trump administration announcement Tuesday banning cruise travel to Cuba from the United States.

"This affects nearly 800,000 passenger bookings that are currently scheduled or already underway," according to a statement from industry group Cruise Lines International Association.

"We are disappointed that cruise lines will no longer be operating to Cuba," said Adam Goldstein, the association's chairman. "While out of our control, we are genuinely sorry for all cruise line guests who were looking forward to their previously booked itineraries to Cuba."

Cruise companies have been scrambling since the announcement to understand the implications of the policy change and adjust itineraries accordingly.

Carnival Corporation -- the parent company of Carnival Cruise Line, Holland America and Seabourn -- confirmed Wednesday that the company is no longer allowed to sail to Cuba "effective immediately."

"Currently, Carnival Corporation is sailing to Cuba on Carnival Cruise Line and Holland America Line, and Seabourn has been scheduled to begin sailing in November to Cuba. Additional details for currently booked cruises will be provided by the cruise lines," the company said in a statement.

Carnival Cruise Line offered some details on current and upcoming sailings, including a Carnival Sensation cruise currently in progress.

Guests aboard that ship will call on Cozumel, Mexico, on Thursday instead of Havana. The cruise line extended its apologies and a $100 onboard credit to those passengers.

Carnival Cruise Line is also in the process of notifying guests on upcoming sailings about their options, which include canceling affected itineraries for a full refund, remaining on affected cruises with a $100 per person onboard credit or switching to another itinerary and receiving a $50 per person onboard credit.

Royal Caribbean announced Wednesday that 2019 sailings with Cuban ports of call on Majesty of the Seas and Empress of the Seas will call on alternative ports in the Caribbean. Cruise guests will be permitted to cancel current bookings for a full refund, or maintain their bookings with a new itinerary and receive a 50% refund.

Norwegian Cruise Line said in a statement Tuesday that the company is "closely monitoring these recent developments and any resulting impact to cruise travel to Cuba. We will communicate to our guests and travel partners as additional information becomes available."

Confusion surrounding the ban is palpable among cruise companies, travel websites and passengers with tickets to Cuba.

Erica Silverstein, a senior editor at cruise review site Cruise Critic, said they are fielding questions on what the ban means for people who've paid in full or who are waiting to make final payments on planned trips to Cuba.

"It's worth noting that cruise lines are able to swap itineraries relatively quickly. We see it often during inclement weather, or in the wake of disruption in particular regions," Silverstein said.

The Trump administration policy change also eliminates group people-to-people travel (educational and cultural exchanges of a non-academic nature) as an approved sub-category of travel for Americans.

The Treasury Department in a statement clarified that "certain group people-to-people educational travel that previously was authorized will continue to be authorized where the traveler had already completed at least one travel-related transaction (such as purchasing a flight or reserving accommodation) prior to June 5, 2019."

JetBlue, United Airlines and Southwest Airlines have released statements saying they are reviewing the changes and intend to comply with the new rules.

Under former President Barack Obama, rules around travel to Cuba were loosened, making it easier for individual Americans to comply with certain approved categories of travel without a formal application and approval process.

President Trump tightened those rules in November 2017, only allowing people-to-people travel in groups traveling under the supervision of a US entity.

"That sub-category of travel has been eliminated, but there is a grandfathering provision that basically allows US travelers that have, for example, booked a flight or booked rooms and were contemplating doing a people-to-people trip, they are allowed to complete it," said Pedro Freyre, a partner and chair of the international practice at national law firm Akerman, which has cruise lines and airlines among its clients.

"But that doesn't align with shutting down the ability of the cruises to go in," Freyre said.

It's that misalignment that has cruise lines scrambling to figure out how the new policies will impact their operations.

And it leaves passengers booked on upcoming sailings in limbo.