The plight of an older couple that was put off a Celebrity Cruises ship in Australia mid-cruise illustrates some of the tricky issues facing cruise lines when passengers are afflicted with dementia.

The couple, John and Adry Arnold, had booked a nine-day cruise on the Celebrity Millennium in November to celebrate their 55th wedding anniversary.

Celebrity said it decided to debark Adry Arnold when a housekeeper found her alone and disoriented in her cabin. Her husband was on a shore excursion and could not be reached.

When he returned to the ship, Celebrity had their bags packed and had arranged for an ambulance to take them to a hospital in Cairns. The Arnolds, who live in a town a few hours west of Sydney, will get a pro-rated refund.

In an interview with a TV station in Perth, John Arnold said his wife, 78, has dementia but can still perform familiar activities. “A lot of things she can do by rote, having done it many times,” he told the “Today Tonight” program on Channel 7 in Perth.

Arnold said his wife had been up and down the same staircase on the ship but apparently got confused returning to her cabin. Arnold had been leaving her on the ship at ports for an hour at a time to go ashore.

He told the program he was “gobsmacked” by the decision to remove him, which he said was not explained. “They didn’t tell me a thing,” he said, “except the so-called doctor considered that she was a liability and had to be taken off the ship.”

Arnold was critical of how abruptly he was removed from the ship and said the hospital didn’t know what to do with them when they arrived.

“I’ll always remember the wedding anniversary from being dumped from an American ship in Cairns,” he said.

Royal Caribbean Cruises Ltd., parent of Celebrity Cruises, said in a statement that it acted out of concern for Adry Arnold’s safety.

“Every year, thousands of guests with medical conditions sail onboard Celebrity Cruises ships,” the statement said. “However, for their own safety and the safety of others, these guests must be able to care for themselves.”

Curtis Mase, a Miami attorney who often defends cruise lines in lawsuits, said the liability issues are very real.

“Imagine what happens in this situation where a cruise line allows someone who is physically or mentally not able to take care of themselves to travel without someone, they then cause some kind of safety concern,” he said. “Take your pick: They accidentally lower a lifeboat and injure someone as a result, or they trigger some alarm or go into someplace they shouldn’t have gone.

“All of a sudden the cruise line is liable because they didn’t have a reasonable policy for how someone like that could travel,” Mase said.

He said with advanced notice, the cruise line probably could have arranged an accommodation that would have averted the debarkation.

Cynthia Martinez, a spokeswoman for RCCL, said travel agents with clients who may be mentally diminished should have a conversation about it before booking a cruise.

Mary Beth Lantzy, a spokeswoman for the Alzheimer’s Association, said when considering a trip for someone with dementia, agents should try to visit places that were familiar before the onset of dementia and that involve as few changes in daily routine as possible.